1

KNIGHT GEAR

Group # 6

Sponsor:

None

Group members:

Rene A Gajardo

Do Kim

Jorge L Morales

Siddharth Padhi

I

Ethics Statement and Signature

The work submitted in this Senior Design documentation is exclusively prepared by a team consisting of RENE GAJARDO, SIDDHARTH PADHI, JORGE MORALES, and DO KIM and it is original. Excerpts from other‟s work have been clearly identified, their work acknowledged within the text and listed in the list of reference. All engineering drawings, computer programs, formulations, design work, prototype development and testing reported in this document are also original and prepared by the same team of students.

RENE GAJARDO: __________________

SIDDHARTH PADHI: ___________________

JORGE MORALES: _________________

DO KIM: ______________________

II

Table of Contents 1. Introduction 1

1.1 Executive Summary 1

1.2 Project Description 1

1.3 Motivation and Objectives 2

1.4 Project Requirements and Specifications 3

1.5 Review of similar works 4

2. Literature Survey 5

2.1 Electronic Luggage Follower 5

2.2 Autonomous Robot Luggage 5

2.3 Autonomous Mobile Payload Vehicle (AMP-V) 6

2.4 Autonomous Brilliantly Engineered Cooler (ABEC) 7

3. Design Alternatives 9

3.1 Overview of Conceptual Designs 9

3.1.1 Block Diagram 9

3.1.2 Power System 10

3.1.3 Chassis 10

3.1.4 Wheels and motors 10

3.1.5 Sensors 11

3.1.6 Path Tracking System 11

3.1.7 Obstacle Avoidance System 11

3.1.8 Microcontroller Requirements 12

3.1.9 Motor Controller Requirements 13

4. Project Management 14

4.1 Group Organization 14

5. Engineering Design and Analysis 15

5.1 Chassis and Vehicle Body 15

5.2 Suspension System 16

5.3 Wheel Classification 16

5.3.1 Types of Wheels 16

III

5.3.1.1 Standard or Caster Wheels 17

5.3.1.2 Swedish Wheels 17

5.3.1.3 Spherical or ball Wheels 17

5.3.2 Characteristics of Wheels 18

5.3.2.1 Stability 18

5.3.2.2 Maneuverability 19

5.3.2.3 Controllability 19

5.3.3 Selecting a Wheel Configuration 19

5.3.4 How to Obtain Locomotion 20

5.3.4.1 Differential Driving 20

5.3.4.2 Ackerman Driving 21

5.3.4.3 Synchronous Driving 22

5.3.4.4 Omnidirectional Driving 23

5.3.5 Mechanical Design of Wheeled Robots 24

5.3.6 Braking 26

5.3.6.1 Mechanical Method 26

5.3.6.2 Electronic Method 26

5.3.6.3 Coding Method 27

5.4 Battery 27

5.4.1 Types of Batteries 27

5.4.1.1 NiCad (Nickel Cadmium) 28

5.4.1.2 NiMH (Nickel Metal Hydride) 29

5.4.1.3 Alkaline 30

5.4.1.4 Lithium Ion (Li-Ion) 31

5.4.2 Battery Comparison and selection 33

5.4.3 Recharging the Battery 34

5.4.3.1 Solar Powered Battery Charging 34

5.4.4 Wall Mount Battery Charger 37

IV

5.5 Power Transmission 38

5.5.1 Power Distribution and Regulation 38

5.5.1.1 Texas Instrument Model LM2941 40

5.5.1.2 Linear Technology Model LT3014 40

5.5.1.3 LM7809 Linear Regulator 41

5.5.1.4 LM7805 Linear Voltage Regulator 42

5.5.1.5 PTH0407W Switching Voltage Regulator 42

5.5.1.6 DE-SW050 Switching Voltage Regulator 44

5.5.1.7 Linear Technology Model LT1121 46

5.6 Motors 47

5.6.1 Types of Motors 47

5.6.1.1 Brushed DC Motor 48

5.6.1.2 Brushless DC Motor 49

5.6.1.3 Geared DC Motor 49

5.6.1.4 Stepper Motor 50

5.6.1.5 Servo Motor 51

5.6.2 Motor Controller 51

5.6.2.1 Texas Instruments Model L293D 53

5.6.2.2 Texas Instruments Model SN754410 53

5.6.2.3 Texas Instruments Model DRV 8833 54

5.6.3 Motor Comparison and Selection 55

5.7 Camera or Vision System 60

5.8 Sensors 62

5.8.1 Types of Sensors 62

5.8.1.1 Ultrasonic Proximity Sensor 62

5.8.1.2 Infrared Proximity Sensor 66

5.8.1.3 Sensor Fusion 68

5.8.1.4 Weight Sensor 68

V

5.8.1.5 Accelerometer 70

5.8.1.6 Gyroscope 72

5.8.1.7 Inertial Measurement Units (IMUs) 74

5.9 Wireless Communication 75

5.9.1 Wi-Fi 75

5.9.2 Bluetooth 75

5.9.3 ZigBee 75

5.9.4 XBee 76

5.10 Localization 78

5.10.1 Absolute Localization 79

5.10.2 Relative Localization 80

5.11 Control Algorithm 87

5.12 Microcontroller 92

5.12.1 MC68332 92

5.12.2 PIC 18F452 92

5.12.3 Intel 8051 92

5.12.4 Atmel ATMega2560 93

5.12.5 Microcontroller comparison 93

5.13 Budget and Financing 96

5.13.1 Finance Table 97

5.13.2 Man-hour Costs 98

6. Design Summary of Hardware and Software 99

6.1 Power System 99

6.2 Control System 100

6.3 Motor System 101

6.4 Sensor System 101

6.5 Central Processing System 102

6.6 Code Flow 103

7. Description of Prototype 104

7.1 Prototype Design 104

VI

7.2 Components List 104

7.3 Prototype Construction 105

7.3.1 Frame Assembly 106

7.3.2 Steering System 106

7.3.3 Sensors 107

8. Testing 108

8.1 Safety 108

8.2 Dimensions 108

8.3 Sound Level 108

8.4 System Tests 108

8.4.1 Infrared and Ultrasonic Sensor Tests 108

8.4.2 Simple Movement Tests 109

8.4.3 Simple Following Tests 110

8.4.4 Basic Obstacle Avoidance Tests 111

8.4.5 Advance Maneuvering Tests 112

8.4.6 Indoor Performance Tests 113

8.4.6 Weight Sensors and Solar Recharging Tests 116

8.5 Efficiency 118

9. Engineering Consideration 119

10. Appendices 121

VII

Table of Figures

Figure 1: ELF Conceptual Design 5

Figure 2: Autonomous Robot Luggage 6

Figure 3: Automated Mobile Payload Vehicle 7

Figure 4: Autonomous Brilliantly Engineered Cooler 8

Figure 5: Basic Block Diagram of Knight Gear 9

Figure 6: Omnidirectional Wheels 18

Figure 7: Differential Drive 21

Figure 8: Ackerman Steering Technique 22

Figure 9: Synchronous Driving 23

Figure 10: Omnidirectional Driving 24

Figure 11: Ni-Cad Discharge Rate 29

Figure 12: Discharge Rate of Alkaline Battery 31

Figure 13: Discharge Rate of Li-ion Battery 32

Figure 14: NiMH Battery for Knight Gear 34

Figure 15: Schematic of Solar Panel 35

Figure 16: Tenergy Universal NiMH Battery Charger 37

Figure 17: Typical Application of LM2940 Model 40

Figure 18: Typical Application of LT3014 Model 41

Figure 19: Typical Application of LM7809 Model 41

Figure 20: Typical Application of LM7805 Model 42

Figure 21: Typical Application of PTH0407W Model 43

Figure 22: Power Up Waveform 43

Figure 23: Efficiency of PTH0407W 44

Figure 24: Relative Size and Shape of DE-SW050 45

Figure 25: Efficiency of DE-SW050 Switching Voltage Regulator 45

Figure 26: Typical Application of LT1121 46

Figure 27: Block Diagram of Power Supply of Knight Gear 47

VIII

Figure 28: Geared DC Motor for Knight Gear 50

Figure 29: Texas Instrument L293D Model 53

Figure 30: Texas Instrument DRV8833 Model 55

Figure 31: SN754410 Motor Driver for Knight Gear 57

Figure 32: Schematic of 3 pin SN754410 58

Figure 33: Schematic of 2 pin SN754410 59

Figure 34: LV-MaxSonar EZ Beam Pattern 64

Figure 35: PCB Layout of MaxSonar EZ2 65

Figure 36: Sensing Object within Infrared Proximity‟s Detection Range 65

Figure 37: How Infrared Proximity Sensor Detects Object 66

Figure 38: Building Blocks of Infrared Proximity Sensor 67

Figure 39: Schematics of Load Cell SEN10245 69

Figure 40: Load Cell SEN10245 for Knight Gear 69

Figure 41: ADXL 35 PCB Layout 71

Figure 42: ADXL 335 for Knight Gear 72

Figure 43: PCB Layout of IDG500 73

Figure 44: Xbee Series 2 Chip 77

Figure 45: PNP Inverter 78

Figure 46: EM406 Connector for GPS Module 79

Figure 47: Relative Localization 80

Figure 48: Relative Coordinate System for Localization 84

Figure 49: Determination of Instantaneous Angular and Linear Velocities 86

Figure 50: Controller Block Diagram 87

Figure 51: Effect of Integral Coefficient 88

Figure 52: Effect of Proportional Coefficient 89

Figure 53: Effect of Derivative Coefficient 90

Figure 54: Class Diagram for Control Algorithm 91

Figure 55: Schematic Diagram for Mega Pro 3.3V 94

IX

Figure 56: Pi Connections for Mega Pro 3.3V 95

Figure 57: Power Schematics for ATMega 2560 96

Figure 58: Discharge Curve for 9.6V NiMH Battery 100

Figure 59: Block Diagram of Navigated Control System 100

Figure 60: Code Flow of Knight Gear 103

Figure 61: Flow Chart for the Prototype Software 107

X

Table of Tables

Table 1: Hardware and Software Requirements 3

Table 2: Distribution of Work 14

Table 3: Wheel Configuration 26

Table 4: Approximation of Voltage and Current Consumption 27

Table 5: Battery Comparison 33

Table 6: Motor IC Comparison 56

Table 7: Truth Table of 3 pin SN754410 Motor Controller 58

Table 8: Truth Table of 2 pin SN754410 Motor Controller 59

Table 9: Image Sensor Comparison 61

Table 10: Prepackaged Video Systems 61

Table 11: Ultrasonic Proximity Sensor Comparison 63

Table 12: Infrared Proximity Sensor Comparison 68

Table 13: Accelerometer Sensor Comparison 70

Table 14: Gyroscope Comparison 73

Table 15: IMU Comparison 74

Table 16: Wireless Communication Methods 76

Table 17: Xbee Series Comparison 77

Table 18: Microcontroller Comparison 93

Table 19: Finance Table 97

Table 20: Components List 105

Table 21: Ultrasonic and Infrared Test 109

Table 22: Simple Movement Test 110

Table 23: Following Test 111

Table 24: Obstacle Avoidance Test 112

Table 25: Advanced Maneuvering Test 113

Table 26: Indoor Performance Tests 115

Table 27: Weight and Solar Recharging Test 117

1

1. Introduction

1.1 Executive Summary

Backpacks are a necessity for most college students. Unlike high school, college campuses, like ours here in US, often involves a great deal of walking with little time between classes to run back to dorm rooms or parking lots and exchange the books. Therefore, some students get an idea to carry all the textbooks, laptops, lunches, and basically the rest of their life into their backpacks. This has not only resulted in enormous increase in the weight of the backpacks; in addition, carrying heavy backpacks cause hunchbacks, shoulder pain, back pain, and other upper body pain. This is the reason why our group comes up with the idea to resolve the heavy backpack problem. Our group will develop a self-driving backpack called „Knights Gear‟, which tracks and follows along its owner to the classes and allows the user to walk without lugging it. The objective of our project is making a light weight, low-cost, portable, and easy to use autonomous robot. The main components of Knights Gear are a four wheeled platform with DC gear motors, a microcontroller unit, a motor controller, ultrasonic sensors, infrared sensors, weight sensor, and transmitter. The Knights Gear will be turned on/off manually on the backpack or using the remote controller (transmitter). The weight sensor will be used to determine the weight of payload that Knight Gear works only when the weight of the backpack is less than 50 pounds. If the weight is more than 50 pounds, the robot wouldn‟t move. The rechargeable battery in the Knight Gear will be charged by solar energy. Solar panels will be mounted on the top platform of the robot and will feed the battery during the daylight. The ultrasonic sensors and infrared sensors will be mounted on front side of the robot and they will detect and send the distance between the user and robot, and then microcontroller will calculate the speed and direction to the motor controller. Once motor controller receives the signal, and then it will provide enough power to the each motors and the robot begins to follow the user keeping the distance of 5 feet from it.

1.2 Project description

The Knight Gear is a self-driving backpack that tracks and follows its owner that allows the user to walk without carrying it. The Knights Gear allows certain amount of weight to be conveyed. There is a limit to the weight and the weight sensor takes care of that. If the weight is more than specified then it will not work. Once the weight sensor gives green signal it then, basically, follows the transmitter. The transmitter sends signals to Knight Gear informing its position at all times. Students will have this small and handy transmitter with them. As long as the transmitter is switched on and sending signals to Knight Gear, it will follow

2

keeping enough distance from the user. For the transmitter, ultrasonic sensors are used for the wireless function of the robot. The Knights Gear also uses infrared sensor and ultrasonic sensor to detect and avoid any obstacle in front of it. These sensors prevent the Knight Gear from bumping onto obstacles such as people, wall, and other things on the floor that block its path. Knight Gear also features an automatic shut-down system. If a student stops on the way for more than few minutes then this automatic shut-down feature comes into play. It shuts down the system to save power if the location of transmitter is not changed. The body of the Knight Gear is made to allow aerodynamics. On the platform, which is bottom side of the Knight Gear, all the components are organized in a stable and secure way.

1.3 Motivation and Objectives

They say knowledge is the key to success. If knowledge is the key, then indubitably backpack is a key holder- where books, notes, journals are accumulated. Backpack plays an essential role in students‟ life. Starting from as early as pre-school to graduate schools, students‟ prime source of carrying their notebooks, calculators and educational accessories have been backpacks. However, it is strange that though backpacks have become an important part of students‟ academic life, it has only been recently invented in 1967 by Greg Lowe; and since then many more alterations to it has arrived. Its objective of students easily accessing their books, binders, pen, pencil to school were met, but with conspicuous impediments. As students approach to higher studies, more books and notes supplemented to their backpack. This has not only resulted in tremendous increase in the weight of the backpacks; in addition, carrying heavy backpacks engendered hunchbacks, shoulder pain, back pain, and other upper body pain. Consequently, students started avoiding carrying certain books or notes that might not be necessary for the particular day. Our project will make life easier for students. We propose a thesis that will alleviate these hunchbacks, shoulder pain or any upper body pain due to backpacks. We propose Knight Gear! Knight gear is a tracking robot that will follow its owner or others (if specified) to the classes. The goal of Knight Gear is to completely replace the traditional way of carrying the burden on shoulders; using Knight Gear students can carry heavier weight than they used to by just push of a button. The main goal of our project is to make a light-weight, portable, low cost and easy to use microcontroller inside the backpack that has the ability to detect the owner and calculate the speed and direction to tracks and follows along the user. The Knight Gear should be easy to be used by any person.

3

1.4 Project specifications and requirements In this section, project specifications and requirements will be defined in order to plan the project as shown in Table 1.

Hardware specifications

Size At most 24‟ tall

Raised 6‟ off the ground

Weight 5 lb

Maximum payload 45 lb

Maximum Speed 5 mph

Sensors used Weight sensor

Infrared sensors Ultrasonic sensors

Battery Life Up to 4 hours (rechargeable)

Motors used DC gear motors

Wireless connectivity (transmitter to user)

5-6 feet

Obstacle avoidance Yes

Terrain Indoor/outdoor Paved roads

Software requirements

Programmable in C or C++ is required for the devices

Must be robust to any possible errors

Must be tested before use

The code for the each subsystems must intertwine with each other

Table 1 – hardware specification and software requirements for the project

4

1.5 Review of similar works

The project Knight Gear is similar to other works done in the past, by either previous senior design groups or by other works online. Since the basic function is a robot that follows a specific signal, it is very common to find other projects that have implemented this. In order for the group to learn how others have accomplished this function and how others have built similar style robots, review of other similar works was done.

5

2. Literature Survey

2.1 Electronic Luggage Follower

One of the projects viewed was Electronic Luggage Follower (ELF) from the Florida International University. The purpose of that project was to create a robot that was capable of assisting travelers with their luggage as they go through an airport. The robot was capable of following a single target and avoiding obstacles using sensors. This project, as shown in figure 1, was very similar to our idea for Knight Gear, in that it had the same basic functionality of carrying around a load for a specific user and following said user around. Since obstacle avoidance is also an important function of Knight Gear, this report gave the group some light on the knowhow of achieving this. ELF on the other hand was small and carried a smaller load that what Knight Gear is planned on carrying.

Figure 1 – ELF conceptual design Permission Pending

2.2 Autonomous Robot Luggage

Another project that has inspired Knight Gear is the project Autonomous Robot Luggage, shown in figure 2. This project was done by a hobbyist by the name of Benjamin Heckendorn. His idea was to create a way to have luggage follow a user whenever the user did not want to manually pull the luggage around. The robot luggage he created was a very low cost project because it was meant to be for hobby enthusiast. Benjamin‟s robot showed the group how to implement the basic functions of Knight Gear in a cost effective way.

6

Figure 2 – Autonomous Robot Luggage Permission Pending

2.3 Autonomous Mobile Payload Vehicle (AMP-V)

The AMP-V was a previous senior design project done by group 1 of the University of Central Florida‟s Senior Design class of Fall 2011 to Spring 2012. The idea behind the robot was practically the same as ours, to carry the user‟s payload in a stress-free manner. Doctor Samuel Richie informed us of this project, and told us of parts of which did not work as well as intended. From studying this project we learned to avoid using caterpillar tracks as a means of motions. AMP-V however had a big carrying capacity than the ELF mentioned previously, however its weight to payload ratio was less than desirable with a weight less than 35 pounds and a max payload weight of 25 pounds. The project was solar-rechargeable, and inspired us on our design or our robot. The AMP-V group had to fabricate their own chassis, which can be seen in figure 3, which we used as an inspiration on building our own chassis for Knight Gear.

7

Figure 3 – Automated Mobile Payload Vehicle Permission Pending

2.4 Autonomous Brilliantly Engineered Cooler

(ABEC)

ABEC was a previous University of Central Florida Senior Design project with a

similar objective as Knight Gear, but with a more specific payload. This project

used a premade chassis and used GPS to follow the user. ABEC also utilized 3

ultrasonic sensors in the front of their robot for object detection and avoidance.

From this we took inspiration from their object avoidance system as well as using

their GPS localization and following systems as a backup system to the infrared

and ultrasonic system currently planned for Knight Gear. ABEC can be seen in

the figure below, figure 4.

8

Figure 4 – Autonomous Brilliantly Engineered Cooler Permission Pending

9

3. Design Alternatives

3.1 Overview of Conceptual Design

This section contains all the information about the physical requirements of Knight Gear, extending to the software needed to code the controller algorithms. This also contains information on our design choices for Knight Gear.

3.1.1 BLOCK DIAGRAM

This is the overall block diagram that is supposed to be followed for the implementation of Knight Gear is depicted below in figure 5.

Figure 5 – This is a basic block diagram of Knight Gear.

10

3.1.2 Power System

The Knights Gear needs a good power supply that can put out a reasonable amount of current for the DC motors as well as run a microcontroller and sensors. There are many different types of batteries need to be considered for a power source of the robot. The factors that we will consider for the batteries include: long duration, high performance, fair cost, size and environmental friendliness. Another important consideration for the battery is its recharge ability. It shouldn‟t be take too much time to recharge. Also, in order to operate the Knights Gear for a longer time, the power management systems need to be considered. For instance, if location of transmitter has not changed in 15 minutes and the platform is within the acceptable range of the transmitter, the robot shut-down automatically until the locations of the transmitter is changed. Moreover, using a photocell charger for the batteries shall be a good way to extend the battery life. The solar powered battery charger shall be used to perform this requirement.

3.1.3 Chassis

The designing of the chassis for the Knights Gear is very important, because the main task of the robot is to convey the heavy textbooks. Therefore the chassis should easily bear the heavy weights up to 50 lb. Also, the size of the chassis should be large enough for the batteries, circuits, and the wheels to be installed. The platform of the circuit will be place on the bottom side of the chassis so there must be a protection board above the circuit to protect it from the heavy payloads.

In the design of the platform that would carry backpack, some factors must be taken into consideration. It must be light weight, but of a strong enough material to hold the fully loaded backpack. Also it must be cost effective that designing the entire chassis should not be over 50 dollars.

3.1.4 Wheels and Motor

When deciding on what type of locomotion for Knight Gear we looked at continuous tracks, six-wheel, and four-wheel. Continuous track also known as caterpillar tracks, or tank treads, are a track had of either steel, rubber, or a combination of steel and rubber, rotated by a series of sprockets. The continuous tracks are better than tires through rough terrain and can glide over small obstacles and small gaps in the ground, and are less likely to get stuck in mud. However they lack in speed and maneuverability compared to tires and they are harder to maintain, as the loss of a single segment of track immobilizes the entire vehicle. Additionally, the tracks can slip off their sprockets and jam, which in worst case scenario, the track will need to be broken before the jam can be fixed.

11

Due to the difficulty in maintenance and lower maneuverability and top speed compared to wheels, we decided not to work with continuous tracks and instead focus on a wheel vehicle. From here the decision came down to either using four-wheel locomotion or six-wheel locomotion. In the end our group decided to have four-wheel robotic locomotion for the Knights Gear, because it can handle relatively rough terrain and move at high speeds. While a six-wheel drive could do the similar to a four-wheel drive or marginally better than four wheels, it was more economically reasonable to just go with the four-wheels and four motors. A suspension system shall be required to allow all four wheels to maintain ground contact when the robot encounters the uneven terrain. Also, a deformable tire of soft rubber to the wheel shall be applied to create a primitive suspension. Two main wheels will be powered by dc motors which are independently controlled for steering. The dc motors of the Knights Gear must have enough torque and power to handle the heavy weight of the payload. Also it must be reversible to assist the steering system of the robot.

3.1.5 Sensor The most important task of the Knights Gear is to acquire knowledge about its surroundings. This task will be done by taking measurements using various sensors and extracting meaningful information from those measurements. The sensors must be easy to test and interface well with our selected microcontroller.

3.1.6 Path tracking system

This is the most important part of the project. The ultrasonic sensors will be used to do this job. The ultrasonic sensors are widely used for distance measurement for the autonomous robots. The ultrasonic sensors use sound to measure the time between when a signal is sent versus when its echo is received back. Once the user turn on the device manually or using the remote control (transmitter), the sensors on the backpack receive the signal from it and feed the microcontroller to calculate the distance and direction between them. The Knights Gear will follow its user keeping the distance of five to six feet.

3.1.7 Obstacle avoidance system

The Knights Gear will guide itself when an obstacle comes ahead of it. The ultrasonic sensors and infrared sensors will be used to detect any obstacle ahead of it and send the signals to the microcontroller. This distance information is then used to calculate a destination direction that the Knights Gear must move towards. Then, the motor controller actuating the motors interfaced to it to move the Knights Gear in an alternate direction.

12

3.1.8 Microcontroller requirements

A microcontroller is a computing device capable of executing a program and it is usually responsible for all computations, decision making, and communications. There are many different microcontrollers available on the market ( Arduino, BasicX, Polou, Parallax, BasicATOM etc) and they have different range of products, specifications and potential applications. Therefore, a great amount of research should be conducted to find the right microcontroller for our project.

The microcontroller for the Knight Gear robot shall be small enough to be mounting on the platform. There will be two motors, four-wheels, and a motor-controller on the platform, thus, a small size of the microcontroller will be appropriate. The controller must be low cost but strong enough to take care of many tasks simultaneously. Since the budget of our group is small and limited, it is very important to find a company with a range of products within our budget. Also, the microcontroller must be powerful and capable enough to control and monitor the motor-controller, ultrasonic sensors, and infrared sensors simultaneously. Thus, the microcontroller must carry out enough amount of processing, and which is influenced by factors such as processor clock speed, and internal data bus size and speed. The Word size is another important performance factor to be considered, because it affects the amount of data that the microcontroller can manipulate during a single instruction cycle. It also affects the range of numbers that can be handled. However, a larger word size is not necessarily better for the performance. For instance, if a system functionality can be implemented using a 8-bit Microcontroller, instead of using 16-Bit or 32-Bit Microcontroller. This may increase the complexity of the project and needs extra efforts demanded by the pricy Microcontroller. The controller must also have enough input and output ports. The Knights Gear will have at least two infrared sensors, two ultrasonic sensors, a weight sensor and a motor-controller, thus, the microcontroller must have minimum of six ports on it. Support and documentation is an important factor to be considered as well. Many microcontrollers are open source and have an active online community of supporters. Thus, our group needs to choose the right microcontroller company that has plenty of technical support and active online communities. Programmable language is another factor to be considered. Since most of the group members are familiar with C or C++, the microcontroller relies on these program languages are preferable.

13

3.1.9 Motor controller requirements

A motor controller is an electronic device that acts as an intermediate device between a microcontroller, a power supply and the motors. Although the microcontroller calculates the speed and direction of the robot, it cannot operate them directly because of its limited power output. Therefore the motor controller must be needed for the Knight Gear to provide the enough current for the motors. The motor controller must be small but powerful enough to move the fully loaded Knights Gear. The maximum speed of the robot shall be 5 mph which is faster than the average walking speed.

14

4. Project Management

4.1 Group Organization

In this project of Knight Gear, each person has been given tasks to fulfill. These tasks accumulate to form Knight Gear. If someone in the group doesn‟t complete or gets lazy, then other group members encourage and assist the person to get through the lean patch and to achieve the goal of this project. Everyone offered more than 100 percent in completion of Senior Design I documentation.

Knight Gear is a project that incorporates the various combinations of sub-systems together. These sub-systems were individually divided among the group members to ease the complexity of the design. Each group member did enough research to define, design and implements their respective sub-system and components. The division of the project, Knight Gear, is displayed below in Table 2.

Subsystem Group Member

Main Software Rene Gajardo

Linear Control System Siddharth Padhi

Frame Do Kim

Motors Do Kim

Power Supply Do Kim

Microcontroller Jorge Morales

Sensors Siddharth Padhi

Wheel Configuration Siddharth Padhi

Wireless Communication Rene Gajardo

Video System Siddharth Padhi

PCB Board Jorge Morales

GPS Siddharth Padhi

Autonomous Algorithms Rene Gajardo

Documentation formatting Jorge Morales

Table 2 – Distribution of work

15

5. Engineering Analysis and Design

5.1 Chassis and Vehicle Body

The chassis and body design is very important part of the project. Due to the size and payload of the Knight Gear, it was very hard to find the pre-made chassis from the most of hobby shops. Thus, our group decides to build it using raw materials like wood, plastic, or metals unless we find the pre-made chassis or complete robot kits that chassis and wheels are combined to satisfy the requirement of our robot.

In the design of the chassis, some factors must be taken into consideration. It must be cost effective that designing the entire chassis should not be over 50 dollars. And it must be light weight, but of a strong enough material. Since the main task of Knight Gear is to convey the heavy backpack, the chassis should easily bear the heavy weight up to 50 pounds. Also, the size of the chassis must be large enough for the batteries, electronics, and the wheels to be installed. There are several materials that could be used for the chassis of the Knight Gear.

The wood is extremely light weight and very inexpensive materials that satisfy our light weight, and low cost requirement for the chassis. However, they are very fragile and have low strength that cannot bear the heavy weight of the payload. This drawback of wood makes it unsuitable material for our robot.

Aluminum is another material that could be used for the chassis. They are light weight and very strong material that can withstand the heavy payload. Also, they are not hard to work with. They are very easy to cut, shape, drill and bend so that working with. Moreover, aluminum has very high thermal conductivity; it can be function as the heat sinks for the robot. Only drawback of this material is that their price is quite expensive. Thus it would not be the cost effective to use the aluminum as basis material for the entire body of the robot.

The High Density Polyethylene or HDPE is another material that could be used for the chassis. The HDPE is very widely used in the chassis design of robot because it is inexpensive and very light but strong that have higher strength to weight ratio than metals. Also, the HDPE has very low thermal conductivity that it would be perfect for base part of the Knight Gear where the most of heat is generated.

In conclusion, our group decide to use both HDPE and aluminum materials to design our robot. The HDPE will be used as basis material for the robot that platforms and sides of the robot will be made with this material. The aluminum will be used to connect the HDPE sheets, and to reinforce the strength of the base platform. According to the mcmaster.com, price of the 24‟x48‟x0.25‟ HDPE sheet is 27.30 dollars. This is large enough to make the every structural component.

16

5.2 Suspension system The reason that suspension system is needed for the Knight Gear is because our robot will have four wheels. When the four wheels are used in robot, it is not guaranteed that all the four points are on the plane. If the terrain is not even, such as the robot should climb over some small object, one of the wheels will lift off from the ground. This could potentially cause the robot to fall off to the ground. Moreover, if no suspension system is installed, the robot would receive high frequency shock from the ground. This vibration could damage the electronic devices on the robot, and also loosening the bolts that connects the joints of the robot body. Thus suspension system is highly recommended for the Knight Gear to increase the mobility over rough and uneven terrain and prevent the damage from the load. However, developing the suspension system is not quite easy. They involve many complicated parts, calculations, and are very expensive. The pre-made suspension part is already available in many robot shops but they are too pricy (minimum price is 30 dollars for each side). Therefore our group will develop simple suspension system by ourselves. We will simply install rubber of spring shock absorber for the each motor mount to function as suspension system. Although its performance would be quite low compare to the pre-made suspension system, we believe that it would help the mobility and prevent the vibration of the Knight Gear.

5.3 Wheel Classification

5.3.1 Types of Wheels

Just like any other robot, Knight Gear needs a locomotion mechanism to enable movement through its surroundings. There are several mechanisms to accomplish locomotion but most of them are either legged or wheeled. As far as Knight Gear goes, wheel is more appropriate option to enable movement than legged. Wheels are relatively easy to mechanically implement on Knight Gear. Balance control is not an issue because Knight Gear will have 6 wheels. Wheeled locomotion is also very power efficient, even at high speed. Stability is also not a major concern in wheeled vehicle. It will provide smooth transition while carrying a load 50lbs. Selecting the right type of wheel is almost as important as choosing the type of sensors and motors.

Wheels contradict broadly in terms of their performance in kinematics; as a result selecting the right type of wheels depends on the overall kinematics of Knight Gear. While wheels‟ kinematics decide what type of motion is achievable, wheel‟s geometry is also key factor to look into which will be closely linked to Knight Gear. The composition of wheel‟s kinematic and its arrangement dictates the stability, maneuverability, and controllability of a vehicle. For instance, a car uses Ackermann wheel configuration where there are two wheels in the front are steerable and non-motorized and the two wheels in the rear are non-steerable but are motorized. The wheels are connected to an axis. A lot of automobile

17

companies use this configuration for cars because it provides maximum stability, maneuverability and controllability for a given environment. In case of Knight Gear, it is difficult to select a wheel that will provide optimum results because it has to run indoors and outdoors including grass. There are about 4 different types of basic wheels. These are the following listed below:

Standard wheel with 2 degrees of freedom,

Castor wheel with 2 degrees of freedom,

Swedish 45 and 90 degrees or Omnidirectional wheel with 3 degrees of freedom, and

Ball or spherical wheel. These are omnidirectional also but fairly difficult to implement.

5.3.1.1 Standard and Caster wheels

Standard and Castor wheel are easy to implement. They have high load capacity and very high tolerance to, if there are any, ground anomalies. The high load capacitance and resistance to irregularities makes it a good pick for Knight Gear; however, these are not omnidirectional. In order to achieve some sort of directionality, the steerable wheels must be steered along the vertical axis and move around the horizontal axis. The configuration is easy to implement but when there is a high load then this method does not work. The vehicle does not move and causes high friction, increases the power consumption and reduces the accuracy of localization of the vehicle. Therefore, such wheels may not be the optimal choice for Knight Gear.

5.3.1.2 Swedish wheels

Swedish wheels are like normal wheels except that it offers low resistance to ground irregularities. Wheels run smooth in any direction. The rollers connected to the surface of the wheel are passive. In addition, the only actively powered joint is served by its primary axis. The advantage of this type of configuration is that wheel can kinematically be in motion with very little friction along the ground and many other trajectories.

5.3.1.3 Spherical or Ball wheel

These are omnidirectional wheels. There are numerous ways in which spherical wheels can be implemented to Knight Gear. One of these was invented by West and Asada in 1997 as shown in the figure 6 in the next page.

18

Figure 6 – Omnidirectional Wheels Permission Pending

In this design, power is transmitted from gears to roller right and then to the ball through friction between the roller and the ball. The ball rolls passively in any direction because the rollers are fixed at the roller right chasis and are actively powered.

Like it is explained above that the wheel type and wheel configuration are tremendously important. They influence the fundamental characteristics of:

Stability,

Maneuverability, and

Controllability

5.3.2 Characteristics of Wheels

5.3.2.1 Stability

Stability is a major concern when it comes to mobile robots. Knight Gear should not lose balance while following its user regardless of moving in smooth or rough surfaces. In order to gain stability, a minimum of 2 wheels are required. In some of the configurations, these vehicles attain stability when the center of mass of the vehicle is underneath the wheel axle. In other configurations, wheels are required to make ground contact to accomplish static stability. Knight Gear will have 4 wheels; this will give enough support and balance to achieve optimum stability.

19

5.3.2.2 Maneuverability

Maneuverability is also a very crucial aspect of Knight Gear. An omnidirectional robot has the ability to move in any direction. Such movement is actively powered by its omnidirectional wheels that can move in more in more than 1 direction like Swedish wheels. Vehicles using Ackermann steering configuration have turning radius that is larger than the vehicle itself. As result, it is unable to move sideways. These require a combination of changes in wheel direction of forward and rear wheels to produce movement. Robots and vehicles using such steering and wheel configurations are comparatively cheaper than having omnidirectional wheels.

5.3.2.3 Controllability

Controllability is inversely proportional to maneuverability. Vehicles with high controllability will have low maneuverability. The omnidirectional wheel‟s configuration allows vehicle to achieve very high maneuverability, however this strength of the robot makes it convoluted to control the robot. For instance, in Carnegie Mellon‟s Uranus robot all four wheels are to be driven at exactly the same speed in order to provide locomotion in precisely a straight line. Even minute errors in the speed of the wheels result in deviation from the desired path. However, because this vehicle uses Ackermann steering configuration, the controllability of this robot is very straightforward and easy. Locking the wheels and only driving the motorized wheels result in a perfect straight motion. It is able to achieve same speed in all the four wheels because all of the wheels are connected to just one axis. Hence, the speed of an individual wheel will always be the same as others. Therefore, it‟s impossible to achieve optimum controllability along with maneuverability. One has to go down to strengthen the other.

5.3.3 Selecting a wheel configuration

From the research performed, wheeled robots are indubitably the better choice for Knight Gear than legged robots due to the following reasons:

Designing and implementation of wheeled structure is less complex than legged structure.

Standard designing techniques, control feedback systems, algorithm techniques and structural components are easily available for wheeled robots.

Wheels have faster response to a command. This is a major aspect of Knight Gear. Immediate response is necessary, to travel indoors or outdoors, with respect to user‟s localization and time.

Percentage of error is higher in legged robot. Therefore, it is not the most efficient choice for Knight Gear.

20

Legged robots consume very high amount of power when compared to wheeled robots.

Once it is decided to use wheels over legged robots, it is important to choose which type of wheels to use for Knight Gear. Usually for a locomotive robot, most of the researchers and past projects have decided to go with omnidirectional wheels because they can carry the robot to any direction. However, standard wheels or caster wheels are more suitable for Knight Gear. Although, these wheels do not travel in all direction; but steering can be configured to reach out in all directions. Standard wheels make an optimal choice for Knight Gear because of the following reasons:

It is very easy to implement with all the available components.

The feedback from the standard wheel is higher than Swedish wheels and omnidirectional wheels for rotational directional change.

The change in speed will not affect Knight Gear directly.

If omnidirectional wheels were chosen, convoluted algorithms and calculations would have been needed to fulfill Knight Gear‟s need. Whereas, algorithms for standard wheels are not that complex.

5.3.4 How to Obtain Locomotion

There are several mechanisms to provide locomotion that is required for the Knight Gear. These driving techniques are the following:

Differential drive,

Ackerman steering,

Synchronous drive, and

Omnidirectional drive

5.3.4.1 Differential Driving

In differential driving, wheels rotate at different speeds when turning around the corners. It is very similar to „tank-type‟ steering but should not be confused with tank treads. Differential driving controls the speed of individual wheels to provide directionality in robot. The figure 7 on next page shows how changing the speed offers directional motion to robots. Correction factor is also need to be added to motor speed in order to fix the possible error that may occur due to difference in number of rotations of each wheel. The figure below shows how direction can be achieved in the robot. According to robotplatform.com –

“if the angular velocities are identical… then the robot tends to spin around its vertical axis. This compete turn capability is one of the greatest advantages of a differential driven robot.”

21

“if the angular velocities are identical in terms of values and opposite in direction, then the robot is more likely to follow a linear path, either forward or backward based on the motors spin.”

“if the angular velocities are different in terms of values (same or different direction), then the robot makes a cure motion.”

Figure 7 – Differential Drive Permission Pending

5.3.4.2 Ackerman Driving

Ackerman steering, displayed in figure 8, is a configuration that is used in cars today. This configuration includes two motors: one single motor drives the wheels and another motor controls the steering. According to robotplatform.com, the merits of Ackerman steering is increased control, better stability, and maneuverability on road, less slippage and less power consumption. The turning radius of this type of configuration may cause the robot to skid but the inner tire turns with greater angle that the outer tire avoiding any tire slippage.

22

Figure 8 – Ackerman Steering Technique Permission Pending

5.3.4.3 Synchronous Driving

In this technique, one motor synchronously actuates all the wheels and other motor defines the speed of the vehicle. As shown in figure 9, the second motor controls the speed and steering of all the wheels. This happens to be the best design possible for even surfaces. It can be implemented with 3 or 4 wheels; more the wheels, more the design and algorithm complexities of robot‟s motion analysis. Figure below shows how it can be executed by connecting wheels by a single drive and steer belt to the motor.

23

Figure 9 – Synchronous Drive Technique Permission Pending from Robotplatform.com

5.3.4.4 Omnidirectional driving

Omnidirectional driving can be achieved by using Omni wheels and/or Caster wheels. Omni wheels are consists of small and big wheels. Small wheels are hooked up perpendicularly to the inner circumference of the bigger wheel. This allows the wheel to move in any direction almost right away. One of the key merits of omnidirectional driving is that wheels do not rotate or turn to move in any direction. They are able to move in any direction without changing the orientation. Omni wheels are available is various varieties and coordinates as shown in figure 10.

24

Figure 10 – Omnidirectional Driving Permission Pending

5.3.5 Mechanical design of wheeled robots

After choosing what type of locomotion to choose, what type of wheels to use, building the frame for wheels is itself a very important task. There are certain features that should be taken care of while building the frame for Knight Gear. These features include appropriate configuration and orientation of wheels and correct procedures to achieve required motion.

1. Weight of Knight Gear – Most of the times the weight of the robot is mainly due to the type batteries using, the motor system and mainly the weight of the chasis and frame itself. The robot must maintain the optimal weight to offer desired motion.

2. Arrangements of components – The inclusion of sensors, motors, circuits, and other components must be compatible with the frame of robot. It has to be wheel structured so, it doesn‟t disturb the stability of the Knight Gear.

25

Here are several of the wheeled configurations available for a robot shown in Table 3:

Wheel Configuration Illustration Description

Static unstable two-wheeled

The front wheel allows controlling the orientation i.e. steering and the rear

wheel drives the vehicle.

Static stable two-wheeled

If the center of mass is below the wheel axle, this type of wheel achieves stability. The desired speed is achieved by changing the speeds and directions of the

wheels.

Differential drive with a castor wheel

The center of gravity should be maintained within the triangle formed by the ground contact

points of the wheels.

Tri-cycle drive, front/rear steering and

rear/front driving

The drive wheels are at the rear of the robot. A differential allows the vehicle to avoid the mechanical

destruction.

Tri-cycle drive combined steering and

driving.

The front wheel is used for both driving and steering. The two wheels in the rear keep the

stability of the robot.

Synchronous drive wheel

The synchronous drive system consists of a two motor drive

configuration. One motor rotates wheels and another motor

changes direction.

26

Front driven/steered Ackerman steering and

Front steered/rear driven Ackerman

steering

The difference of these two mechanisms is similar to the three

wheel system mentioned previously.

Omnidirectional

By changing the rotational speeds and directions of each drive the

required locomotion can be achieved.

Table 3 – Wheel Configurations

5.3.6 Braking Systems

Many of the motion done by the robot Knight Gear are done with the purpose of following its target. But there will be times when the robot will need to do a sudden stop or need to not move. When implementing DC motors into Knight Gear, the action of braking can be established with three different methods. It can be either done mechanically, electronically, or through coding. All three will be explained and one will be chosen as the appropriate method for braking in Knight Gear.

5.3.6.1 Mechanical Method

The mechanical method of braking is one of the most common seen today with large automobiles. This method involves using a very high amount of friction on the axel or wheel to stop the robot from moving. Equivalence to this would be a brake pad on a vehicle pushing against the drum of the wheel. The downside to this method is that it would be purely mechanical and would take time to implement this properly so it works every time.

5.3.6.2 Electronic Method

The electronic method of braking in a robot is one that varies depending on the motor. This method requires that the power be shorted and the ground be connected to the ground. Certain motors will break easier than other when shorted out. The motor will still continue to rotate, but it will also oppose the rotation toward the direction of movement. Although it could be unreliable because it all depends on the motor, it is simple to implement. This method is

27

viable when cost needs to be kept at a minimum because no extra parts are needed.

5.3.6.3 Coding Method

The coding method for braking is the last of the three methods for implementing a braking system in a robot. It is the most accurate method for completely stopping the robot in place. The implementation of this method requires some coding and knowledge of the current velocity of the robot. By finding out the current velocity of the robot, a signal can be sent to the motor controller to make the motor turn in reverse until the velocity of the robot is zero. Although it could become tedious to check the velocity every time the robot has to stop, it can make the stop more stable no matter where it is positioned. Whether it is on a flat surface, or an incline, with this method the robot can fully stop anywhere.

In conclusion, the coding method is the one chosen to implement into Knight Gear for the braking system. Since it is the only one that requires no extra components, and since it purely coding, it will be much simpler to implement than a brake pad or an extra switch.

5.4 Battery

5.4.1 Types of Batteries Knight Gear needs to operate freely without power supply wired from the walls. Thus the batteries are needed to be installed to provide enough power for all the electric components inside the robot to work properly. The elements that consume most of the power are microcontroller, dc motors, sensors, motor controller, and vision system. Following Table 4 summarizes the approximation of the voltage and current consumption from each component of the Knight Gear.

Devices Voltage Consumption Current Consumption

Microcontroller 5-9V 15mA

Motor controller 5V 15mA

DC motors 3-6V 500mA(x4)

Ultrasonic Proximity Sensor 2.5-5.5V 3.0-3.5mA

Infrared Proximity Sensor 2.5-6V 50mA

Weight sensor 9V -

Vision System - 50mA

Total ~2100mA

Table 4 – Approximation of the voltage and current consumption

28

From the approximation above, the DC motors consume the majority of current and the batteries of the Knight Gear need to provide at least 9V of voltage and 2100mA of currents. There are several different types of batteries that might use for the Knight Gear. The batteries are classified into two broad categories by its re-usability. The primary batteries (disposable batteries) are designed to be used once and discarded, and secondary batteries (rechargeable batteries) are designed to be recharged and used multiple times. For Knight Gear, our group decide to go with rechargeable batteries instead of ones that can‟t be recharged because the idea that we are interested in solar powered battery charger. Also, the primary batteries that require constant replacement might pose to be costly due to the amount of trials we intend to run causing it to potentially be very expensive in the long term. Thus, buying a rechargeable battery might seem more expensive in short term; it is much more cost effective in long term of use than the primary batteries. There are many different kinds of rechargeable batteries with different technology in the market, however only several that have affordable price and proper size for the Knight Gear will be discussed.

5.4.1.1 NiCad (Nickel Cadmium)

The nickel-cadmium or NiCad is a rechargeable battery that uses a nickel oxide hydroxide and metallic cadmium as electrodes. The NiCad batteries are good for small to medium size of robots like Knight Gear. They provide higher current output, and are more affordable than NiMH, and can be recharged within 2 hours.

For a common AA size cell, the maximum average discharge rate is about 1800mA, and the nominal cell potential is 1.25V. Another advantage is that they are easy to store and don‟t damage under most normal circumstances. Also low temperatures do not usually affect the NiCad and it has a good load performance meaning that it accepts the charge on the first try. This makes the Ni-Cad a good choice in any type of climate setting.

However, the NiCad battery does contain toxic metals that are considered environmentally unfriendly. This means that if this batteries are used in Knight Gear, each battery must be removed before the equipment can be disposed of in a landfill or recycle center. Because of these toxic metal issues, some countries are limiting the use of this type of battery, which insures it will be harder to dispose of older used ones in the future. A memory effect is another big disadvantage of the NiCad batteries. When a NiCad battery has been charged a certain amount of times, eventually the battery starts remembering its maximum charge is something that it actually is not. That is to say the battery says it is 100 percent charged, but actually it is only 80 percent charged. Thus, over the many recharging process, the battery can only store less and less power after each

29

charge. This memory effect could be prevented if the battery is recharged fully before its use. The NiCad batteries have flatter voltage vs time curve during discharge, as it can be seen in figure 11. Therefore, the voltage is more the less the same during the discharging process. However this method can‟t be fulfilled because the Knight Gear will use the solar powered battery recharging system that fully recharging the batteries at all the time is almost impossible.

Figure 11- Ni-Cad discharge rate Permission Pending

5.4.1.2 NiMH (Nickel Metal Hydride) Nickel Metal Hydride or NiMH batteries are another type of rechargeable battery. The technology used in NiMH is very similar to the nickel cadmium battery (NiCad). The NiMH use positive electrodes of nickel ox-hydroxide like the NiCad, yet the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH battery can have two to three times the capacity of a similar size NiCad, and their energy density come close to that of a lithium-ion (Li-ion) battery.

For a common AA size cell, the maximum discharge rate is about 1100mA to 2800mA, and the nominal cell potential is 1.25V. A complete discharge of this type of battery to its polarity can cause everlasting damage. Similar to the NiCad batteries, NiMH are not expensive and have the light weight. Another big

30

advantage of NiMH is that they have no problem with memory effect that NiCad batteries have. Also they don‟t contain any toxic materials. Thus they pose less environmental hazard for its disposal than that of NiCad batteries. However the NiMH batteries are comes in various capacities. Therefore it is necessary to check to be sure that the battery has the right capacity for the Knight Gear to operate properly. Also, the battery with high capacity might not charge completely in some battery charger. Another disadvantage of NiCad is that they have short shelf life. That is to say if the battery is not in use for two to three months, they self-discharge at a rate up to 25% per month. The discharge rate is heavily related to the temperature, the rate increases as temperature goes high. Thus, with steamy hot weather in Florida, self-discharge rate would be poor. Moreover, compare to alkaline batteries, the NiMH have slightly less voltage just like NiCad.

5.4.1.3 Alkaline Alkaline batteries are available in both primary and secondary types. The Alkaline uses the manganese dioxide as positive electrodes and zinc powder as negative electrodes. Similar to NiMH and NiCad, Alkaline batteries are inexpensive, light weight, and have small size. The common AA size cell, the maximum discharge rate is about 700mA and the nominal cell potential is about 1.5V. This is one of the benefit that rechargeable alkaline provide more voltage than NiMH and NiCad. Another advantage of Alkaline over the NiMH is that it loses the charge gradually that gives the notice when to recharge the batteries. The NiMH and NiCad tend to steep drop in voltage when they are in time to be recharged. Also, alkaline batteries do not contain the toxic metal and they can be disposable. Another benefit is that alkaline has very low self-discharge rate that it can hold the charge up to seven years. However, alkaline rechargeable batteries have big disadvantage that they have lower capacity compare to the NiMH. The capacity of an alkaline battery is heavily dependent on its load amount. Thus alkaline might have an adequate capacity about 2500mAh for low power devices but for the high power devices the capacity will be drop to as little as 500mAh. Moreover, alkaline can‟t be fully recharged. Each time recharges the battery; they lose some portion of their capacity. Therefore the battery has fewer recharge cycles (as few as 10 cycles) than NiMH battery. The discharge curve of alkaline battery is shown below in figure 12.

31

Figure 12 - Discharge rate of Alkaline batteries Permission Pending

5.4.1.4 Lithium-ion (Li-ion) A lithium-ion battery or Li-ion is another type of rechargeable battery. The Li-ion uses an intercalated lithium compound as the electrode material that lithium ions move from the negative electrode to the positive electrode during the discharge, and move back to negative electrode during the charging process. Unlike the batteries discussed above, the Li-ion batteries are quite expensive, and have various shapes and size. One of the advantages of Li-ion battery is that they have one of the best weights to energy ratio. Thus they are much lighter than other rechargeable batteries. Also the energy density of Li-ion is generally twice that of the standard NiCad. The load characteristics are reasonably good and behave similarly to NiCad in terms of discharge. The discharging curve of Li-ion battery is shown in figure 13.The high cell potential of 3.6V allows battery pack designs with only one cell whereas NiMH and NiCad require several cells connected in series to have that

32

potential. Moreover, Li-ion is a low maintenance battery that there is no memory effect and no scheduled cycling is required to maintain the battery‟s life. Also, the self-discharge rate is much less than the NiCad.

Figure 13 - Discharge rate of Li-ion battery Permission Pending

However, the Li-ion batteries are fragile and require a protection circuit to maintain the safe operation. The protection circuit must be built in the battery to limit the peak voltage of each cell during the charge and prevent the voltage from dropping too low on discharge process. Also, the cell temperature should be monitored to prevent the temperature extremes. The Li-ion battery is very dangerous compared to other secondary batteries because it could be erupted or explode in the high heat. Another disadvantage of Li-ion is that the life span is dependent upon aging from shelf life regardless of whether it was charged, and not just on the number of charge and discharge cycles. Also, as batteries age, their internal resistance rises. This causes the voltage at the terminals to drop below the load, reducing the maximum current that can be drawn from them. Eventually they reach a point at which the battery fails to operate frequently after two or three years. Another major disadvantage of Li-ion batteries is that they contain toxic metals and require disposal at a hazardous waste station.

33

5.4.2 Battery comparison and selection

As discussed above, there are four different types of batteries that are considered as the power supply of Knight Gear. The characteristics of those batteries are tabulated in Table 5 for us to make the best selection of the battery.

NiCad NiMH Alkaline Li-ion

Voltage (V) 1.25 1.25 1.50 3.6

Capacity (mAH) 600 ~ 1500 Depends on

brand

1200 ~ 2600 Depends on

brand

2000 At first use

2100 Depends on brand

Capacity load Low High High High

Recharge cycle 1000

if charged properly

500 ~ 1000 10 ~ 50 300 ~ 1000

Charging time (fast charge)

1 ~ 1.5h 2 ~ 4h 2 ~ 3h 2 ~ 4h

Charge/discharge efficiency (%)

70 ~ 90 66 Varied by

capacity load 80 ~ 90

Operating temperature (°C)

-20 ~ 45 -20 ~ 45 -20 ~ 60 0 ~ 45

Over charging tolerance

Moderate Low Moderate Very low

Disposal Not available Available Available Not

available

Self-discharge rate 10% / month 25%

<2%

8% at 20 °C

15% at 40 °C

30% at 60 °C

Memory effect Yes No No No

Price $ 5~7 $ 5 ~ 7 $4 $ 7 ~ 10

Table 5 – Battery Comparison

34

In conclusion, the battery selected for the Knight Gear is NiMH, because this battery has high capacity, no memory effects and environmentally friendly. Also, the NiMH batteries can be charged at any time without affecting battery life which is good characteristic for our solar powered charging system. For the Knight Gear, 9.6V 2100mA battery will be used as power supply of robot. A display of the battery that will be used is shown below in figure 14.

Figure 14 – This is a picture of NiMH battery that will be used to power Knight Gear

5.4.3 Recharging the Battery

5.4.3.1 Solar powered battery charging For Knight Gear, our group decide to go with rechargeable batteries instead of ones that can‟t be recharged because the idea that we are interested in solar powered battery charger. The reason that we are interested in solar powered charger is because the solar energy is becoming increasingly popular as the people begin to take notice the high cost of electricity and the seriousness of environmental pollution. Advantages of solar energy are that they don‟t produce any environmental pollution and generate electricity with no cost. Since there is no need of burning fossil to generate the electricity, solar energy is no harm to our environment. Also, the solar powered battery charger employs solar energy to supply electricity to

35

charge batteries therefore it is always free to charge the batteries whenever the sunlight is provided by the sun. On the other hand, some disadvantages of solar energy are that their initial cost will be very expensive, and they are only able to generate electricity during the daylight and no energy will be produced for about half of each day. However, considering the fact that the sun‟s light is readily available for free, this initial cost will be paid in a long term of use. In order to find the right solar panels for our project, some approximation should be made to get the solar energy power requirement. The energy stored in the NiMH battery pack is 9.6V * 2000mAh = 19.2W per hour. Thus if we select the solar panel that provide 5W per hour, then it will take at least four hours to completely recharge the batteries. Also, in order to connect the solar panels and the battery pack in parallel, Schottky diodes will be needed to prevent the batteries from discharging through the solar panel when there is no sunlight. The following diagram shows a simple schematic that possibly used for the connections between the battery and solar panels. The schematic of the solar panel is depicted below in figure 15.

Figure 15 – schematic diagram of the connection between battery and solar panels

After deciding on the amount of power needed to be drawn by the solar panels, we investigated on what type of panel to get. The material of the panel was important due to the different efficiencies of different materials in transforming

36

solar energy into electricity. There are several different types of solar panel in used today. Some of the solar panels suitable for Knight Gear were the following:

1) Monocrystalline 2) Polycrystalline 3) Amorphous

These types of solar panels were looked into in order to find the best match for Knight Gear. Monocrystalline Monocrystalline silicone solar panels are the most efficient type of materials to use for solar panels. These are one of the oldest and most sturdy ones. An extremely pure molten silicon produces the crystal of silicon, which eventually leads to monocrystalline silicon. These panels are one of the most efficient by having an efficiency of 13-17%. Monocrystalline solar panels have lots of empty spaces and since they are cut from a single crystal and rarely fill up a square solar cell module. However, since they are made with high silicon content they are more expensive than other materials. They also require extra time and energy to produce such photovoltaic cell. Polycrystalline In comparison to monocrystalline silicon, polycrystalline silicon are made from square cast ingots of silicon, they are also less expensive than their monocrystalline counter parts, but have a lower efficiency rate. As a result, one generally needs a larger polycrystalline solar panel to match the power output of a monocrystalline solar panel. These are also produced from extremely pure molten silicon however, using casting process. In the technique, silicon is heated at a very high temperature and then cooled down. This leads to a formation of poly-multi-crystal form. The silicon block is then cut into 0.3mm slices. The thickness of the anti-reflective layer determines the blue appearance of the silicon. It absorbs most of the sun light and reflects very little. Polycrystalline, like mentioned above, lacks in efficiency. The efficiency rate of such type of photovoltaic cell is 11-15%. Amorphous This type of solar panel is non-crystalline silicon. Amorphous solar panels are most found in calculators. The production process requires only few raw materials therefore, the layer of semi-conductor coating is only 0.5-2 micro meters thick. The film of amorphous silicon is deposited as a gas on a smooth surface. Chemical process takes place to finish the process. The efficiency of amorphous photovoltaic cell is only about 6-8%.

37

In the end we decided to use small monocrystalline solar panels to build our battery recharger for Knight Gear. Even though they are more expensive than polycrystalline panels, we feel that if we reduce the size we will minimize the amount of capital used to build this sub system. A picture of a monocrystalline solar panel can be seen in the figure below.

5.4.4 Wall Mount Battery Charger (optional) Although our group decides to use solar energy to recharge the battery, wall mount battery charger might be needed for the fast charging. As discussed above, when a 5W solar panel is used for recharging, it would take at least four hours to completely recharge the battery. Therefore, the waiting time for recharging could be a waste of time when we conduct the many tests for our devices such as sensors, motors, and microcontroller. Thus, using a wall mount battery charger would shorten the time it takes for the testing process. Moreover, the solar panels are only able to generate electricity during the daylight and no energy will be produced for about half of each day. Also, there are times when cloud cover obscures the sun and the efficiency of solar panels drops. Therefore wall mount battery charger is optional but should be needed for the Knight Gear. The following picture is a candidate of the wall mount battery charge from Tenergy that will possibly be used for the optional charging method of power supply for the Knight Gear. The battery pack that will be used in the execution of knight gear is exemplified below in figure 16.

Figure 16 – Tenergy Smart Universal NiMH/NiCD Battery Pack Charger: 6V-12V

Reprinted with permission

38

5.5 Power Transmission 5.5.1 Power distribution and regulation Although we have a battery pack that provide sufficient voltages for every electric devices on the Knight Gear, power regulation circuit must be implemented to regulate this input voltage. In the Knight Gear, different electronics require different voltages. For instance, when microcontroller requires 5V, the gear motors require 9V, and several of sensors require different voltage as well. Thus if we connect the battery directly to the every devices, it would damage the circuit and the robots would fail to work. Moreover the batteries are never at a constant voltage that the electronic devices which are sensitive to the input voltage and operate correctly only within a certain narrow voltage range such as microcontroller and sensors could be damaged from it. Therefore the voltage regulation circuit must be implemented to prevent such problems. The voltage regulator is designed to maintain and provide constant voltage level for the devices. The most commonly used methods for the voltage regulation are using the linear and switching regulators. Switching Regulator In a switching regulator, transistors are turned completely on or off like a typical switch. When they are on lots of current can flow but there is almost no voltage across the transistor therefore the transistor dissipates very little power. When the transistor is off there is usually a voltage across the transistor but there is no current so again there is very little power. Energy is usually stored and filtered through inductors and capacitors and regulation is controlled by varying the percentage of time on versus off. The advantage to this is that if there is very little heat or wasted power, making this design capable of being very efficient. However, disadvantages of switching regulators are that they are more complex to implement than the linear regulator. They usually require inductors, transistors and filters for the circuit design. Switching voltage regulator processes by taking small loads of power, which comes from input voltage and then is redirected to the output. Switching regulators undergoes a process where an electric switch is used and a simple controller regulates the flow of energy, which is then transmitted to the output. There is very little amount of heat that is wasted in such type of regulator, which is why this is more efficient between the two types of regulators. It can achieve upto 85% of efficiency. In addition, the efficiency is less dependent on the input voltage. Therefore, it can power big loads from input voltages. Switching voltage regulators are ideal high efficiency is required. For instance, these can be mobile devices, digital cameras and computers.

39

Although switching regulator provides great efficiency rate, it fails to simplify the implementation of design. These regulators are very convoluted. It incorporates a complex design circuit, which makes it, slightly, unwanted among beginners. Switching regulators empowers any other regulators when it comes to moving more than 200mA of load at high input voltages. Linear Regulator On the other hands, in a linear regulator, the transistor is turned partly on so as to provide the proper resistance to the load, thus the load always sees the same voltage. Since it is partly on, there is a definite voltage drop across the regulating transistor and there is as much current simultaneously as the load is demanding. Therefore power is being dissipated across the transistor which turns into heat. This heat is wasted power and the reason that switching regulators are more efficient than the linear regulators. Linear regulators are easy to use and are not very expensive. The process of linear regulators undergoes taking the difference between the input voltage and output voltage. This difference between voltages is directly proportional to the heat generated by the linear regulator. Hence, larger the difference between input and output voltage, the more the heat voltage regulator generates. As a matter of fact, some of the linear voltage regulators waste power during stepping down voltage than what it actually ends up providing to a particular device. Efficiency of a linear voltage regulator is about 40%. Linear regular is not very efficient. Therefore, it can go as low as 14%. This inefficiency causes lot of wasteful heat that needs to be dissipated through large and expensive heatsink. This also causes a danger to the device‟s battery life. There are several ways of determining which type of regulator, switching or linear, is suitable for Knight Gear. From the research done, it turns out that if the linear voltage regulation wastes less than 0.5W of power, then a switching regulation is not worth a try, given that it would go through the convoluted circuit design to improve the efficiency and its relatively high price is not ideal if the waste is less than 0.5W or power. While on the other hand, if the waste through linear regulation process is more than 0.5W then switching regulation is almost a must. The equation below can be used to calculate the wasted power in a system. However, considering that the Knight Gear is operating at low voltages and the heat waste will not be very critical, our group decides to go with the linear regulator for the power regulation system. Some of the criteria of the regulator that are needed to be considered for our project include type and range of the applied input voltage, required output voltage, maximum load current, minimum dropout voltage, quiescent current, power dissipation, and shutdown current.

40

5.5.1.1 Texas Instruments Model LM2941 The Texas Instruments model LM2941 is low dropout voltage regulator. A regulator‟s dropout voltage is the voltage required between the input and the regulated output voltage. The LM2940, with a .5V of low dropout at 1 amp provide a regulated 5 volt output. Thus it is much cooler than the regular linear regulators. Some other low dropout voltage regulators will also be used to regulate the output voltage to 9V or 6V. The schematic of LM2941 is shown below in figure 17.

Figure 17 – Typical application of Texas Instruments model LM2940 Reprinted with permission

5.5.1.2 Linear Technology Model LT3014 This model is another low dropout voltage regulator that provides wide range of input voltage from 3V to 80V with dropout voltage of 350mV. Advantage of this model is that output voltage can be adjusted in a large range from 1.22V to 60V. Also no extra diodes are needed for this model thus implementation is much easier. Disadvantage is that output current is only 20mA which is smaller than some devices‟ current requirement. The schematic of LT3014 is shown on next page in figure 18.

41

Figure 18 – Typical application of Linear Technology model LT3014 Reprinted with permission

5.5.1.3 LM7809 Linear Regulator A 9V voltage regulator is needed to regulate high voltage coming from battery, which will be used to charge the devices. 9V LM7809 will supply inductive charging to Knight Gear. LM7809 linear regulator offers output current up to 1A and fixed output voltage from 5V to 24V. It also offers thermal overload and short circuit protection. The figure 19 below displays the schematic of LM7809 9V linear voltage regulator.

Figure 19 - Schematic of LM7809 Reprinted with permission from Texas Instruments

42

5.5.1.4 LM7805 Linear Voltage Regulator LM7805 uses a 5V linear voltage regulator. The three terminal L7805 linear voltage regulator is an ideal regulator for Knight Gear due to 5V output signal. According to the datasheet of this regulator, two capacitors will need to be implemented for filtering. One of the capacitors is 0.33µF and other is 0.1µF. The 0.33µF is placed in parallel with the input voltage of LM7805 regulation. This particular capacitor will filter out any noise engendered from the voltage sources. The 0.1µF will also be placed in parallel to the output voltage of LM7805 regulation. This capacitor will reduce any noise generating from high frequency alternating current. Together, both of the capacitors will provide a clean signal of 5V. A schematic of LM 7805 is shown with the two capacitors in figure 20.

Figure 20 - Schematic of LM7805 Reprinted with permission from Texas Instruments

5.5.1.5 PTH0407W Switching Voltage Regulator PTH0407W is a voltage regulation that is highly integrated and provides up to 3A of current at very low price. The advantage of this voltage regulator is that it requires less man hour work and cost of printed circuit board (PCB) design. It provides an output current at much higher efficiency and at low waste of heat. The input voltage varies from 3V to 5.5V. The switching regulator allows to step down the voltage to as low as 0.9V to 5V with about 1W of dissipation of power. Furthermore, the output voltage varies from 0.9V to 3.6V with a resistor. PTH0407W switching voltage regulator incorporates on/off function. It also offers an under-voltage and over current protection system. Schematic of PTH0407W is shown on next page in figure 21.

43

Figure 21 - Schematic of PTH0407W

Reprinted with permission from Texas Instruments

Pin 5 of this regulator is the on/off inhibitor. It sets the output voltage to be turned off from this switching regulation. The product performs ideally when inhibit pin is opened. Use of a transistor is preferred and it applies low voltage to the inhibit control pin 5, when it is turned on. During the power up, internal “soft-start” circuit slows the rate of the rise of output voltage. Therefore, it reduces the current drawn from its input source. This “soft-start” circuit broaches a short time delay of 10ms. This is where a valid input source is recognized. Figure 22, shows the power up rise from an input voltage of 3V and output voltage of 1.8V and measured current of 2A.

Figure 22 - Power up waveform

Reprinted with permission from Texas Instruments

44

Any fault that may exist that could potentially limit a system‟s capability in a system is protected by the output overcurrent protection system. This protection system does not allow PTH0407W to except the limited current value. Any attempt to increase current beyond this limitation will cause reduction in the output voltage. Current is supplied until the fault is completely removed from the system; and once it is removed, the output voltage is restored in no time. The efficiency of PTH0407W against the output current is shown below in figure 23.

Figure 23 - Efficiency of PTH0407 at various given output voltage

Reprinted with Permission from Texas Instruments

5.5.1.6 DE-SW050 Switching Voltage Regulator DE-SW0XX is a family of switching voltage regulators that is very simple and very easy to integrate in a system. DE-SW050 offers the end user to take a load of up to 30V from a high input voltage and compress it to 5V in very efficient way. The efficiency of this voltage regulator is 83% and can reach to 87%, if used wisely. Another great advantage of this regulator is the already integrated decoupling capacitors. The following image in figure 24 is the relative size and shape of DM-SW050 switching regulator.

45

Figure 24 - Relative size and shape of DE-SW050 Permission Pending

Although, it is relatively bigger in size when compared to other linear voltage regulators however the efficiency it generates is good enough to disregard the larger dimensions of this switching voltage regulator. The graph in figure 25 shows the efficiency against the input voltage

Figure 25 - Efficiency of DE-SW050 switching voltage regulator

Permission Pending

46

5.5.1.7 Linear Technology Model LT1121 This low dropout voltage regulator also provides large range of input voltage from 3.75Vto 30V with dropout voltage of 400mA. Output voltage can be adjusted from 3.3V to 5V which is very suitable for our project. The schematic of LT1121 is shown below in figure 26.

Figure 26 – Typical application of Linear Technology model LT1121 Reprinted with permission

These are some candidates of the low dropout linear regulators that will possibly be used in the design of our power supply for the Knight Gear. Since our battery will provide 9.6V, this source voltage will be converted to the subsystems at voltages of 9V, 6V, and 3V by using the low dropout voltage regulators. The following diagram on the next page shown in figure 27 represents the overall concept of the power supply system that will be used for the Knight Gear.

47

Figure 27 – Block diagram of power supply system of Knight Gear

5.6 Motors 5.6.1 Types of Motors For the Knights Gear to move along the user it is necessary to decide on what kind of motor to use. As specified in the requirement part of the report, four DC motors will be used for the Knights Gear. The reason we choose DC motors instead of AC motor is because our robot is powered with direct current (DC)

48

coming from batteries and the electric components in the robot also uses DC. Thus, it is more convenient to have the same type of power supply for the motors. Also, the reason we choose four motors is because it makes the robot easier to position and control. Some of the criteria of the motors that are needed to be considered for our project include RPM, torque, and ability to operate in both clockwise and counter-clockwise direction, and minimum voltage and current need. There are several different types of DC motors that are commonly used in four wheeled robots. The three kinds that are considered are DC motors, stepper motors, and servo motors. DC motors are very simple, inexpensive, small and powerful. Also their speed can be controlled easily by varying the source voltage. However, their torque is not strong enough to move the robot with heavy loads. Thus, gear-train reductions are needed to reduce the speed and increase the torque output of the motor. Since the Knight gear should follow the user carrying at most 50lb of loads, it requires large torque with moderate speed about 3 ft/sec. The DC motors are available in brushed, brushless, stepper, and servo. There are several key differences between the different technologies.

5.6.1.1 Brushed DC motor Brushed DC motors depend on a mechanical system to transfer current, while brushless dc motor use an electronic mechanism to control current. The brushed motors have a wound armature attached to the center with a permanent magnet bonded to a steel ring surrounding the rotor. As the brushes come into contact with the rotary electrical switch, the current passes through to the armature coils. The common brushed dc motors that use for robotics have the RPM range from 5000 to 10000 which is very high rotation speed compare to others. One of the advantages of the brushed motor is that it is very easy to control and motor controller is not necessary when the robot just needs a constant speed. All we have to do is just vary the supply voltages to the motor to control its speed. Also, brushed DC motors are very inexpensive compare to other motors. However, the brushes inside the motors can be wear out very quickly and require replacement and, also the commutator itself is subject to wear and maintenance is highly needed. Noise problem is another drawback of the brushed DC motor, at the higher speeds, brushes inside the motor have increasing difficulty in maintaining contact and causes imperfect electric contact and the noise. For the Knight Gear, there are four motors will be installed, thus the noise produced by each motors will be very noisy and unpleasant for its user.

49

5.6.1.2 Brushless DC motor Unlike the brushed motor, brushless DC motors uses an electronic mechanism to control the current. They use a magnet, driving coils and sensors that sense the position of the rotor to rotate the motor. In brushless DC motor, there is no contact inside the motor due to absence of brushes. Thus, compare to the brushed DC motor, less maintenance is required and less noise is generated. Also, speed range is much higher than the brushed motor because there are no mechanical limitation imposed by brushes and commutator. Moreover, the heat dissipation is not high because its internal rotor construction is different and more efficient compare to the brushed motor. However, the motor controller is required in order to control the brushless motor. Since there is no physical contact inside the motor, it is hard to know when and where the current should be applied. Therefore it is indispensable to get a separate electronic motor controller if the brushless motor is used in Knight Gear. This requirement poses much higher cost for the brushless motor. Although brushless DC motor have higher price and require complex controls, compare to the brushed motor, brushless DC motors are very widely used in robotics because they have longer life, higher efficiency, less maintenance, low electrical noise generation and other good characteristics

5.6.1.3 Geared DC motor

Since the torque generated by a brushed or brushless DC motor is too small and the speed is too needlessly high, gear reductions are usually used to reduce speed and increase torque. If we choose either brushed or brushless motor for the Knight Gear, it would be better to buy the product which already has the gear reduction system. Geared DC motor is a bigger, more powerful version of DC motor that gear reducer is integrated. The geared DC motors are very often used in robotics and other control situations where a small motor with lots of power is needed. The speed is generally controlled using pulse width modulation of the fixed input voltage. Like other DC motors, geared DC motor can operate in both clockwise and counter clockwise and its speed can be altered by varying the voltage applied to the motor. Input voltages range of the motor used for robotics range from 3-30V. However, if we buy the new geared dc motors, it is very expensive compare to the motors without gear train, and if we buy the old one, the gear train might get noisy and the gears could go bad. Although geared dc motors are quite expensive, it would be the only choice if we buy the brushed or brushless DC motor for the Knight Gear unless we manually build the gearing system by

50

ourselves. Figure 28 depicts image of motor that will be used to drive Knight Gear

Figure 28 – This is the Geared DC Motor that will be used in Knight Gear.

5.6.1.4 Stepper motor

Stepper motor is another type of motor that could be used for Knight Gear. Unlike other DC motors discussed above, the stepper motor doesn‟t rotate continuously. That is to say, it only terns in small steps and in order to make it spin like other motors, we have to give power to the different parts of the motor in a specific sequence. Thus it is more complex to control the stepper motor than the regular DC motors.

Some advantages of stepper motors are that they don‟t require the gear reduction to control its speed and torque, and provide precise control of the position.

However, since the motor doesn‟t rotate continuously, they have poor performance on the uneven surfaces. Also, the stepper motors consume very higher current compare to other motors especially when they spin continuously. Moreover their complexity in controlling requires special driving circuit to provide the stepping rotation.

Although the stepping motors provide the shaft to rotate in the precise manner, their high consumption of current and unstable mobility on the various loads and complexity in controlling make our group to keep aloof from buying this motor for the Knight Gear.

51

5.6.1.5 Servo motor Similar to the stepper motor, original form of the servo motor does not spin continuously. That is to say, the original form of servo motors is used to move a shaft to a certain position between 180 to 270 degrees. Therefore they are originally used for controlling of the robot‟s arms, plane‟s wing and others where the precise angle is needed. . However, they can be modified for 360 degree rotation by changing their internal electronics. By doing this modification, the servo motor lost its position control function but gain the speed control function. Advantages of the motors is that they are available in various sizes and come with standard mounting holes that make us easy to mount on the Knight Gear. And after the modification, servo motors need only one output pin for interface, and don‟t need an external motor controller The drawback of the motor is that they need to be modified in order to function as spin motor which could be a risky work to do. Also, since they are originally designed for the position control motor, torque and speed is relatively low compare to other DC motors. Thus servo motor with higher toque and speed is very pricey. Although the servo motors can be controlled directly from the microcontroller and easy to mount for the Knight Gear, their price is high and required modification accompanies some risks. In conclusion, DC geared motor will be used for the four wheels of the Knight Gear. DC geared motor has higher torque operating under the low current, which can save the energy, and it is originally design as the continuous motor thus no modification is needed. Also, its price is relatively low compare to other stepper or servo motor. The spur type of gearing will be used because it is most common gear type that used widely in the robotics and their price is relatively low. The 6V DC spur gear motor will be used and its price is range from 12 dollars to 17 dollars.

5.6.2 Motor Controller

In order to control the motors in the Knight Gear, selection of the right motor controller is very crucial part for the project. Although the microcontroller can decide the speed and direction of the motors, they cannot be connected directly to the motors. Most of microcontrollers have some input and output pins that can be set to high (5v) to low (0V) under the software coding. However since their pins are only capable of supplying a very few mA of currents and the motors generally requires much more current and voltage to operate, input and output pins of microcontroller cannot be used for controlling the motor. On the other hand, the motor controllers are designed to provide the enough current and voltage to the motor but they cannot decide how fast the motor

52

should spin. Therefore motor controller and microcontroller need to work together to make the motors to move properly. Some of the criteria of the motor controller that are needed to be considered for our project are that it must be rated for voltage of our battery pack and it also must be able to handle the motor‟s stall current. Moreover, communication method between microcontroller and motor controller should be met. For Knight Gear, PWM will be used for the communication between the microcontroller and the motor controller. There are two different methods that can be used to build a motor controller for Knight Gear. First, we can build our own motor controller by using a small motor driver integrated circuit. One of the advantages of these circuits is that their price is very low. Their price is range from as little as 1 dollar to 5 dollars. Thus even if there are some mistake building the controller and this chip is burned, it is not a big loss for us buying just a new chip. Also, it is not very hard to get more current or heat dissipation out from the chip. If we buy the motor that require more current needed than a single IC can provide, we can just connect the IC chips in parallel to get more allowable current and heat dissipation. Only drawback of this circuit is that they are mostly used to handle two motors. Since the Knight Gear has four motors and each motor need to be controlled independently, at least two motor driver Ics will be needed for our project. Second, we can simply buy a finished motor controller product that is available in the market. One of the advantages of the finished motor controller products is that they already have a motor driver and some certain logics integrated in the circuit. Therefore the motor controller is widely used for the beginners who just want a plug and play to control their motors. Another advantage of the motor controller is that they provide some useful features for the users. Many of the motor controllers have H-bridge circuit that can be used to control the direction of each motor, and have on-board current and voltage monitoring system that prevent the over current problems. Moreover, some motor controller have built in charging system that they can charge the Li-MH or Li-CD battery using their on board current regulator. However, most of the motor controllers are way too expensive compare to the driver Ics. Their price is range from thirty dollars to as much as few hundred dollars. This is a very big drawback, because if this controller get damaged or failed during the trial, we have no choice but to buy the new expensive product again. There were four different driver Ics and motor controllers that are very capable for our project. At first, we have researched for four different products of both drivers IC and motor controller. However, since the price of finished motor controller product is way too expensive for our low budget project, the three different motor driver Ics will be discussed only, and then we will compare those three to select the best product for our project.

53

5.6.2.1 Texas Instruments Model L293D The Texas Instruments model L293D is a very popular motor driver IC that is widely used for controlling DC and bipolar stepper motors. This motor driver IC can either control two DC motors with individual directional and speed control, or four DC motors with just on and off. This model can support pulse width modulation control and has ability to handle a wide range of operating supply voltages from 4.5V to 36V and enough output current of 600mA for each channel. Also this model includes output diodes that no extra diodes are needed. Moreover, this model has standard pin packages for schematic design that makes easy to implement the circuit. Other features that are provided in this model include thermal shutdown, internal electrostatic discharge protection, and high-noise-immunity inputs. According to mouser electronics website, price of this model is $3.12 each. The schematics of L293D is shown below in figure 29.

Figure 29 – Texas Instrument model L293D Reprinted with permission

5.6.2.2 Texas Instruments Model SN754410 The Texas Instruments model SN754410 is another widely used motor driver IC that function very similar to the L293D model stated above. This motor driver IC can either control two DC motors with individual directional and speed control, or four DC motors with just on and off. This model also has ability to handle a wide range of operating voltages from 4.5V to 36V. This model can support pulse width modulation control as well. The SN754410 also has the protection diodes for running inductive loads as well but can provide more continuous current up to 1.1A. Although the model L293D has sufficient continuous current output of

54

600mA for the motor that we are already choose, model SN754410 could be used as replacement if we decide to use more powerful motors for the Knight Gear. According to mouser electronics website, price of this model is $1.87 each which is somewhat cheaper than the L293D model. As the diagram shows below, pin-outs of the SN754410 are exactly same as the pin-outs of the L293D model. Thus this model is direct plug in replacement of L293D model and the block diagram for the motor connection and state table is same as well.

5.6.2.3 Texas Instruments Model DRV8833 Another motor driver IC that we considered is Texas Instruments model DRV8833, which can be seen in the figure below. This model has dual H-bridge and is designed for driving two DC motors or one stepper motor. Each of the H-bridge includes circuitry to regulate or limit the winding current. Compare to other models stated above, this model has ability to handle small range of operating voltage that from 2.7V to 10.8V and provides less continuous current up to 500mA. This model can also support pulse width modulation control that will be used for the speed control. The DRV8833 also has the protection diodes for running inductive loads as well so no external diodes are needed. Other features that are provided in this model include under-voltage lockout and protection against over-current and over-temperature, reverse-voltage protection circuit and current limiting system if sense resistors are added. According to mouser electronics website, price of this model is $2.58 each. The functional block diagram of DRV8833 is shown on next page in figure 30.

55

Figure 30 – Texas Instrument Model DRV8833 Reprinted with permission

5.6.3 Motor controller comparison and selection As discussed above, there are three different types of motor driver Ics that are considered as candidates for the motor controller of Knight Gear. The characteristics of those Ics are tabulated below in table 6 for us to make the best selection of the motor controller.

56

Model L293D SN754410 DRV8833

Brand Texas Instrument/ Stmicroelectrics

Texas Instrument

Texas Instrument

Operating supply voltages

4.5V ~ 36V 4.5V ~ 36V 2.7V ~ 10.8V

Tolerant peak output currents

1.2A 2A 1A

Continuous currents per each channel

600mA 1.1A 500mA

H-Bridges Quadruple-Half Quadruple-Half

Dual

Control method PWM PWM I2C / PWM

Internal diodes YES YES YES

Price (from mouser electronic website)

$3.12 *2 $1.87 *2 $2.58 *2

Table 6 – Motor Ics comparison In conclusion, Texas Instrument model SN754410 will be used as motor controller for the Knight Gear. This model provides sufficient continuous current of 1.1A with lowest price thus this model seems very cost effective. Also, this model has standard pin packages for schematic design and no extra diodes are needed that makes easy to implement the circuit. The picture of SN754410 that is to be used for Knight Gear is displayed on the next page in figure 31.

57

Figure 31 – This is SN754410 motor driver that will be used in Knight Gear.

There are two different ways to use the SN754410 motor driver to control each motor.

4) 3 pin mode, or 5) 2 pin mode

Each has its advantages and disadvantages.

3 Pin mode

This requires one hardware PWM pin plus two general-purpose digital output pins per motor. The following diagram, in figure 32, shows how to make this 3 pin mode for SN754410.

58

Figure 32 – This is the schematic of 3pin SN754410 Permission Pending

The benefit of this mode is that it can support all the possible motor drive states such as forward, reverse, brake and coast. Variable speed is achieved by changing the PWM signal from the microcontroller. The following table 7 shows the truth table of motor function using the 3 pin mode.

PWM (1,2 EN and 3,4 EN)

Digital output pin

(1A or 3A)

Digital output pin

(2A or 4A)

Motor state

0 - - Coast

1 0 0 Break

1 1 1 Break

1 1 0 Forward

1 0 1 Reverse

Table 7 - Truth table of 3 pin SN754410 motor controller

2 pin mode

This requires one hardware PWM pin plus one general-purpose digital output pin. The following diagram shows how to make this 2 pin mode for SN754410 in figure 33.

59

Figure 33 – This is the schematic of 2pin mode for SN754410 Permission Pending

The drawback of this mode is that it doesn‟t support the „coast‟ motor drive state. Consequently to achieve variable speed settings the motor alternates between full speed and brake via the PWM pin. Although it only uses two output pins of microcontroller, it causes the motor under some stress and will wear out the motor more quickly than the 3 Pin-mode. The following table 8 shows the truth table of motor function using the 2 pin mode

PWM (1A or 3A)

Digital output pin

(2A or 4A)

Motor state

0 0 Break

0 1 Reverse

1 0 Forward

1 1 Break

Table 8 - Truth table of 2 pin SN754410 motor controller

Although the 2 pin mode require only two output pin of microcontroller, it will put some stress and wear out the motor fast. Thus, if our microcontroller has available output pins, 3 pin mode will be used for the motor controller of the Knight Gear.

60

5.7 Camera or Vision System

The vision system is not a requirement of the Knight Gear. However, it is a remarkable accessory to have in the system. The video system will be used to view the surroundings of the Knight Gear and comfortably follow its user. The vision system is not as critical as some of the other sensors like infrared, ultrasonic, gyroscope or accelerometer. This is because the vision system by itself is an independent system. It neither should depend on other system nor should it affect the capabilities of sensors, GPS module, driving, and steering of Knight Gear. The purpose of camera system is to provide vision to Knight Gear. In order to implement the camera system, it must meet the following specifications:

It must not weigh any more than 500 grams.

It must have a range of approximately 100 meters.

The operational current should not be any more than 500mA

A lot of research has been performed to execute this system. There are several ways though which such camera system be implemented. Few of these methods are:

Through an image sensor,

Through a webcam or camcorder, or

Through a prepackaged in-built video system. The image sensor is probably the hardest of the lot to implement. In this technique, everything is built around the image sensor through some extensive coding. In order to receive data, a transceiver is needed that has data rate and bandwidth to send the information or data wirelessly. In addition, the system needs a lot of power to compress and format the video, and send it to the transceiver. A minimum resolution of 640 x 480 is required by the image sensor to appropriately interpret the data. Such type of video system that uses image sensor has the potential to be least expensive but at the price of time. Building such a system is very time consuming. The image sensor comparison is shown on next page in table 9.

61

Image Sensors Resolution Image Senor

Size Frame Rate

MT9V024IA7XTC WVGA 1/3 inch 60 fps

MT9V024IA7XTR WVGA 1/3 inch 60 fps

MT9V032C12STC WVGA 1/3 inch 60 fps

MT9V032D00STC WVGA 1/3 inch 60 fps

MT9V034C12STC WVGA 1/3 inch 60 fps

MT9V034C12STM WVGA 1/3 inch 60 fps

Table 9 – Image Sensor comparison

Second method is to get the video from a webcam and construct the remainder of the system around it. This method lessens the work load that the first method, however this system is still quite challenging to build. A processing unit is still needed to compress, convert, format and send the video information wirelessly to a display unit. The issue with this type of technique is finding such processing unit that can use the raw video data and possibly convert it to a format and send it to the transceiver that is compatible to Knight Gear. Such type of video system is costlier than the first method but again, to build a video system using this method would require excessive time in hand.

The last method is to buy a prepackaged in-built video system for Knight Gear. This is the costliest of the all the methods discussed but is not time consuming. Such a video system incorporates a video camera, video transmitter and a video receiver, and is rather easy to implement. All it takes is simply mounting the package on the front of Knight Gear. This should allow Knight Gear to see the surroundings. Table 10, lists the two prepackaged system that were looked into.

Prepackaged System

Range Weight Price

24ghzmiwicoc 150 m 9 g $39.99

SFA-010256 100 m 1.3 kg $64.99

Table 10 – Prepackaged in-built video system comparison.

62

5.8 Sensors

5.8.1 Types of Sensors

Knight Gear utilizes multiple sensors to accomplish tracking and localization of the user and obstacles. The weight sensor is also used as a safety measure to verify that the load on Knight Gear is low enough to not burn out the motors equipped to it. The ultrasonic and infrared sensors are used to find the user and track the user along. Additionally the accelerometer and the gyroscope are used for localization and object avoidance.

5.8.1.1 Ultrasonic Proximity Sensor

Piezoelectric transducer is used to determine sound waves in ultrasonic proximity sensors. It engenders high frequency sound waves (above 20,000 Hz), which is incorporated in these sensors, to measure the echo encountered by the detector, and is then received after reflecting back from the target. Ultrasonic sensor plays an indispensable role in Knight Gear. Some of the key advantages of ultrasonic sensors are as follows:

No physical contact is needed with the object that is to be detected. Thus, the target for the sensor will be attached to the back of the belt or hook of the user. The sound waves will exude from the emitter to follow and find the target, and returns back to the detector. Having a wide range is essential for the sensor because the user will be in motion.

Since there is no mechanical contact with the target, the numbers of operating cycles are unlimited.

Ultrasonic proximity sensors will work regardless of the target‟s color, atmospheric dust, rain, snow, reflecting and metallic surfaces or any repugnant conditions.

It provides resistance to external disturbances such as vibration, noise, and infrared lights.

Having said some of the vital benefits of ultrasonic proximity sensor to Knight Gear, these are not ideal. There are limitations to accuracy when dealing with target that is not perpendicular in respect to the sensor. Another major issue of ultrasonic proximity sensor is when sound waves reflected off the walls in strange pattern creating ghost echo. Noise issues are also to be taken into account while using multiple sensors.

Numerous types of ultrasonic proximity sensors are taken into account when it comes to selecting the best for knight gear. These were LV-MaxSonar EZ series, XL-MaxSonar EZ/AE/WR series, HRLV-MaxSonar EZ series, and HRXL-MaxSonar WR/WRC series from MaxBotix. All the ultrasonic sensors that were looked up during the research in order to pick the best fit for Knight Gear are listed in table 10 with its specifications. From all these possible choices, LV-MaxSonar-EZ (EZ0-EZ4) fulfills the general need of distance sensor of Knight

63

Gear. According to MaxBotix website LV-MaxSonar EZ are “low cost ultrasonic distance sensors to provide a component module solution that offered easy to use outputs, no sensor dead zone, calibrated beam patterns, stable range readings, low power demands, and a host of other feature”.

Now, within the LV-MaxSonar EZ (EZ0-EZ4) series, the beam width gets narrower and sensitivity get lower as progressed from EZ0 to EZ4. LV-MaxSonar EZ0 provides most of the same characteristics as EZ1, EZ2, EZ3, and EZ4 except that it has widest beam width and most sensitive beam pattern of all. Wider the beam width, the better it is for people detection. However, this also results in more noise and ghost echoes. Detection angle and detection pattern is crucial while deciding which type of sensor to use. Figure 34 and Figure 36 provides a good illustration of the detection pattern of EZ0-EZ4 and detection angle of EZ1 respectively. Figure 35 shows the PCB layout of EZ series. A graphic representation of detection angle of EZ2 was not available, but from the model of EZ1 an idea of beam pattern can be attained. Table 11 below lists all the ultrasonic products that were looked into.

Products Resolutio

n Reading Rate

Maximum Range

Required

Voltage

Required

Current

Operational Temperatur

e Price

XL-MaxSon

ar-EZ 1cm 10Hz

300in-420in

3.5V-5.5V

3.4mA 0C – 65C $27.95

XL-MaxSon

ar-AE 1 cm 10Hz

300in-420in

3.5V-5.5V

3.4mA - 40C – 70C $29.95

LV-MaxSon

ar-EZ 1 cm 20Hz 254in

2.5V-5.5V

2.0mA - $21.95

.

HRLV MaxSon

ar-EZ 1 mm 10Hz 195in

2.5V-5.5V

3.1mA 0C – 65C $28.95

HRXL MaxSonar-WR

1 mm 6Hz-7.5Hz

196in-393in

2.7V-5.5V

3.1mA -40C – 65C $97.95

Table 11 – Ultrasonic Proximity Sensor Comparison

64

Figure 34 – LV-MaxSonar-EZ beam Pattern Reprinted with permission

65

Figure 35 – PCB Layout of MaxSonar EZ2 Permission Pending

Figure 36 – Sensing Object within Infrared Proximity’s Detection Range Reprinted with permission

66

EZ2 is steadiest of all EZ models. It neither has the widest nor the narrowest beam width. It has a resolution of 1 inch, uses frequency of 42kHz to measure distance, virtually no dead sensor dead zone, and has maximum range of 254 inches (6.45 m). It reads from all 3 sensor outputs: analog voltage, serial and pulse width. It functions on 2mA current and voltage between 2.5-5.5V. EZ2 is a very good fit for the given specifications. Thus, from these specifications, and Figure 28 and 30, LV-MaxSonar EZ2 seems the most plausible choice for Knight Gear. The cost of EZ2 is also very reasonable with $27.95 when compared to EZ0, EZ1, EZ3 and EZ4 being $27.95, $25.95, $27.95, $27.95 respectively.

5.8.1.2 Infrared Proximity Sensor

Infrared proximity sensors send out beams of infrared light and then analyze the returning light. The photo-detector inside the sensor detects any incoming reflection of this light. These reflections allow the sensor to determine the location of the object. Infrared proximity sensor works as a triangulation as demonstrated in Figure 37. In Knight Gear, infrared light will be emitted from this sensor which will be reflected back by the person/object to the proximity sensor. The sensor will evaluate the time taken and returning angle with modulation to assay the distance. Figure 38 on the next page portrays the building blocks of infrared sensor.

Figure 37 – How infrared proximity sensor detects object Permission Pending

67

Figure 38 – Building blocks of infrared proximity sensor

Infrared sensors are relatively cheaper but are not as powerful as ultrasonic sensors. They offer short range and are not as effective outdoors as they are indoors. Bright light from the sun will affect the accuracy of infrared proximity sensor. The modulation technique provides the best chance for outdoor use however, there is an anomaly expected from the various light reflecting capabilities of surfaces in the surroundings. The list of infrared sensors that were looked up for choosing a good fit for Knight Gear are listed in table 12.

68

Products Voltage

Operational Range

Distance Price

GP2Y0A02YK0F 2.7V – 6.2V 150cm $14.95

GP3Y0A21YK 2.7V – 5.5V 10cm-80cm $13.95

GP2D12 4.5V – 5.5V 10cm-80cm $9.95

Pololu 2.7V – 5.5V 60cm $5.95

Table 12- Infrared proximity sensor comparison

The infrared proximity sensor that is being considered is Sharp‟s GP2YOAO2YKOF for Knight Gear. Sharp‟s “GP2YOAO2YKOF has an analog output that varies from 2.8V at 15cm to 0.4V at 150 cm”. It requires a supply voltage of 4.5-5.5V in DC. This sensor works best when sensing objects up to 5 feet. This should be fairly filling to the general requirements of Knight Gear because even an ideal and best proximity sensor will struggle to confront the light reflecting surfaces from the surroundings. Sharp‟s “GP2YOAO2YKOF long range costs only $14.95 when compared to Sharp‟s GP3Y0A21YK which provides short range of 80 cm (2.6 ft) and costs $13.95.

5.8.1.3 Sensor Fusion

For the betterment of Knight Gear, fusion of infrared proximity sensor and ultrasonic proximity sensor will be performed to achieve more precise, accurate, dependable and complete results. This will allow Knight Gear to follow its user in an exact and sturdy manner and the user will not have to look back or worry too much about it.

5.8.1.4 Weight Sensor

A weight sensor also needs to be implemented to fulfill the needs of this project. Knight Gear works only and only when the weight of the backpack is less than or equal to 50lbs. It will not work and will give an error signal if the weight happens to be more than 50lbs. The weight sensor works as a Wheatstone Bridge Network, where 4 strain gauges are connected with 4 separate resistors. When a force or load is applied, resistance changes and results in change in output (The voltage is zero at equilibrium with no load/force). This small change in output voltage is measured and augmented carefully from low amplitude to high

69

amplitude and then examine to calculate the weight of the load and displayed on a LCD screen to the user.

SEN-10245 load cell, shown in figure 39, will be used for the execution of weight sensor. Figure 40 shows the actual sensor that is bought from sparkfun. This sensor costs $9.95 and is not complicated to implement.

Figure 39 – Schematics of Load Cell SEN10245

Figure 40 - This is SEN10245 load cell that will be used to check the weight of the load on Knight Gear.

70

5.8.1.5 Accelerometer

An accelerometer is used in the system to detect velocity, position, shock, vibration or acceleration of gravity. It will play a major role in evaluating the localization and positioning of Knight Gear by evaluating the inertial measurement of velocity and position. Accelerometer can measure acceleration in one, two or three orthogonal axis. 2-axis accelerometer is sufficient enough for the purpose of Knight Gear and costs more than 3-axis accelerometer which provides more accurate data of x, y and z axis of Knight Gear without supplementing extra weight. Accelerometers that are looked into are listed in table. These devices and possible were looked into during the research and implementation of Knight Gear are listed below in table 13.

Products Range Interface Axes Voltage

Requirements Current

Requirements Price

ADXL 193 ±

250g Analog 1 3.5 – 6 V 1.5 – 2 mA $29.95

ADXL335 ±3g Analog 3 1.8 – 3.6 V 350µA $24.95

BMA180

±1, 1.5, 2, 3, 4,

8, 16g

SPI and I2C

3 2 – 3.6 V 650 - 975µA

This product

is retired.

LIS331 ±6, 12, 24g

SPI and I2C

3 2.16 – 3.6 V 250µA $27.95

MMA7361 ±1.5,

6g Analog 3 2.2 – 6V 400-600µA $11.95

MMA8452Q ±2, 4,

8g I2C 3 1.95 – 3.6 V 165µA $9.95

MMA7341L ±3, 11g

Analog 3 2.2 – 3.6 V - $9.95

Table 13 – Accelerometer comparison

71

Triple axis accelerometer – ADXL335, fits the best need of Knight Gear. It costs $24.95 from sparkfun when compared to double axis accelerometer – 202JE costs $20.88 from Digikey. ADXL-335 provides very low noise and uses very low power to offer sensing range of ± 3g. This sensing range of ± 3g should be very accurate in a limited range and should maximize sensitivity without losing any of Knight Gear‟s functionalities. According to ADXL-335 data sheet from sparkfun, the ADXL-335 has ratiometric output, hence “the output sensitivity varies proportionally to the supply voltage. At Vs = 3.6V, the output sensitivity is typically 360m V/g. At Vs = 2V, the output sensitivity is typically 195 m V/g.” The innovative design technique of ADXL-335 ensures very high performance and has compensated for adverse temperatures The bandwidth of ADXL-335 ranges from 0.5Hz to 1600Hz for X and Y axis and 0.5Hz to 550Hz for Z axis. It‟s small and low profile chip with dimensions of 4 mm x 4 mm x 1.45 mm and weighs only 2 grams, which makes it suitable for Knight Gear. The schematics of ADXL 335 is shown below in figure 41; and figure 42 shows the actual sensor that is bought from sparkfun.

Figure 41 - ADXL335 PCB layout Permission Pending

72

Figure 42 - This is ADXL-335 accelerometer that will be used to calculate distance, position and velocity of Knight Gear.

5.8.1.6 Gyroscope

Unfortunately, accelerometers are affected by gravity and it may not offer precise and accurate readings of Knight Gear‟s orientation, therefore gyroscope is used to enhance the performance of Knight Gear. Unlike accelerometer, gyroscope is not affected by gravity and has the upper hand when it comes to determining the orientation of an object in motion. Historically, gyroscopes were used for “space navigation, missile control, under-water guidance, and flight guidance. Now they are starting to be used alongside accelerometers for applications like motion-capture and vehicle navigation” according to sparkfun webpage on Accelerometer, Gyro and IMU Buying Guide.

In addition to gravity, vibration also affects the orientation and localization of accelerometer. As a result, dual axis gyroscope will be implemented in the Knight Gear to measure the rotation of X and Y axis and to compensate on accelerometer‟s functionality. IDG-500 Integrated dual axis gyroscope is being used for Knight Gear. It is the world‟s smallest dual axis gyro sensor with highest dynamic range to measure fast action motion. The features of IDG-500 involve two separate outputs per axis: 500 degrees/s full range for high speed and 110 degrees/s full range for high precision. Its low pass filter integration with auto zero function and a temperature sensor makes it ideal. This gyroscope has high vibration rejection over a wide range of frequency with 10,000 g of shock tolerance. Some more gyroscope products that may be suitable for Knight Gear have been listed below in table 14.

73

Products

Range Interface Axe

s

Voltage Requirement

s

Current Requirement

s Price

LPY503AL

±30/s, or ±120/s

Analog 2

(x/z) 2.7 – 3.6 V 6.8mA $29.95

L3G4200D

±250/s, ±500/s,

or ±2000/s

SPI and I2C

3 2.4 – 3.6 V 6.1mA $49.95

ITG 3200 ±2000/s I2C 3 2.1 – 3.6 V 6.5mA $49.95

L3GD20 ±250, 500,

1000/s I2C 3 2.5 – 5.5 V 7mA $24.95

LPR5150AL

±1500/s I2C 2 2.7 – 3.6 V - $29.95

IDG500 ±500/s Analog 2 2.7 – 3.3 V - $39.95

Table 14 – Gyroscope Comparison

IDG-500, schematics shown in figure 43, demands a supply voltage of 2.7V-3.3V and its output is independent of the supply voltage. It provides lowest cross axis sensitivity to accomplish the best signal accuracy and costs only $39.95 from Component distributors which fulfills more than the operational requirement of Knight Gear.

Figure 43 – PCB layout of IDG500 Permission Pending

74

5.8.1.7 Inertial Measurement Units (IMUs)

Just like how ultrasonic proximity sensor and infrared proximity sensor were amalgamated together to form a sensor fusion to ameliorate the result similarly, inertial measurement unit is created to provide 2 to 6 degrees of freedom. Gyroscope IDG-500 and Accelerometer ADXL-335 are sophisticated for Knight Gear, but individually they won‟t be able to collect readings that will result in obtaining optimum orientation, velocity and position. Hence, an inertial measurement unit is created by carefully combining IDG-500 gyroscope and ADXL-335 accelerometer. There are other IMUs that have been looked for Knight Gear. These products are listed in a table 15.

Products Range Interface Axes Voltage

Required Price

9DOF Razer Accel:±16g Gyro:360/s

Serial Accel: 3 Gyro: 3

3.3-16 VDC $124.95

9DOF Sensor stick

Accel: ±2, 4, 8, 16g Gyro:

±2000/s

I2C Accel: 3 Gyro: 3

3.3 – 16 VDC $99.95

6DOF ITG-3200/ADXL345

Accel: ±2, 4, 8, 16g Gyro:

±2000/s

I2C Accel: 3 Gyro: 3

3.3 VDC $64.95

Fusion Board ADXL345 &

IMU ITG3000

Accel: ±2, 4, 8, 16g Gyro: ± 2000s

I2C Accel: 3 Gyro: 3

3.3 – 16 VDC $59.95

MPU 6050

Accel: ±2, 4, 8, 16g

Gyro: ± 250, 500, 1000,

2000/s

I2C Accel: 3 Gyro: 3

2.3 - 3.4 VDC $39.95

Table 15 – IMU Comparison

75

5.9 Wireless Communication

In order for Knight Gear to follow a user, the group decided for a wireless communication between the robot and the transceiver. This communication could be done with a multitude of different antennas and wireless communication devices. the purpose of the implementation of wireless communication in Knight Gear is for localization of the user which is the main feature of Knight Gear and its top priority. Some wireless communications looked at were Wi-Fi, Bluetooth, and ZigBee.

5.9.1 Wi-Fi

Wi-Fi allows for LANs to be deployed without wires for different clients. Wi-Fi uses Point to hub communication, and has an operating frequency of 2.4 and 5 GHz. This method was the first one looked at when designing Knight Gear‟s wireless communication. Wi-Fi is very common in most laptops and wireless devices, and uses 802.11b or 802.11g with a range of 50-100 meters. A down side to using Wi-Fi is the complexity and knowledge needed to be able to operate them. But a positive of Wi-Fi is the range of 50-100 meters, which is very large compared to the other 2 choices.

5.9.2 Bluetooth

Another viable option for wireless communication would be Bluetooth. Bluetooth was designed for low power consumption and short range devices. Bluetooth uses radio technology to send data in chunks on different frequencies at 2.4 GHz. bluetooth has a range of 10-100 meters and is another great choice for Knight Gear‟s communication.

5.9.3 ZigBee

Lastly, ZigBee is the final choice for wireless communication in Knight Gear. ZigBee, is a low cost, low power, wireless mesh network. Devices using ZigBee operate at a radio frequency of 2.4GHz and are usually very simple devices. The communication is based on peer to peer connections and requires very little knowledge to use because of lack of complexity.

The table 16 below shows comparison on the three different wireless communication methods and different specifications.

76

ZigBee Wi-Fi Bluetooth

Range 10-100 meters 50-100 meters 10-100 meters

Operating Frequency

2.4 GHz 2.4 and 5 GHz 2.4 GHz

Complexity Low High High

Power Consumption

Low High Medium

Table 16 - Wireless communication methods

Based on these specifications, the group decided on going with ZigBee as the wireless communication of Knight Gears user following protocol.

5.9.4 XBee

When looking for wireless antennas for Knight Gear that used ZigBee, the name that repeatedly showed up was XBee by Digi. The XBee antennas are very popular with hobbyist around the world and are very low cost and easy to program and use. Even with the large amount of documentation and examples of the XBees being used, there are many different XBee models and different series of XBees to examine and decide which is best for Knight Gear. To start off, ZigBee and XBee are different things. ZigBee is the protocol while XBee is the wireless communication device. For Knight Gear, the group mainly focused on two versions of the XBees: Series 1 and Series 2.

The first is Series 1, also known as XBee 802.15.4. This model of XBees is the easiest to work with as in they require no preparation or configuration to use. They can benefit from configuration, but they do not need it. Only downside to these is that they are not compatible to XBee series 2 or above.

XBee ZB are a current version of the Series 2 of the XBee. These XBees can run in a transparent mode or work with API commands. The XBee 2B are even newer versions of the Series 2 which improve power usage. Although these two XBees are different versions of Series 2, they can work with one another unlike a Series 1 working with a Series 2.

The following table 17 shows a comparison of a Series 1 antenna with a Series 2 antenna.

77

XBee Series 1 XBee Series 2

Range 300 ft 400 ft

Power Consumption 50mA @ 3.3v 40mA @ 3.3v

Frequency 2.4 GHz 2.4GHz

Data Rate 250 kps 250 kps

Cost $22.95 $20.95

Table 17 – Xbee Series comparison

Based on the previous table showing comparisons on the Series 1 or Series 2, Knight Gear was chosen to have a Series 2 XBee RF antenna. The main reason for this choice was to alleviate the budget for the group and availability of components from SparkFun.

For Knight Gear, we will focus on serial communication using the XBee Series 2 antennas which will focus on mainly the pins 2 and 3, shown in the figure 44.

Figure 44 – Xbee Series 2 Chip

Permission Pending

78

In order to trigger the PING ultrasound sensor with the XBee Series 2, we needed to invert a serial signal from low to high using an inverter. In order to make a low cost inverter, we decided to use a PNP inverter. Using the serial out on the XBee and inverting it as shown below in the figure, we can get a high pulse trigger for the PING sensor. The PNP inverter circuit is shown below in figure 45.

Figure 45 – PNP Inverter

Permission pending

5.10 Localization

Knight Gear needs to accurately identify its position at all times regardless if it is situated outdoor or indoor. Determining where Knight Gear is, at a random point of time in extremely necessary because while navigating, it needs to avoid colliding with walls, hitting people and come to sudden stop if someone comes in front of it. There are two ways in which awareness of locality can be achieved. One way is dead reckoning system and other is using external references system. Dead reckoning system will calculate the current location of Knight Gear by using positions, fixes from past states and advances its position based upon estimated speeds, time and distance covered. This is a great technique to find Knight Gear‟s position indoor and outdoor without using any external references. However, there is a major flaw with dead reckoning system. If Knight Gear has been in motion or working for a long period of time, then incremental errors accumulate. This results in losing localization accuracy. It alone cannot be

79

precise by itself. Therefore, with the help of accelerometers and gyroscopes, dead reckoning system can prove to be more effective than before. This method will be implemented for indoor. If the user walks into the classroom building, the Global Positioning System (GPS) will not be as effective as dead reckoning system. Hence, it will be mainly used for indoor purpose. The implementation and execution of Knight Gear‟s positioning is a very convoluted problem.

5.10.1 Absolute Localization

As the name states, absolute localization locates the robot using the coordinate system. In this localization, no approximate estimation is required to initiate the localization process. This technique uses sensors to provide information on the surroundings of the robot and the information can be interpreted to determine its position based upon the coordinate landmarks. This method is relatively complex to implement and requires harnessing of the robot environment with beacons. The processing is much faster in absolute localization when compared to relative and offers data with maximum accuracy and precision. However, in absolute localization the environment has to be already set up with beacons to process the triangulation method. The purpose of Knight Gear is to follow the user outdoor and indoor locations regardless if it is a place it has been before or otherwise. Therefore, planting beacons already in the location doesn‟t fulfill Knight Gear‟s requirements. But, if something goes wrong in relative localization, absolute localization is definitely a back we can go to.

$29.99 MediaTek 3329 from Sparkfun looks like a good fit for Knight Gear. It weighs only 6 grams and provides great sensitivity at -165dBmW. The schematics of MT3329 GPS module is shown below in figure 46.

Figure 46 - EM406 connector for the MT3329 GPS module Permission Pending

80

5.10.2 Relative Localization

This technique is the same as dead reckoning system. Current position of the robot can be determined incrementally by evaluating displacement, initial positioning, speed the robot is travelling, and direction it is travelling. Sensors like gyroscope, accelerometer, and inertial measurement units help in calculating the relative localization of the robot. This method gives advantage to the position of the root with an elevated frequency. However, this technique incorporates a lot of minute errors that add up. These errors are wheel slippage, uneven floors, and lot of incremental errors that accumulate to give localization with accumulated errors. Local positioning system is chosen instead of a global positioning system because the global positioning system introduces the need for a global observer into the team. Many of the currently available global positioning systems are not accurate enough for Knight Gear. Satellite based GPS is accurate up to within a couple of meters. Satellite based GPS also works very poorly when indoors or in enclosed areas. Instead, a local positioning system was used to maintain the formation parameters in the robot team. The position of relative localization is shown below in figure 47.

Figure 47 – Relative Localization Permission Pending

From the figure above, the following equations can be concluded:

xK+1 = xK + ΔDK . Cos (k +Δk/2)

yK+1 = yK + ΔDK . Sin (k +Δ

k+1 = k +Δk

In order to localize Knight Gear accurately, it is important to minimize the number of incremental errors. Therefore, several motor schemas, static obstacle, move to

81

goal, and maintain-formation are implemented. These additional algorithms will not affect the overall orientation and configuration of Knight Gear. Furthermore, background schemas and noise form a reactive grease, which deals with some of the problems that is based entirely on navigational methods. Each of these schemas engenders a vector that represents the desired behavioral response which is stimulated by current sensory. Simultaneously, the importance of these individual behaviors is demonstrated by a gain value. Multiplication of the outputs of these individual behaviors by its gain, and then summing and normalizing the results provides a high level combined behavior. The maintain-formation motor schema causes a movement vector towards the desired formation position. The direction of the vector is always towards the desired formation position however, the magnitude relies on how near or far the robot is away from it. Using the distance from desired position, three zones are basically used for magnitude computations. The radii of these zones are the guidelines to maintain formation schema. According to a weekly report on cooperative control project, the magnitude of the vector is calculated as follows:

“Ballistic zone: the magnitude is set at its maximum, which assimilates to the schema's gain value.”

“Controlled zone: the magnitude varies linearly from a maximum at the farthest edge of the zone to zero at the inner edge.”

“Dead zone: in the dead zone vector magnitude is always zero. The role of the dead zone is to minimize the problems associated with position reporting errors and untimely communication.”

To ease the discussion that follows, the following formation terms are introduced:

Rpos, Rdir the robot's present position and heading.

Rmag, the robot's present speed.

Fpos, the robot's proper position in formation.

Fdir, the direction of the formation's movement; towards the next navigational waypoint.

Faxis, the formation's axis, a ray passing through Fpos in the Fdir direction.

Hdesired, desired heading, a computed heading that will move the robot into formation.

heading, the computed heading correction.

speed, the computed speed correction.

Vsteer, steer vote, representing the directional output of the motor behavior, sent to the steering arbiter.

Vspeed, speed of the motor behavior, sent to the speed arbiter. The magnitude of the required speed correction is determined and evaluated by the maintain formation speed behavior, and then it casts its vote by adding the correction to the current speed to minimize the accumulated errors.

Vspeed = Rmag + K speed

82

In the above equation,

K is a constant that is set before the actual runtime in order to adjust the rate of correction.

speed is the correction calculated by formation speed behavior.

The three zones: ballistic zone, controlled zone, and dead zone determine speed. The sizes of these zones are the parameters of formation behavior.

speed is set negative if Fpos of the robot is negative. speed is positive if Fpos

of the robot is positive.

In a method very similar to the motor schema-based approach the magnitude is computed as follows according to weekly report on cooperative control project:

Ballistic zone: 1.0

“Controlled zone: the magnitude varies linearly from a maximum of 1.0 at the farthest edge of the zone.”

“Dead zone: in the dead zone the magnitude is always zero.”

The maintain-formation-steer behavior follows a similar sequence of steps to evaluate an egocentric steering direction, the angle for the front wheels with respect to the vehicle body. The magnitude of correction is necessary to calculate using this behavior. The magnitude of correction is determined based on how far laterally the robot is from its formation position. The maximum correction is for the robot to head directly towards the formation axis, the minimum is for the robot to head directly along the formation axis. The magnitude of heading computed by the formation heading behavior is determined as follows

Ballistic zone: 90, i.e. head directly towards the axis.

Controlled zone: the turn varies linearly from a maximum of 90 at the

farthest edge of the zone to 0 at the inner edge.

Dead zone: 0, i.e. head parallel to the axis.

The sign convention of the correction is set according whether the robot is left or right of the formation axis. The sign is positive if the robot is on the left side of the axis and is calling for a right turn. The sign is negative if the robot is on the right side of the axs and is calling for a left turn. Hdesired can now be determined with reference to the formation axis:

Hdesired = Fdir - heading

The heading will bring it to formation axis and align it properly when Knight Gear continues moving. On the other hand, if the formation has stopped moving then, Hdesired is instead set to take the robot directly to its position:

83

Hdesired = Fpos - Rpos

Ultimately, Hdesired is translated into an egocentric angle for Knight Gear‟s front wheels:

Vsteer = Hdesired - Rdir

The positive angle designates a right turn and negative angle designates a left

turn. If the result of the angle is either greater than 180 or less than -180, 360 is added or subtracted to ensure the result is within bounds. Finally the angle is clipped to the physical limits of the vehicle.

Knight Gear‟s positioning can be seen as determining the relative distance between the user and Knight Gear. Considering the range in which Knight Gear will be active and the accuracy needed, another method can be used for the localization. A trilateration system will be used to fulfill desired requirements. This system is based on the time taken for an ultrasonic signal to traverse a certain distance. The distance between two points can be measured using the time taken for an ultrasonic signal to travel from one point to another in an open space. By emitting an RF signal and Ultrasonic signal simultaneously the difference of the time for the two separate signals to reach a certain target can be considered as the time for the ultrasonic signal to travel between the two points since the speed of a RF signal is much faster than the speed of an ultrasonic signal. This, however, will only be sufficient to calculate the distance, not an actual position. Using this distance a parameter can be drawn around the receiving point and the signal would have originated somewhere on the perimeter of this circle. If there are two more receiving points also measuring the time difference between the RF signal and the ultrasonic signal two more circles can be drawn around those points and the point at which all of these circles intersect will be the point where the signals emitted. This idea was used to create a local positioning system on Knight Gear. By locating three receiving points on advantageous positions on a robot‟s local coordinate system, namely A, B and C, the required equations can be derived to estimate one robots position with respect to another. Figure 48, displays a graph with A,B and C coordinates.

84

Figure 48 –Relative coordinate system for Localization Permission Pending

( )

( )

( )

( )

( )

( )

Let

By substituting we get,

( ) (1)

( ) (2)

( ) (3)

( ) ( )

85

(

)

( ) ( )

(

) (

)

(

) (

)

The relative angular position is also an important factor in determining Knight Gear‟s positioning. Most applications have either used compasses or GPS modules in order to determine the relative angular positions. Having said that, the relative angular position can be determined by using 3 ultrasonic beacons instead of 1 with each beacon being on the origin, X-axis and Y-axis of a robot frame, respectively. The approach mentioned does not require the use of additional types of sensors other than the ultrasonic sensors already being used. The drawback of this method is the requirement of multiple capture modules in order to measure the distance to 3 beacons except of 1.

Considering that the Knight Gear doesn‟t require sharp angular movements the error that can be accumulated can be considered negligible. Once the relative position and orientation between the members of the robot team are determined, the instantaneous angular and linear velocities can be determined by speeds of the wheels on the differentially driven robots as shown in figure 49.

𝒙 (𝒅𝑩 𝒅𝑪)(𝒅𝑩 𝒅𝑪)

𝟒𝒅

𝒚 (𝒅𝑩 𝒅𝑨)(𝒅𝑩 𝒅𝑨) (𝒅𝑪 𝒅𝑨)(𝒅𝑪 𝒅𝑨)

𝟒𝒅

86

Figure 49 – Determination of instantaneous angular and linear velocities Permission Pending

A complete understanding of the dynamic state of the formation of the team of robots can be obtained by measuring the relative distances, relative angular positions with the use of ultrasonic sensors and the linear and rotational speeds of each robot through feedback from the driving motors. The parameters needed to maintain the formation can be shared by communication between the master and the slaves using RF communication according to a specific. This is another advantage of using RF signals for the trilateration system

In order to obtain the required positions, orientations and speeds after making the necessary data acquisitions a feedback control system was necessary. The most attractive choice was a PID control system because it is a suitable, tested and proven control algorithm for the controlling of mobile robots. Two separate PID control loops were needed in order for obtaining the required linear/angular velocities from the required positions/orientations and the ultrasonic sensory data inputs and subsequently to obtain these required velocities through controlling the rotational speeds of the driving motors through PWM signals and encoder feedbacks. The block diagram of the controller is shown on next page in figure 50.

87

Figure 50 - Controller Block Diagram

5.11 Control Algorithm For controlling Knight Gear, we decided on using a proportional-integral-derivative controller (PID Controller) to have it follow the user. In addition to this we add collision detection algorithms to avoid obstacles as Knight Gear makes its way towards the user. Additionally we use Bluetooth and GPS as additional input signals for the PID controller. The PID controller calculates the current error, the integral of the previous errors, and divertive of the future errors to calculate the ideal turning angle to stay on target. All three types of errors are multiplied by a coefficient and then added together. The value of these coefficients dictate if and by how much the target will be overshoot by the correction angle calculated by the PID controller. The effects of the integral coefficient can be seen in the figure below, figure 51.

88

Figure 51 – Effect of the integral coefficient Work in public domain.

As can be seen in figure 37, a high integral coefficient causes a huge initial overshoot of the target and big ripples in accuracy, thus a low integral coefficient would be used in Knight Gear‟s PID controller. The effects of the current or proportional error coefficient can be seen in the figure below, figure 52.

89

Figure 52 – Effect of the Proportional coefficient Work in public domain.

Figure 38 shows that a high proportional error coefficient can also cause a large overshoot, thus a small value would be chosen. The value of the proportional error coefficient must however be great than the value of the integral coefficient since we want the proportional error to be the major driving force of the PID controller. The effects of the derivative coefficient can be seen in the following figure, figure 53.

90

Figure 53 – Effect of the Derivative coefficient Work in public domain.

As can be seen the change in the derivative coefficient does not change the magnitude of the overshoot by much, but it does affect the length of time the overshoot is in effect. As the coefficient rises however, the ripple‟s magnitude decreases, thus one would like a higher derivative coefficient, but not one that is greater than the proportional coefficient. The main control algorithm will call the PID controller with the sensory information from the infrared and ultrasonic fused sensors. The PID controller will use the previous values to calculate the error, integral, and the derivative and return to the main control algorithm two velocities which will be passed to the front motors causing Knight Gear to turn on the direction of the slower front motor. These velocities are calculated with adding to the left front motor and subtracting from the right front motor the PID‟s error correcting velocities to a base velocity used for all four motors. This is done since a positive correcting indicates that the user is to the right of Knight Gear and it needs to turn so by increasing the motors of the left front wheel, while a negative value indicates that the right front wheels must speed up to turn leftward. Before the velocities are sent to the motors the main control algorithm will call the collision detection algorithm with the ultrasonic information from the ultrasonic sensor and Knight Gear‟s planned motion vector to determine if there is an object in front of Knight Gear and if it will collide with it. If there is no imminent collision

91

the collision detection algorithm does not alter the velocities of the motors; however, if there is an imminent collision the algorithm then decides if it can be avoided by moving an arc or to stop Knight Gear completely. This is determined by using the relative localization calculations to determine if the object will come into collision because it is headed to Knight Gear, if Knight Gear is headed towards the object, or if the vectors of Knight Gear and the object would intersect soon. From there it the algorithm calculates the most efficient method of avoiding the collision; for example, if Knight Gear is in a collision course with a moving obstacle it would most likely be best to just stop advancing until the obstacle has passed the vector of movement. If there is no IR signal to supply the PID controller the main control algorithm will instead use GPS or Bluetooth signals depending on which gives the more accurate reading. Bluetooth will be implemented due to the lack of accurate GPS signals while indoors. Using these signals Knight Gear would continue to use the previous values calculated in the PID controller to locate the user and continue to follow them with the infrared and ultrasonic fused signals. The class diagram is shown below in figure 54.

Figure 54 - Class Diagram for the Control Algorithm

92

5.12 Microcontrollers

For the project of Knight Gear, the group decided that a good choice would be to have one central microcontroller for all the heavy computing and multiple small controllers for sensors, motors, and accessories. The central microcontroller does not need to be very powerful, but enough to be able to handle and process all incoming data that is simplified by the smaller, weaker, outer microcontrollers which handle the analog I/O from the devices. First, microcontrollers must be examined for the central unit. This controller is the most vital, as it is the main processing unit for the tracing algorithm which decides all the other functions of the Knight Gear robot. Later, smaller controllers will be examined in order to decide on motor controller, sensor controller, and accessories control (such as GPS, Bluetooth, etc.).

5.12.1 MC68332

The Motorola MC68332 is a viable option for the project Knight Gear. The MC68332 processor comes with a Linux operating system and is programmable in C and C++. It can be programmed in C and is very low cost of $11.94, so it has become a good choice for the project. These microcontrollers are very versatile because of the many I/O ports on it. The processor also is very small, and can be easily placed in the chassis of Knight Gear. Since the MC68332 is a 32-bit microcontroller, and has 2-Kbyte static RAM, it can be a very good fit as a central processing unit for the whole system for interpreting all the signals from the motor controllers and sensor controllers.

5.12.2 PIC 18F452

The PIC18 Family of microcontrollers is another option for the project Knight Gear. This processor is a RISC processor, has 16-bit instructions, and is programmable in C. These processors also have 28 pins, making them another great choice for the central processor of Knight Gear. Looking specifically at the PIC 18F452 processor, at a cost of $4.68 it is cost effective and useful for the project Knight Gear. If this processor is used as the central processor, the group would be trading cost over memory.

5.12.3 Intel 8051

Lastly, the Intel family of microcontrollers has a processor small and powerful enough to match the specifications needed for the microcontroller, and that is the Intel 8051. The 8051 is an 8-bit microcontroller, has 32 input/output lines, and is programmable in C using Keil IDE embedded development tool. It‟s small power usage and low memory is perfect for taking input and outputs from the sensor systems or the motor systems.

93

5.12.4 Atmel ATMega2560

Another great option for the microcontroller for Knight Gear is the Atmega 2560

from the Atmel family. Specifically speaking, the Mega Pro 3.3v from Sparkfun.

This microcontroller allows for Knight Gear to fully use all the pulse wave

modulation lines that it requires for all of the ultrasound sensors and for the motor

drivers. With a 3.3 volt operating voltage, 54 digital I/O pins, 15 of them being

PWM, 16 analog inputs, and a large amount of documentation from different

hobby websites make the Mega Pro a great low power option for the

microcontroller for Knight Gear.

5.12.5 Microcontroller comparison

In all, the four microcontrollers could be implemented in different ways to make

the robot, Knight Gear, function properly. The table 18 below shows how the

microcontrollers compare to one another in order to choose a viable option.

MC68332 Intel 8051 PIC 18F452 Atmega 2560

Digital I/O 15 24 24 54

Analog I/O 15 8 8 16

Operating Voltage

5V 3.3V 5.5V 3.3V

Cost $11.94 $1.50 $4.68 $17.98

Table 18 - Comparison of the three microcontrollers

Based on the table, and on what the group and the project require form the microcontroller, the best choice would be the Atmega 2560 from Atmel. Shown below in figure 55 is the schematic diagram for the Mega Pro 3.3V from Sparkfun, which is what the group will be using when working with Knight Gear.

94

Figure 55 – Schematic diagram for the Mega Pro 3.3V Permission Pending

Below is the pin connection for the Mega Pro 3.3V in figure 56.

95

Figure 56 – Pi Connections of the Mega Pro 3.3V Permission Pending

The following figure 57 represents the power schematic of the ATMega2560.

96

Figure 57 – The Power Schematics for ATMega2560

5.13 Budget and Financing

For the senior design project Knight Gear, the expenses will be covered mostly by the group members. The group will pay out-of-pocket for all cost related to the parts acquisition, labor, and building of Knight Gear. As a group, each member will put in between $50 - $100, depending on how much all the parts in total will cost. As of now, the group has no outer funding or support so the cost of Knight Gear is being kept near $200 unless the parts and labor overshoot that limit. $200 dollars is the soft cap for the financing of the whole project.

If the expected cost for Knight Gear surpasses $200, the group will in turn look for support for funding the extra costs of the project. Parts will start being acquired as quickly as possible to ensure that the prototyping and testing is done quickly and efficiently. One of the decisions made by the group was to acquire and test parts quickly in order to get replacements in case of malfunctions or miscalculations of parts chosen. A table of the cost of parts is shown below.

97

5.13.1 Finance Table

Our estimated finance that will go in the implementation of Knight Gear is listed below in Table 19.

Part Cost

Ultrasound Sensor $27.95

Infrared Sensor $13.95

Weight Sensor $9.95

Accelerometer $24.95

Gyroscope $39.95

Battery $5

Motor $12

Motor Controller $1.87

Chassis $27.30

Microcontroller $4.68

GPS Module $29.99

Camera System(Optional) $39.99

Total $237.58

Table 19 – Finance Table

98

5.13.2 Man Hour Costs

The work put into Knight Gear by the group has no monetary cost, but does have time spent. During research and designing of the robot alone, the group has spent over 10+ hours each member. When added to an estimate of 20 hour each member for prototyping and testing, that would give a total of 30+ hours per member spent on the project Knight Gear.

99

6. Design Summary Knight Gear is an autonomous robot with the purpose of following a single user for the purpose of assisting them with carrying their materials around. The robot has multiple systems being implemented at once, and some of these communicate with one another. The major systems are Power, Motors, Sensors, and Central Processing. In this section, these four systems will be defined and their functionality explained. Also in this section, how all four of these systems work together will be explained.

6.1 Power System

The power system for Knight Gear is very intricate. Knight Gear will have a NiMH as the main power source. This was chosen because of the high capacity it has. It has a total of 9.6 V with 2100 mA, and is a very good power source for Knight Gear. This is the main part of the power system for Knight Gear. Another major component of the power system for Knight Gear is the solar panel that is being implemented into it. One of our goals with the power system for Knight Gear was to make the battery rechargeable, while it is in standby, with a solar panel. This feature adds to the survivability of Knight Gear as it operates during the day and outside. Lastly, Knight Gear has 3 different voltage regulators that will be implemented in order to power the motors, sensors, and microcontroller. These voltage regulators vary between 9V, 6V, and 3V. These components all together define the power system of Knight Gear, and a block diagram of this has been shown in the group‟s power research and implementation section.

The power on Knight Gear will be either on or off. When the robot is off, the solar panel will be charging the battery, if possible. This will give the battery more lifetime and in turn give Knight Gear a longer operating time. When the power is on, the solar panel will switch off and the battery will power the components of Knight Gear. While power is activated, Knight Gear will run until one of two scenarios happens. One being that power will be used until standby mode or turned off. The way Knight Gear will be used, this seems like the most common case because the user would only need to carry a load for short bursts of time. This gives Knight Gear a very long battery life when though about because a person has the chance to stop and set Knight Gear into standby or will reach their destination in a short amount of time. The second scenario is that power will be used until the battery has no more charge. This would be a very unlikely case because of who the intended user is. The user wouldn‟t be using Knight Gear for extremely long periods of time. Shown below is the discharge rate for the 9.6 V NiMH battery that is being implemented in Knight Gear. As the graph shows, the discharge time is very long and shows how the battery, if used how it is designed to be used in short periods of time, will give Knight Gear a very long life. The discharge cure is shown in figure 58 on next page.

100

Figure 58 - Discharge curve for 9.6V NiMH battery Permission Pending

6.2 Control System

The control systems of Knight Gear can be divided into several components such as formation controlling level, communication level, and individual decision making. Robot controller can have a multi-level hierarchical architecture such can be distinguished as artificial intelligence level, control mode level. It is important to address the all the levels in order to achieve good results.

The simplest case the control system of a mobile robot consists of at least input module (sensors), control module and output/driver module (motors). A block diagram of such control system is shown below in figure 59.

Figure 59 - Block Diagram of Navigated Control System

Permission Pending

101

6.3 Motor System

Now that the power system for Knight Gear has been defined, the motor system is very simple to define. The motor system for Knight Gear consists of four 6V DC spur gear motors and a Texas Instruments SN754410 motor controller. The motor system will be directly affected by the power system and the central processing system. The four 6V DC spur gear motors will be powered by the power system using a 6V voltage regulator. These four motors will have to move one individual wheel each, because we are looking to carry loads and if one motor had to power multiple wheels the weight of the load Knight Gear would have to carry would decrease. In the design of Knight Gear, there will be two extra wheels that will not be powered by the motors and will only be implemented for stability reasons. The motor controller from the motor system will be directly communicating with the central processing system. The central processing system will be telling the motor controller whether it needs to slow down, speed up, turn left, or turn right. All of these commands will come from the microcontroller in the central processing system, which will be computing multiple factors from the sensor system. Out of the four main systems that make up Knight Gear, the motor system is the simplest of them.

6.4 Sensor System

The third main system in Knight Gear, and one of the most important ones, is the sensor system. The sensor system is composed of ultrasonic proximity sensors, infrared proximity sensors, weight sensor, accelerometer, and gyroscope. Starting with the ultrasonic sensors, specifically the LV-Max Sonar EZ2, Knight Gear will use these sensors for two purposes. First being the locating of the user. This will be done by using multiple ultrasound sensors on Knight Gear picking up on an ultrasonic signal being sent from the user. With multiple ultrasonic sensors, Knight Gear can use the data received as distances from each sensor as a way to calculate which direction the user is. The second function of the ultrasonic sensors is collision avoidance. This is a very important function of Knight Gear. The tracking algorithm would be in the central processing system. So all the ultrasonic sensors are doing is sending data directly to the microcontroller which in turn will take the data and analyze where the user is. Knight Gear also implements an infrared proximity sensor, the Sharp‟s GP2YOAO2YKOF. This sensor is being implemented to increase the accuracy of Knight Gear‟s tracking capabilities. The infrared sensor will lock on to the user and keep track of which way he turns, making it easier for Knight Gear to follow at a close distance. With both ultrasound and infrared sensors, Knight Gear‟s tracking capabilities will be much easier to implement because of the redundancy that it would have. This extra redundancy is useful because if there are other signals in the area that are the same that Knight Gear uses, we at least have a backup in case one of the sensors gets distorted by the outside. Another sensor that is part of the sensor system is the weight sensor. The weight sensor, the SEN-10245 load cell, serves a specific purpose. One of the major goals of Knight Gear was to be able to carry

102

up to 50 pounds, and if it exceeds the weight limit, Knight Gear would shut off. This sensor lets the group implement this goal for Knight Gear. The weight sensor would sense the load of Knight Gear and let the microcontroller know this weight. Next sensor that is part of the sensor system is the accelerometer. The accelerometer being used is the ADXL335. This accelerometer is being used for measuring the inertial measurements of Knight Gear in order to help in braking, speed up, and slow down of the motors that move Knight Gear to different positions. By sensing the velocity of Knight Gear with the accelerometer, the central processing system can calculate how to implement better tracing and movement. Last sensor that is part of the sensor system is the gyroscope. The Gyroscope being used by Knight Gear will be the IDG-500. The choice of including a gyroscope into Knight Gear was one that came up when talking about how gravity can affect an accelerometer. By including this gyroscope into Knight Gear, all of the reading from the accelerometer will be much more accurate because of said gyroscope. Accuracy and redundancy were the main concern when talking about how Knight Gear would implement its sensor system.

6.5 Central Processing System

The last main system of Knight Gear is the Central Processing system. This system includes the microcontroller. This system is what makes Knight Gear do everything. All other systems rely on this central processing system. The microcontroller is the PIC 18F452 by Microchip. This microcontroller was chosen for Knight Gear because of its programmable memory size and low cost. This microcontroller will house the tracking algorithm, the collision detection and avoidance algorithm, and will keep track of the state of Knight Gear. The state of Knight Gear will either be “standby” or “work”. Standby state will happen whenever Knight Gear senses the user is not moving for longer than sixty seconds. This will be a timer kept in the microcontroller and once it activates the standby status, the microcontroller will let the power system know that it can switch to let the solar panel charge the batteries. The microcontroller does not stop its functions for tracking and tracing movement though. It will continue to tell the sensors to check if the user is moving or not. Once Knight Gear sense movement again, it will let the power system know sot switch back from solar panel charging to battery use. For the tracking algorithms, Knight Gear will sense if the user is moving left or right and also check if the user is moving forward or backwards. This will be done by the microcontroller telling the sensor system to check where the signal is and take back timing data which can be converted to distance inside the microcontroller. Once the distance from Knight Gear is calculated, the central processing system will signal the motor controller with speeds for each of the four motors. These speeds that it signals out, determined by the tracking algorithm, will in turn make Knight Gear move towards the user signal. This process of looking for a signal and commanding the motor controller will be repeated many times at a high speed, making it so that Knight Gear never loses where the user is.

103

6.6 Code Flow The figure displayed below defines our robot at simplest level. This code flow shown in figure 60, is the basis of our software design. Knight Gear pings the user and the user emits ultrasonic waves to Knight Gear. It detects and wave and direction vector is calculated after minimizing any noise, if there is. Sensors emit ultrasonic waves for collision detection. If sensors do not time out and the calculated distance is less than 0.5m, then collision avoidance vector is calculated and knight gear advances to the new calculated vector. If sensors do time out then Knight Gear advances on the new calculated direction vector.

Figure 60 - Code Flow of Knight Gear

104

7.1 Description of Prototype

We implement a virtual prototype of all subsystems of Knight Gear on Xilinx. We will use this to prototype the response of the sensors. Using Xilinx we can see what data the sensors would return depending on the input data we provide and we can learn what to expect when we build the actual robot.

7.1.1 Prototype Design

Using Xilinx we will build Verilog or schematics for each sensor and the motors. We then test the inputs required by the motors to spin to their appropriate angular velocities and we test the link between the sensors and the motors. After doing these tests of concepts, the components of Knight Gear and the user‟s transmitter should be tested before being integrated into the prototype. Finally after that, the prototype can be build and the software that allows Knight Gear to follow the user is tested.

7.2 Components List

These are the components that will be used in the implementation and execution of Knight Gear. This is a tentative components list; number of a particular device may or may not change depending on the functionality of each device in this list below in table 20.

105

Components List

3 Ultrasonic Sensors

1 Four-Wheel robot frame

1 Infrared Sensor

1 Infrared Tag

4 Wheel Motors

1 Solar Panel

1 Solar panel battery recharger

1 Chassis

1 Weight Sensor

1 IMU

1 GPS Module

1 Camera System

2 Motors

2 Xbee Antennas

Table 20 – Components List

7.3 Prototype Construction

The prototype for Knight Gear will be built to test out all the basic functions of Knight Gear as defined previously. The main prototype is built after finishing the tests on Xilinx and fully testing the sensors themselves to verify that they are in working condition. The sensors are attached to the Knight Gear prototype along with downloading the main control software. The four wheels are attached to the four individual motors with are connected to the main controller which assign them there angular velocities. After attaching the wheels and the carry case the solar panel is attached to the battery. With the psychical prototype finished the transmitter is built. The transmitter will have a clip that attaches it to the user‟s belt and will contain one ultrasonic sensor and an infrared tag. The tag is used to locate the transmitter and the ultrasonic sensor is used to increase the accuracy of the ultrasonic sensor on the prototype.

106

7.3.1 Frame Assembly

The frame will be bought premade, but will not contain the carrying case, wheels, or CPU. This is was decided as a time saving measure as building a robot frame from scratch would take too much time especially since only one member of the group is familiar with building similar machines. We will attach the motherboard to the frame and connect the four motors to both the frame and the motherboard. The power supply will be connected both to the mother board and to the solar panels which will be used to recharge the batteries while the prototype is in use outdoors. On top of the frame we will add one container 24 inches tall to the frame and strap the solar panels on top of its lid.

7.3.2 Steering System

The prototype will implement the main controller that scans for the user using both the infrared and ultrasonic sensors and then sends that information in the PID controller. The infrared sensor is used to determine the location of the user, while the ultrasound sensors are used to determine the distance from the robot. The sensors are rotated until the user is located by the infrared sensor, then the ultrasound sensors are pulsed so to triangulate the distance from the user with how long it took for the echoes to return to Knight Gear. The data is given to the controller which then calculates how off center Knight Gear is from the user; this is known as the current error value. With this the controller then calculates a velocity vector using this error along with the previous error values and potential future error values to reach the user. The vector formula uses three constants, one for each of the three types of errors, as multiplier to determine how much of an impact the specific errors have on the velocity vector of the robot. Then the collision avoidance controller takes the vector and uses the ultrasound sensors to verify that the robot is not headed for a collision. If it detects no imminent collision the velocity vector is forwarded to the motor controllers motors. If there is a collision, the controller would calculate a new vector to avoid the collision dependent on where the collision is from. If the collision is not straight in front of the robot, the robot makes a new vector that allows the robot to advance and still avoid the collision. If the collision is directly in front of Knight Gear, then Knight Gear will stop and wait a while to see if the object in front of it moves or not, then either continue or advance to its left if possible. The velocity vector that Knight Gear will implement is send to the motor controllers that decode the vector into the velocity at which the individual motors must spin at for Knight Gear to advance in the instructed vector. The graphical representation is shown in figure 61 on next page.

107

Figure 61 - Flow chart for the prototype software.

7.3.3 Sensors

After finishing the proof of concept, the transmitter and the robot can start being built. The transmitter will have a ultrasonic transmitter embedded in it to improve the ability of the software in Knight Gear to locate and follow the user and will have an infrared tag used for the infrared sensor to pick up. These are tested before being implemented into the robot verifying their data with those of the Xilinx prototype. The infrared tag should be picked up by the infrared sensor and the two ultrasonic sensors should be more accurate than just using the ultrasonic sensor on the machine.

108

8 Testing 8.1 Safety Harness

To ensure if Knight Gear is safe for public location, lot of testing will be done indoors and outdoors. Does, Knight Gear possess any threat to people in the surrounding? This is a prime question that needs to be checked after the prototype is built. Knight Gear should be very well harnessed to keep it within its limits. It is not specifically decided that how this segment of Knight Gear will be test, however it is reasonable to implement a force sensor if necessary.

8.2 Dimensions

To test the dimension, we go back to the goals and specifications of Knight Gear. Dimensions will be marked on the floor and the building of the framework will be carried out meticulously throughout the project. This will give very less percent error to the desired dimensions of Knight Gear.

8.3 Sound Level

During the testing of Knight Gear, there is also a segment that determines if the sound level is too loud to disturb the people around. For this type of testing, we would need volunteers‟ feedback if they think the noise level is too much or not.

8.4 System Tests The following sections are used to test the functions of Knight Gear, along with its components. Included are tests for the infrared, ultrasonic, and weight sensors and the motors. There are also tests for Knight Gear‟s ability to follow the user while they do simple, complex, and specific actions and areas. These tests will be used to edit the parameters of Knight Gear if need arises. All tests will be conducted inside the University of Central Florida inside or in the vicinity of the Harris Corporation Engineering Center and the Engineering I building.

8.4.1 Infrared and Ultrasonic Sensor Tests The transmitter for Knight Gear‟s user is attached to the user‟s back and should be unobstructed, preferably clipped to the belt of the user. These tests are designed to ensure the transmitter emits the proper tags so that the robot can follow the user properly. The tests should be concluded in a lab were the signals transmitted by the sensors can be measured. The tests are listed on the next page in table 21.

109

Test Description Outcome Comments

The tester should have the infrared sensor emit a beam that should be deflected on the transmitter. The transmitter should be no more than 30 cm from the sensor. The sensor should return the distance of the transmitter.

The tester should have the transmitter within one meter of the ultrasonic sensor. The sensor should detect and return the distance from the transmitter to the sensor.

The tester should have both sensors on at the same time and have the transmitter be equidistant from both while being within reach of both (30 cm). Both sensors should give the same distance from the transmitter.

Table 21 – Infrared and ultrasonic sensor tests

8.4.2 Simple Movement Tests

These tests are made to test simple movements of the robot, such as following the user in a forward line, turning left to follow the user, or turning right to follow the user while the user is in sight of the robot. One more test should be conducted to make sure the robot would rotate to locate the user then advance toward the user. These tests should be conducted in an open area, with two testers. One tester should take the role of the user while the second tester should turn on the robot when the user is in position. The testing is listed on the next page in table 22.

110

Test Description Outcome Comments

The user should stand about five meters in front of the robot. The other tester should then turn on the robot. The robot should now search for the user and after locating it in front of it, it will move straight forward. The robot should stop about half a meter away from the user.

The user should stand about five meters in front of the robot and one meter to the right of it. The other tester should then turn on the robot. The robot should locate the user and gentle curve forwards and to the right and stop within half a meter from the user.

The user should stand about five meters in front of the robot and one meter to the left of it. The other tester should then turn on the robot. The robot should locate the user and gentle curve forwards and to the left and stop within half a meter from the user.

The user should stand five meters to the right of the robot. The other tester should then on the robot. The robot then would scan for the user, turning counterclockwise until it locates the user. The robot should then head towards the user and stop within five meters from the user.

Table 22 – Simple movements tests

8.4.3 Simple Following Tests

These tests are meant to test the ability of the robot to follow the user in simple paths without obstacles. These tests require only one tester who will act as the user. The tests should be conducted in an open area. The testing is listed below in table 23.

111

Test Description Outcome Comments

The user should turn on the robot. Then walk forward for fifteen to twenty meters in a straight line. The robot should follow in a straight line and stop within half a meter.

The user should turn on the robot. Then walk in a curved path to their right for fifteen to twenty meters. The robot should follow in a smooth arc behind the user and stop within half a meter.

The user should turn on the robot. Then walk in a curved path to their left for fifteen to twenty meters. The robot should follow in a smooth arc behind the user and stop within half a meter.

The user should turn on the robot. Then walk forward for five meters, then turn left and advance ten meters, and finally turn right and advance forward. The robot should follow and make smooth curves whenever the user takes a turn and stop within half a meter from the user.

The user should turn on the robot. Then walk forward for five meters, and then stop. The user should wait for the robot to catch up, then continue walking forward another five meters, then stop again and wait for the robot. The user then waits for the robot to come to a complete stop before advancing ten more meters. The robot should follow and stop within half a meter from the user, and continue to follow when the user starts walking again.

Table 23 – Simple following tests

8.4.4 Basic Obstacle Avoidance Tests

These tests are designed to test how the robot handles basic obstacles such as hills, corners, and bystanders. The hill test can be tested in front of the Harris Corporation Building in the University of Central Florida. The other tests may be conducted indoors or around buildings. The hill test and the corner test only require one tester to act as the user, while the bystander test requires two testers: one to play the user and one to play the bystander. The testing description is listed on next page in table 24.

112

Test Description Outcome Comments

The user should turn on the robot. Then the user should walk straight up and down a hill or pair of inclined planes. The robot should move straight up the hill then down the hill without stopping.

The user should turn on the robot. Then the user should walk towards a corner either indoors or around a building. The robot should follow the user around the corner, avoiding collision with the corner and not stopping.

The user should turn on the robot, while the bystander is five meters in front of the robot. The user should walk towards the bystander and go around them. The robot should follow the user and avoid the bystander. The robot should not stop while avoiding the bystander.

Table 24 – Basic obstacle avoidance tests

8.4.5 Advance Maneuvering Tests

These tests are designed to gauge the maneuverability of the robot by seeing how adaptable it is to rapid movements of the user. This is represented by the user moving faster or slowing down and having the robot adjust its speed to match the user‟s speed. Another test would have the user change directions sharply and quickly having the robot follow the user. A final test would make sure the robot can avoid incoming obstacles such as walking bystanders. The first two tests need to be done in an open area or hallways were sharp turns are possible. The final test requires multiple testers to take the role of bystanders to impede the robot and force it to avoid them while following the user. The testing of advance maneuvering is listed on next page in table 25.

113

Test Description Outcome Comments

The user should turn on the robot. Then they should start walking forward for ten meters. Then the user should increase their speed and move for another ten meters. Finally they should slow down back to walking speed. The robot should be following the user and be matching their speed. Thus the robot should slow down when the user slows down.

The user should turn on the robot. Then the user should walk forward and take sharp turns quickly. The robot should follow the user, it might stop on the turns to look for the user, but it should only occur when the user takes an incredibly sharp turn really quickly.

The user should turn on the robot. Then the user should move forward for then meters, then do a U-turn and walk fifteen meters. Afterwards a sharper U-turn should be taken. The robot should follow the user without stopping on the first U-turn, but it might for the second turn.

The user should turn on the robot. Then they should walk towards the bystanders. The bystanders then slip in between the user and the robot. The robot should sense the bystanders and avoid them, and then it should look for the user and try to catch up if needed. The robot should not stop when avoiding the moving bystanders, but it might stop when looking for the user.

Table 25 – Advanced maneuvering tests

8.4.6 Indoor Performance Tests

These tests are designed to test how Knight Gear would behave indoors, and how Knight Gear navigates through doors and elevators. All the following tests require one more tester to aid in opening doors and holding the elevator door open for the tester who plays the part of the user and Knight Gear. The first test would see how Knight Gear navigates through big double doors like those used

114

for entrances of buildings. The second test involves making a corner in a hallway. The third test sees how Knight Gear navigates through regular doors. The final test will test how Knight Gear handles entering and leaving elevators. These tests can be seen in the following table, table 26.

115

Test Description Outcome Comments

The user should turn on the robot. The assistant should open the big double door. The user should walk through the double doors. Knight Gear should follow the user through the double doors; it should avoid the center frame of the door if it exists in the double door used for the test.

The user should turn on the robot. Then the user should walk forward in a hallway with a 90 degree turn. Knight Gear should follow without turning into wall. The user should then go into the corner and go past it without making a sharp turn or hugging a wall. Knight Gear should follow without losing the user.

The user should turn on the robot. The assistant should open the door. The user should walk through the door. Knight Gear should follow the user through the door, it should avoid the center frame of the door as long as the user enters through the center of the door.

The user should turn on the robot. The assistant should call for the elevator and enter first while holding the doors of the elevator open. The user should walk into the elevator as far as possible as to give Knight Gear enough space to enter the elevator. Knight Gear should follow the user into the elevator; it should avoid the frame of the elevator and stop without obstructing the elevator‟s door. The user should then turn off the robot. The user should move Knight Gear such that the robot is in the back of the elevator and the user is near the door, Knight Gear should be facing towards the door of the elevator. The user should turn on the robot again while the assistant holds the door open again. The user should walk out of the elevator and have Knight Gear follow the user out of the elevator without colliding with the assistant or the inside of the elevator.

Table 26 – Indoor Performance Tests

116

8.4.7 Weight Sensors and Solar Recharging Tests

The robot is equipped with weight sensors which when tripped would not allow the robot to move. These sensors are set to trip at fifty pounds of weight. The batteries of the robot should be rechargeable by solar energy, thus equipped with a solar recharger. The test for the sensors can be done anywhere while solar battery tests should be done both indoors and outdoors. Only one person is needed to play the part of the user in these tests. The testing of weight sensors and solar recharging is listed on next page on table 27.

117

Test Description Outcome Comments

The user should insert forty-five pounds into the robot. Then they need to add a five pound weight. The robot should then be turned on. The user should advance. The robot should not move from its location. The user should then take out the five-pound weight, then move forward again. This time the robot should follow the user.

The user should check the charge of the battery before implementing this test. This part of the test should be conducted indoors. The user should have the robot follow them for a period of thirty minutes. Then the user should check the charge of the battery. Then the robot should be placed outside in the sun, and be left to charge in the sunlight for thirty minutes. The user should then check the charge of the battery again. The charge of the battery after the thirty minutes in the sun should be higher that after the thirty minutes of indoor operations closer to its base case.

The user should check the charge of the battery before implementing this test. This part should be conducted indoors. The user should have the robot follow them for thirty minutes. Then the user should check the charge of the battery, and note how much the charge has dropped. The user should then recharge the battery to the charge prior to the test. This part of the test should be conducted outside. The user should then have the robot follow them in a similar path to how they had the robot follow them indoors for thirty minutes. The charge should be then checked again and the reduction in charge noted. The change in the charge for the outdoor test should be lower as it should be charging the battery as it follows the user.

Table 27 – Weight sensor and solar recharging tests

118

8.5 Efficiency Efficiency is one of the most important aspects of testing. It evaluates how changing certain components affects the overall efficiency of Knight Gear. This can be done by measuring current using amp meter and connecting it to the power line and recording the current passing through it while Knight Gear is on the move. A Google app can record the speed of the vehicle and average speed can be obtained. At the end of each run, voltage of the motor will be recorded. Once we have the current, voltage, and speed, we can compute the efficiency level of each component and then data will be accumulated to find the efficiency of Knight Gear as a whole.

From the equations given below, we can calculate the efficiency:

, and

119

9. Engineering Consideration While building Knight Gear, it is very important to keep track of every single operation that is being performed and its possible positive and negative consequences. This is necessary because once the prototype is build; it doesn‟t approach any harmful measures to itself and to its surroundings. For instance, it is crucial to write concrete algorithms for sensor fusion for the following sensors: infrared proximity and ultrasonic proximity sensors, so that it performs strictly what is been told to it. Similar consideration is applied to Inertial Measurement Units (IMUs) where algorithms have been implemented to amalgamate gyroscope and accelerometer.

Together these fusions of sensors result in very precise deductions as to where Knight Gear is positioned and accurately follow its user. Therefore, it is vital to trust and rely on the algorithms and tested thoroughly because if Knight Gear does end up running into a person or go off track then it is absolutely not acceptable. If such mishap does happen then a user would wonder what some possible ways to overcome such scenario are. Fortunately, Knight Gear is not as big as a car neither as heavy as a printer. It is about 24 inch tall and weighs only about 5lbs. If Knight Gear deviates from the path then, there is an emergency stop button on Knight Gear which will be placed on the top of frame, making it easier for the user to identify and use it when needed. However, that will not be necessary because as soon as Knight Gear hits something or comes into collision with an obstacle or a person then it will stop motion right at that moment and at that location. This will not cause any problem in reading or storing information. Once it is switched „on‟ again, Knight Gear will accumulate all the information from accelerometer, gyroscope, GPS, beacons and inertial measurement units to find its location and start moving forward.

The unusual and unfortunate mishap of Knight Gear is not all that there is to its engineering consideration. A lot is asked about if the robot is a good fit to our world and if it will create any type of pollution that will not be bearable by the people? Two of the most important aspects of Knight Gear are the following:

Maintenance, and

Environmental Impact

How long will it operate on batteries? When does it require charging? Will it display a warning sign that battery is dying and needs charging? How much information will be recorded through the vision system of Knight Gear? How will the user extract or receive the video data in a format that is compatible to the system and at the same time easily accessible to the user? All of these questions are incorporated in maintenance section. While maintenance is a very essential to Knight Gear, it is also responsible for any environment impact that may take place.

Does Knight Gear exude any gases that could cause is potentially harmful to people around it? All the type of sensors and motors that Knight Gear is so much

120

relied upon, do they cause noise pollution that will interfere other people‟s conversation both indoor and outdoor. These are some potential aspects that need to be answered in the final segment of the prototype.

Knight Gear holds no harm to public nor does it pollute the environment. If

anything, perhaps, it may cause noise pollution because of four motors. However,

the merit of Knight Gear overcomes any of disadvantages if there is any. The

best advantage of Knight Gear is that students now will not have carry their

backpack with them. They will have Knight Gear to support them and prevent

causing any upper body pain of students.

121

10. Appendices

A. References

Sensors

"Infrared vs. Ultrasonic - What You Should Know | Member Robot Tutorials." Infrared vs. Ultrasonic - What You Should Know | Member Robot Tutorials. N.p., n.d. Web. 24 Apr. 2013.

"How to Use Pyroelectric ("Passive") Infrared Sensors (PIR)." Ladyadanet Blog RSS. N.p., n.d. Web. 24 Apr. 2013.

“Home | Product Categories | Infrared | SEN-08958." Infrared Proximity Sensor Long Range. N.p., n.d. Web. 24 Apr. 2013.

"Home | Product Categories | Flex / Force | SEN-10245." Load Sensor. N.p., n.d. Web. 24 Apr. 2013.

"Load Cells or Load Sensors How They Work?" Load Cells or Load Sensors How They Work? N.p., n.d. Web. 24 Apr. 2013.

"Compare Infrared and Ultrasonic Distance Sensors." Compare Infrared and Ultrasonic Distance Sensors. N.p., n.d. Web. 24 Apr. 2013.

"Transducer Beam Spread." Transducer Beam Spread. N.p., n.d. Web. 24 Apr. 2013.

"InvenSense Inc.: Gyroscope Evaluation Board: IDG-500EVB." IDG-500EVB, Gyroscope Evaluation Board, InvenSense Inc., CDI. N.p., n.d. Web. 24 Apr. 2013.

"Society of Robots - Robot Forum." Human Following Sensor. N.p., n.d. Web. 24 Apr. 2013.

"Society of Robots - Robot Forum." GPS Navigation Tutorial. N.p., n.d. Web. 24 Apr. 2013.

"Infrared Proximity Sensing: Building Blocks, Mechanical Considerations, & Design Trade-offs." Infrared Proximity Sensing: Building Blocks, Mechanical Considerations, & Design Trade-offs. N.p., n.d. Web. 24 Apr. 2013.

"Home | Accelerometer, Gyro and IMU Buying Guide." Accelerometer, Gyro and IMU Buying Guide. N.p., n.d. Web. 24 Apr. 2013.

122

"MB1020 LV-MaxSonar-EZ2 Ultrasonic Rangefinder." MB1020 LV-MaxSonar-EZ2 Ultrasonic Rangefinder. N.p., n.d. Web. 24 Apr. 2013.

Motors and Power Systems

"DC Motors." Motors. N.p., n.d. Web. 24 Apr. 2013.

"Robot Power Systems - Electronics & Control Projects." Robot Power Systems - Electronics & Control Projects. N.p., n.d. Web. 24 Apr. 2013.

"Robot MarketPlace - Motors." Robot MarketPlace - Motors. N.p., n.d. Web. 24 Apr. 2013.

"Motors and Actuators." - RobotShop. N.p., n.d. Web. 24 Apr. 2013

"How to Build a Robot Tutorial - Society of Robots." How to Build a Robot Tutorial - Society of Robots. N.p., n.d. Web. 24 Apr. 2013.

"Why Is Your Robots Motors Not Strong Enough? (Gearing)." Let's Make Robots! N.p., n.d. Web. 24 Apr. 2013.

"Power Transmission for Mini Robots." Power Transmission for Mini Robots. N.p., n.d. Web. 24 Apr. 2013.

.PID and Obstacle Avoidance

Naik, Ankur. Arc Path Collision Avoidance Algorithm for Autonomous Ground.Http://scholar.lib.vt.edu/theses/available/etd-01162006-112326/unrestricted/AnkurThesis.pdf. N.p., n.d. Web.

"Control Tutorials for MATLAB and Simulink -." Control Tutorials for MATLAB and Simulink -. N.p., n.d. Web. 24 Apr. 2013.

"What Are Good Strategies for Tuning PID Loops?" Control. N.p., n.d. Web. 24 Apr. 2013.

"PID Control." Let's Make Robots! N.p., n.d. Web. 24 Apr. 2013.

General

"Robot Platform | Knowledge | Wheel Control Theory." RSS. N.p., n.d. Web. 24 Apr. 2013.

"How to Build a Robot Tutorial - Society of Robots." How to Build a Robot Tutorial - Society of Robots. N.p., n.d. Web. 24 Apr. 2013.

123

"Future Tense." Future Tense. N.p., n.d. Web. 24 Apr. 2013.

Principles of Robot Locomotion. N.p.: n.p., n.d. Web.

"How Does a Robot Work? - Lesson - Www.TeachEngineering.org." How Does a Robot Work? - Lesson - Www.TeachEngineering.org. N.p., n.d. Web. 24 Apr. 2013.

"Introduction to Robots." Introduction to Robots. N.p., n.d. Web. 24 Apr. 2013.

Solar Panel

"Different Types of Solar Panels." Home Solar 101 A Homeowners Guide to Solar Different Types of Solar Panels Comments. N.p., n.d. Web. 15 July 2013.

"Solar Panel Efficiency and the Factors That Affect It | 1BOG.org." Home Solar 101 A Homeowners Guide to Solar Solar Panel Efficiency and the Factors That Affect It Comments. N.p., n.d. Web. 15 July 2013.

"Solarbotics." Solarbotics. N.p., n.d. Web. 17 July 2013.

"CleanTechnica." CleanTechnica. N.p., n.d. Web. 17 July 2013.

"Solar Charger for My Robot." Let's Make Robots! N.p., n.d. Web. 17 July 2013.

Self-sustaining Solar Powered Robot. N.p., n.d. Web. 17 July 2013

"Thread: Make Your Own Load Cell (force Sensor) from Stuff You Already

Have." Make Your Own

Load Cell

Load Cell (force Sensor) from Stuff You Already Have. N.p., n.d. Web. 17 July

2013.

Load Cell Technology. N.p., n.d. Web. 17 July 2013

124

B.Copy Right Permission emails:

Linear Technology

Steve Knoth (sknoth@linear.com)

Add to contacts

12:45 PM

To: 'do kim'

Cc: floridasales@linear.com

Hi,

That‟s fine, good luck ion your project, and thank you for asking.

Steve

Steve Knoth

Senior Product Marketing Engineer Power Products Group Linear Technology Corporation

408-432-1900 x2364

P.S.: If replying to this email, please include all previous correspondence. This retains the history and helps us keep up with your situation.

Thank you!!!

LINEAR TECHNOLOGY CORPORATION

125

******Internet Email Confidentiality Footer******

This e-mail transmission, and any documents, files or previous e-mail messages attached to it may contain confidential information that is legally privileged. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are hereby notified that any disclosure, copying, distribution or use of any of the information contained in or attached to this transmission is STRICTLY PROHIBITED. If you have received this transmission in error, please immediately notify me by reply e-mail, or by telephone 408-432-1900 extension x2364 and destroy the original transmission and its attachments without reading or saving in any manner. Thank you.

do kim (dykim12@msn.com)

4/21/13

To: orders@linear.com

To whom it may concern, I am a student at the University of Central Florida and currently working a design with a group of four people as part of the senior design course requirement. We are considering using your voltage regulator for our power supply design and would like permission to use an image from your website. The paper will not be published and is for educational purpose only. The proper citations for the copyrighted work will be included in the report. please let me know if any more information is needed. Thank you for your time and consideration, Do-yong Kim

Texas Instruments copyrights

126

Maxbotix

Siddharth,

Thanks for the email. I am glad to assist you with your questions. Please see my remarks below in black text.

You state: I need to use some of your datasheets and pictures of LV-MaxSonar EZ series. Can I get the permission to print your datasheet, detection pattern on my documentation.

You are given permission to use the images for the LV-MaxSonar-EZ sensor on your documentation paperwork for your senior design project. If you need any sensor images, on the bottom of the MB1010 product page there is a download link for all the LV-MaxSonar-EZ photos. The download is entitled "High Resolution Pictures.zip".

We thank you for taking the time to request permission to use the sensor's photos for your project.

Please let me know if you have any questions.

Best regards, Tom Bonar Technical Support of MaxBotix Inc.

127