L OW A LT I T U D E BA L L O O N E X P E R I M E N T S I N T E C H N O L O G Y

( L A B E T ) VERSION IV

DEC09-14/LABETIV_SP09

D E S I G N D O C U M E N T

FACULTY ADVISOR S AND CLIENT:

MATTHEW NELSON, DR. JOHN BASART

SPACE SY STEMS AND CONTROLS LAB

TEAM MEMBERS:

HENRI BAI

STEVE BECKERT

NATE GRINVALDS

IAN MOODIE

MIKE RAU

APRIL 14, 2009

DISCLAIMER: This document was developed as part of the requirements of a multi-discipline design course at Iowa State University, Ames, Iowa. The document does not constitute a professional engineering design or a professional land surveying document. Although the

information is intended to be accurate, the associated students, faculty, and Iowa State University make no claims, promises, or guarantees about the accuracy, completeness, quality, or adequacy of

the information. Document users shall ensure that any such use does not violate any laws with regard to professional licensing and certification requirements. Such use includes any work resulting from this student-prepared document that is required to be under the responsible charge of a licensed

engineer or surveyor. This document is copyrighted by the students who produced the document and the associated faculty advisors. No part may be reproduced without the written permission of the

senior design course coordinator.

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Table of Contents Executive Summary ............................................................................................................................................. 4

Customer Requirements ...................................................................................................................................... 4

Problem Statement .......................................................................................................................................... 4

Intended User ................................................................................................................................................... 4

Intended Use .................................................................................................................................................... 4

Operating Environment ................................................................................................................................. 5

Functional Requirements ................................................................................................................................ 5

Non-Functional Requirements ...................................................................................................................... 5

Deliverables ...................................................................................................................................................... 5

LABET History .................................................................................................................................................... 7

LABET I ........................................................................................................................................................... 7

LABET II .......................................................................................................................................................... 8

LABET III ........................................................................................................................................................ 9

Concept Sketch ...................................................................................................................................................10

System Block Diagram ......................................................................................................................................11

System Design .....................................................................................................................................................12

Chassis .............................................................................................................................................................12

Fans ..................................................................................................................................................................15

Servo Motors ..................................................................................................................................................16

Gyroscope .......................................................................................................................................................17

Accelerometer.................................................................................................................................................19

Sonar ................................................................................................................................................................20

Wireless Communication ..................................................................................................................................21

Power Supply ..................................................................................................................................................21

Microcontroller ..............................................................................................................................................22

Software ...........................................................................................................................................................23

Aircraft Control ..............................................................................................................................................24

Base Station .....................................................................................................................................................24

System Block Diagram ......................................................................................................................................25

Project Management ..........................................................................................................................................26

Resource Requirements ................................................................................................................................26

Project Schedule .............................................................................................................................................28

Appendices ..........................................................................................................................................................29

Material Properties .........................................................................................................................................29

Fan ....................................................................................................................................................................30

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Servo ................................................................................................................................................................30

Gyroscope .......................................................................................................................................................31

Accelerometer.................................................................................................................................................32

Sonar ................................................................................................................................................................33

Software ...........................................................................................................................................................34

Aircraft Model ................................................................................................................................................35

Base Station .....................................................................................................................................................37

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Executive Summary The Low Altitude Balloon Experiments in Technology (LABET) project has had a strong history in the Space Systems and Controls Lab (SSCL) on the campus of Iowa State University. LABET was formed as a way to demonstrate the SSCL's work with helium balloons without the necessary setup time associated with High Altitude Balloon Experiments in Technology (HABET). The LABET setup consists of an aircraft equipped with electronic hardware and an attachment point for a helium balloon. The balloon provides roughly 90% of the aircraft’s lift and allows the aircraft to be wirelessly controlled throughout Howe Hall atrium or other indoor open areas. To date, three successful LABETs (LABET I, II, and III) have been built, all with unique qualities which will be addressed later in this document. A project team consisting of five students from Iowa State University has been established to design, test and build LABET IV. The team is comprised of students from the classes EE 491 and Engr 466. This team is made up of students in the disciplines of electrical engineering, computer engineering, mechanical engineering, and materials engineering. The team is under the direction of advisors Matthew Nelson, Chief Design and Operations Engineer of the SSCL and Dr. John Basart, retired professor in Electrical and Computer Engineering. In the following document, the project team will outline describe the design process of LABET IV. This document will discuss the general problem statement, intended use, system requirements, subsystem details (requirements, tradeoffs, description, testing, and challenges), and project management.

Customer Requirements

Problem Statement

Iowa State University’s Space Systems and Controls Lab builds and tests various platforms for both academic and scientific missions. One of these platforms is the LABET. LABET is a platform for testing controls and other equipments using smaller and cheaper latex balloons. Three previous incarnations of the LABET project have already been constructed. Prior LABETs have lacked quality in flight control and maneuverability, solid construction, or an efficient user interface. Previous aircrafts lacked any ability to fly autonomously, limiting the knowledge that can be gained from their flight. LABET is also used as a demonstration tool for the SSCL lab and the college of engineering.

Intended User

The intended user for this product is the Space Systems and Controls Lab, located in 2362 Howe Hall. The aircraft will be operated by a single user from a base station. The base station will have complete control over the aircraft via wireless communication.

Intended Use

The SSCL has multiple intended uses for this product. The main use for LABET IV is as a promotional tool to be displayed during tours or events taking place in the Howe Hall atrium. A second use for LABET IV is as a test bed for future electronics. The SSCL will use LABET IV as a learning tool where students from a variety of engineering disciplines such as aerospace, materials, mechanical, computer, and electrical can work together to improve upon a single design.

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Operating Environment

LABET IV will be operated in a controlled environment. Specifically, the aircraft will primarily be flown in the atrium of Howe Hall on the campus of Iowa State University. The aircraft will not be operated in high winds, but will encounter slight turbulence due to the building’s HVAC system. The aircraft will be operated in a confined space and will be subjected to walls, ceilings, railings, and sharp corners, all of which could damage both the aircraft and the balloon.

Functional Requirements

FR-01: LABET IV must weigh less than 1.5 pounds FR-02: LABET IV must have minimum fly time of 20 minutes FR-03: LABET IV must have yaw control FR-04: LABET IV must have altitude control FR-05: LABET IV must have ability to traverse forward and backward FR-06: LABET IV must have ability to be controlled wirelessly FR-07: LABET IV must have ability to land autonomously on a table from 4 meters above FR-08: LABET IV must have attachment point for 100 gram balloon

Non-Functional Requirements

NFR-01: LABET IV design should be aesthetically pleasing NFR-02: LABET IV design should be innovative NFR-03: LABET IV should be easy to control NFR-04: LABET IV should be completed with thorough documentation

Deliverables

The deliverables for LABET IV are a combination of class-specific and project-specific requirements. Website The project website will be constantly updated throughout the project duration. This website will be used to display the current status of the project and to host all documentation. Weekly Reports Weekly reports are a requirement for both classes (491 and 466). They will consist of two components – hour tracking and project status. Each week, an individual’s hours will be accounted for and added to a running total. The hours will be classified into general categories such as classroom, meetings, research, documentation, and other categories as the project progresses. Weekly reports will also consist of a short summary of the previous week on a group and individual level. Project Plan The project plan will be a document outlining the project. The project plan discusses the need of the project, requirements, market research, design strategies, and project management. Project Plan Presentation The project plan presentation will be a PowerPoint presentation given in class summarizing the project plan document.

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Design Document The design document will be a report outlining the complete design process for the project. This document will discuss the project on a component level and detail how each component will be incorporated into the system. More details on the design document will be available at the end of the spring semester. Design Presentation The design presentation will be a PowerPoint presentation given in class summarizing the design document. Bound Reports The bound report will be a document summarizing the entire semester’s work. More details will be available at the end of the spring semester. Functional LABET IV A functional LABET IV will be delivered in December 2009 in accordance to the requirements outlined in this document. In addition to a functional aircraft, the necessary firmware, software, wireless control, base station, and any necessary documentation to operate the LABET IV will also be delivered.

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LABET History

LABET I

LABET I was the original version of the Low Altitude Balloon Experiments in Technology project completed at Iowa State. LABET I featured a single vertically mounted propeller, fit within a Styrofoam chassis. Two rudders, controlled by a servo, allowed for directional control. The landing supports are simply thin pieces of fiberglass bent with a string (analogous to a hunting bow). The user-interface was a simple joystick controller.

Figure 1 - LABET I

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LABET II

LABET II followed LABET I by a year, and represented vast improvements in design and functionality. LABET II uses a carbon fiber triangular chassis with two fixed, vertically mounted motors. As a whole, the device weighs less than one pound. Yaw control is provided by a horizontally mounted propeller. Pitch control is achieved by a servo that is attached by strings to the balloon. The aircraft is controlled wirelessly by custom software. The software displays the battery status, speeds of both the motors and the propeller, and shows the status of the gyro. LABET II is presently the LABET version showcased at various ISU events (such as First Lego League).

Figure 2 - LABET II

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LABET III

The LABET III team was tasked with finding an indoor as well as outdoor solution for a low altitude balloon. To satisfy this requirement, the design needed to be heavy enough to withstand outdoor conditions (namely, wind). The device weighs approximately six pounds, and uses four motors: two mounted vertically and two mounted horizontally. Each of these motors provides about three pounds of thrust, enough power to lift the device without a balloon. LABET III has been tested without a microcontroller, meaning that the motors were controlled manually. This made controlling the aircraft difficult, and LABET III has never successfully flown. Presently, LABET III is still an active project, but has taken a secondary priority to other projects.

Figure 3 - LABET III

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Concept Sketch

Figure 4

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System Block Diagram

Figure 5 - System Block Diagram

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System Design

Chassis

Chassis Design

Figure 6 - Model of Frame (two motor, Cradle)

Several chassis' were considered for the final design, and the two-motor, “Cradle” chassis design emerged the best based upon its combination of stability, light weight, and ease of manufacture. Table 1 below shows the advantages and disadvantages of the various chassis'. Table 2 shows the trade study that was completed for the considered chassis’. As shown, the highest overall score went to the two motor, Cradle design. A full size foam prototype of this chassis has been built and demonstrated areas where fabrication may be difficult. The prototype also shows provides a visual representation of how the balloon will sit on the chassis and where/how the electronics will fit.

Chassis Design Advantages Disadvantages

Two motor Balloon Cradle

-Lighter weight -Uses less power -May provide greater stability than two motor with prop

-Less control than Three Motor -Less powerful lift

Three motor Balloon Cradle

-Most stable design -Most powerful

-Heaviest design -Three motors mean more batteries

Two motor, one prop -Lighter weight -More control than other two motor design

-Less powerful than three motor design

One motor, two props -Lightest design -Will require less battery power

-Least amount of stability

Table 1 - Advantages/Disadvantage

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Chassis Requirements

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Scoring Range: 1 to 5 1, 3, 5, or 7

1.5 lb total weight limit 5 5 1 5 7

Easy Balloon Attachment point 3 5 5 5 5

Easy mounting of electronics 4 5 5 5 3

Fly time (20+ mintues) 5 5 1 5 7

Stability 4 5 7 5 3

Traverse Forward and Reverse 3 5 5 3 1

Altitude Control 3 7 7 7 5

Autonomous landing from 4 meter altitude 5 7 7 5 5

Final Scores: 176 144 165 152

Table 2 - Design Matrix Chassis Materials After the structure was chosen, the choice of material was the next question to answer. A comprehensive list of materials was initially considered and is documented in the Project Plan Report. The list of materials was narrowed considerably, once material properties, material availability, and price were taken into account. The team decided to move forward with using acrylonitrile butadiene styrene (ABS) as the material of choice. The composition of ABS varies depending on the material properties desired, but ABS typically consists of between 15-35% arylonitrile, 5-30% butadiene, and 40-60% styrene. Each individual component contributes to the overall structures of the polymer, where acrylonitrile and styrene provide stiffness while the butadiene (synthetic rubber) provides flexibility, good impact strength, and toughness. As mentioned, a key deciding factor was the cost of the material. A sheet of ABS with dimensions 0.060” x 24” x 48” cost approximately $11, while a similarly sized sheet of fiberglass costs upwards of $70. For more details, consult the Material Properties Appendix Fabricating fiberglass in-house via the Materials Preparation Laboratory in Howe Hall was also an option, but was dismissed after some experimentation (at least for the majority of the chassis. Making fiberglass in-house jeopardizes the uniformity of the finished product and could potentially negate the effectiveness of the fiber. In addition, considering the cost of glass cloth, simply purchasing mass-produced material would be more cost effective. Carbon fiber can also be made in house, but similar advantages and disadvantages arise as with the fiberglass. At the time of the writing of this document, the chassis has not yet been built. A Dremel tool, as well as other tools, will be used to cut out the various pieces of the chassis. The cut parts will be glued together using glue specifically intended for ABS. Assuming the ABS sheet arrives in a timely manner, the chassis will be built before the end of the semester. Testing of the Chassis When the LABET is in flight, the “worst case” scenario is the balloon deflates, and the LABET falls from a height of potentially several meters. A simple test of the strength of the chassis would be to simply mount weights where the motors are to be placed, and drop the chassis from several feet. A

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problem with this approach, however, is that it is destructive, thus, another test needed to be developed to successfully test the chassis. Finite element analysis (FEA) can be used to model the stress/strain behavior through the chassis under certain loads. While at the time of this writing, FEA is not complete. Tentatively, this will be performed in Solidworks FEA tool called COSMOS. Iowa State University also provides FEA software called ANSYS, which is a much more robust software package than the tool in Solidworks. A simple test that can be conducted on a piece of scrap material is a simple 3-point bend or 4-point bend test. This allows the tester to get an idea of the mechanical loads that the material can withstand before fracture.

Technical Challenges The greatest technical challenge when fabricating the chassis will be the creation of the motor mounts (Figure 7 below). The fans will need to rotate in two axis, thus two rings, one directly outside the other will be created. Each of the rings will include two swivel points that will allow the fans to be gimbaled At the time of the writing of this document, the method of fabrication is to simply create the motor mount as modeled either out of ABS or (if the ABS cannot be made to dimensions), foam. The swivel points must be low friction, thus lubricant will be used on these joints to allow for smooth rotation of the fans without loss of power or speed.

Figure 7 - Frame with Balloon

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Figure 8 - Motor mount

Fans

Requirements The fans for this project serve two purposes, to provide lift for ascent and descent and to provide horizontal thrust for complete three-dimensional control. The fan motor speed must be variable and provide adequate thrust to maintain constant vertical lift or ascend while at a maximum thrust vector, e.g. at a maximum horizontal thrust angle. If available, the two fans should have opposing rotation to negate rotational torque caused by the motor and fan inertias. If opposing fans cannot be found, a gyro sensor must be utilized to stabilize yaw control via thrust vectoring. The minimum required thrust of each fan is a function of the total aircraft weight. As per the project requirements, the balloon will lift 90% of the total weight, leaving the remaining 10% of lift provided by the fans.

𝑇𝑜𝑡𝑎𝑙 𝐹𝑎𝑛 𝑇𝑕𝑟𝑢𝑠𝑡 = 𝐴𝑖𝑟𝑐𝑟𝑎𝑓𝑡 𝑤𝑒𝑖𝑔𝑕𝑡 ∗ (.1) This total fan thrust will be the average thrust provided by 2 fans.

𝑇𝑕𝑟𝑢𝑠𝑡 𝑝𝑒𝑟 𝐹𝑎𝑛 =𝑇𝑜𝑡𝑎𝑙 𝐹𝑎𝑛 𝑇𝑕𝑟𝑢𝑠𝑡

2

With a maximum weight of 1.5 pounds, the minimum thrust provided by each fan is approximately 34 grams. Tradeoffs Three electric ducted fans from GWS were evaluated for use in this project. The first two use the same fan (1630x6) with different motor sizes. The fan information shown in the Fan Appendix was provided by GWS. The first motor is the CN12-RLC, with a maximum thrust of 87grams at 8.4 volts with a minimum thrust of 53 grams at 6 volts. The second motor is the CN12-RXC, with a maximum thrust of 74grams at 12 volts with a minimum thrust of 53 grams at 9.6 volts. The third ducted fan is the GW/EDF-55-150. This is the fan that was chosen for component testing due to its greater range in operating voltage, lower minimum thrust output, and greater efficiency in the operating range of 34 grams of thrust (as shown in the Fan Appendix). Subsystem Description In order to build an accurate motor control, an equation must be found relating the input parameters to the fan output. Using the vendor information, a plot of input voltage versus output thrust was created as shown in the Fan Appendix. A linear trend line was applied representing 99.36% of the data points and the motor equation was found.

V = 0.0572T + 1.761

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Testing Testing will be conducted with the EDF-55-150 fan from GWS. Two important features will need to be extracted from testing; an accurate thrust output versus supply voltage equation and motor and fan rotational inertia values. A simple testing rig, as shown below, will be built to incorporate a load cell to measure thrust force from the ducted fan. This information will be recorded as well as the voltage and current data points and plotted versus the thrust force.

Figure 9 - Fan Test Stand

If the vendor, GWS, cannot provide the rotational inertia values for the fan and motor, a test will need to be set up to find these values. If this is the case, the motor will need to be removed from the duct housing and the fan removed from the shaft. A known torque will then need to be applied to the motor and ran at peak RPM. The motor input parameters will need to be plotted to extract the peak torque and frictional torque. After further calculations, the angular acceleration and motor inertia can then be found. This process can then be repeated with the fan to obtain the fan rotational inertia values. Technical Challenges The greatest technical challenge with the fans will be obtaining the rotational inertia values for obtaining mathematical models of the system. The proper fan tests will be important to build accurate control models to optimize manual and automatic flight controls.

Servo Motors

Requirements As described in the Fans section, two fans will be employed to provide the lift and horizontal control of the aircraft. The fans will be mounted initially with the thrust employed in the z direction. In order to provide horizontal control these fans will be built have the ability to be gimbaled. This is done by installing the fans in rotational rings built directly into the chassis. To provide the rotation and stabilization of the rings and fans four servo motors will be employed. There will be two servos for each fan, one providing x axis rotation, and the other y axis rotation. As the aircraft has a strict weight requirement, the servos employed must be as small as possible in both weight and volume. However, this requirement is met only after ensuring the servo has enough power to provide the torque and speed needed to rotate and maintain the fan position. Tradeoffs There are a wide variety of servo motors available in the consumer market. Servo motors can range from $10 dollars to well over $1000. These high priced servos are employed in much different

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applications such as car brakes, military guns, or satellite tracking antennas. Such high end servos are well outside of the project teams’ monetary budget as well as the aircrafts weight budget. Standard RC servos similar to the ones that will be employed on the LABET IV aircraft can range from $10 to ~$100. The budget of the team limited the selection of servos to the $10 to $20 range. The main two limiting factors in servo selection are servo weight and the torque that it can provide. As shown in the Servo Appendix of potential servo motors, as weight and volume of the motor increases the torque and speed the motor provides will also increase. Subsystem Description The Electrify ES350 Nano servo has been selected to be used on the aircraft. This servo was selected as it is the cheapest servo available as well as being close to the lightest. The ES350 will run on a 5 V supply while providing approximately 1.3 kg.cm torque at a speed of 0.13 seconds for a rotation of 60 degrees. The important factor in selecting this servo is that it weighs only 9 grams, creating a total servo system weight of 36 grams. This equates to only 5.15% of the aircrafts total weight budget. System Integration The four servo motors will be integrated into the aircraft system through the PIC microcontroller sending the servos a PWM signal. To control the servo, it is commanded to a certain angle, measured from 0 degrees. A series of pulses is sent by the driver to the servos to control this angle. The ON time of the pulse indicates the angle to turn to; 1ms = 0 degrees, 2ms=120 degrees (maximum angle). This PWM signal is generated by the microcontroller using the information provided by the aircraft pilot. The actuator arm of the servos will then be connected to their respective gimbaled rings to control and maintain the fan position. Testing The main aspect of servo testing will be to ensure that the servo motors can output enough torque to rotate and maintain fan position. It is important to note that the servos must also do this quick enough to guarantee that the aircraft has quick response to pilot control. In order to test the servos a servo control circuit will be employed as the microcontroller programming will not be complete in time for servo torque testing. This control circuit will be provided by the SSCL, as the SSCL already has this type of circuit available. The control circuit will take a dc voltage input and convert it to a pulse to be sent to the servo motor. While some testing can be done before chassis completion the chassis must be fully built before the team can be positive the testing is rigorous enough. This is to ensure that the servo can not only provide enough torque to move the weight of the fan but also to counter and friction provided by the chassis design. Technical Challenges The biggest technical challenge that will be faced is positioning of the servo motors within the aircraft. The servos must be able to provide the rings with their rotational position without interfering with any other components. Most likely one servo per fan will be attached directly to one of the gimbaled rings. This challenge provides another incentive for chassis fabrication to be first step in aircraft construction.

Gyroscope

Requirements In order to control rotation in the yaw axis of the aircraft, a sensor is needed which measures such a rotation. A gyroscope has been selected to measure this rotation. The gyroscope used in the aircraft must be powered by 3.3 Volts, draw little current, and measure rotation rates up to 50°/s. As the aircraft will need to be stabilized in two axes, a dual-axis gyroscope or a combination of single-axis gyroscopes will need to be implemented.

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Tradeoffs There is a wide variety of gyroscopes on the market today, ranging from $~40 to upwards of $1000. The project group’s budget initially limited the choices to only a few. Most gyroscopes researched satisfied the 3.3 Volt input and the sampling sensitivity requirements. Only one reasonably priced gyroscope was dual-axes – the Invensense IDG-1215. Other gyroscopes would require two units, increasing complexity, cost, and power consumption. The IDG-1215 was found to have the best combination of functionality and cost of all gyroscopes researched. Subsystem Description The Invensense IDG-1215 gyroscope has been selected to be used in the aircraft. This dual-axis

gyroscope has a full-scale range of ±67⁰/s and 15mV/⁰/s sensitivity. The sensor also contains integrated low-pass filters and an on-chip temperature sensor which can be used to compensate reading based on changing environments. The IDG-1215 runs on a 3.0 Volt supply and draws 7 mA current during typical use. The data output by the IDG-1215 is an analog voltage signal proportional

to the rate of rotation and follows the equation OutputVoltage VREF

Rotation RateSensitivity

. VREF

is an internal reference voltage of 1.35 Volts. The gyroscope has an auto zero pin which, when pulled low, resets the zero-rate voltage to VREF. This functionality will be utilized when the aircraft is powered up in order to set the proper output bias. System Integration The IDG-1215 gyroscope will be integrated into the system by way of the Silicone Horizon™ IDG-650 Bare Breakout Board. This board, while intended to be used with the IDG-650, will also work with the 1215, as the footprint and pin outs are identical. This board contains a 3.0 Volt regulator, bypass capacitors, and an MCP6004 opamp chip used to buffer the outputs. Since this board is intended for use with a different sensor, 4 jumper pads will need to be soldered. These pads are indicated in the Gyroscope Appendix. Also, due to the orientation of the IDG-1215, it will have to be mounted vertically in order to sample rotation in the roll and yaw planes. This will be accomplished by using a 90 degree header on the breakout board. The breakout board will have input/output connectivity according to figure in the Gyroscope Appendix. Testing The IDG-1215 will be thoroughly tested before any system integration. This testing will consist of range testing (what rates can the gyroscope measure), drift testing (how much does the gyroscope drift over time), and temperature testing (how does a normal increase in temperature effect the measurements). This will of course take place after the device is installed on the Silicon Horizon™ breakout board and a general familiarity is established. After the project team is satisfied with the isolated testing, the gyroscope will be integrated into the aircraft along with other sensors. Technical Challenges As with most analog sensors, electronic noise is often an issue. The gyroscope may need to be digitally filtered in addition to the analog filtering taking place on the board. A second problem common amongst many low-cost gyroscopes is drift. Over time, the sensors "0" measurement moves from its original location. This characteristic will be analyzed as the testing is completed. Finally, it will be technically challenging to properly assemble the sensor breakout board as the gyroscope and many other components are very small. The project team will maintain backups of components incase damage is done during assembly.

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Accelerometer

Requirements In order to measure the aircraft’s velocity in all three translational degrees of freedom, the acceleration will need to be measured in all three axes. To maintain a standard in supply voltage, the accelerometer must be powered by 3.3 Volts. It must also be able to measure accelerations of approximately ±5g. Tradeoffs There are many affordable analog and digital accelerometers on the market today. Most accelerometers have very similar performance. From research, the largest tradeoff amongst accelerometers is the decrease in sensor noise gained by using a digital sensor at the cost of increased complexity. Subsystem Description The LIS3LV02DL is the current selection to fill the need of accelerometer. This is a 3-axis digital sensor which runs off of 3.3 Volts and draws a typical 0.65 mA. This accelerometer has both I²C and SPI functionality along with a high (±2 g) and low (±6 g) sensitivity. The output measurements are obtained by reading the OUTX_L (LSB) and OUTX_H (MSB) register for each axis using the digital bus of choice. System Integration The LIS3LV02DL will be integrated into the system using the STEVAL-MKI009V1 evaluation board. This board will simplify the integration and testing of the device by transforming the 16 pin land grid array package to a dual inline package as shown in figure 10.

Figure 10 - STEVAL-MKI009V1 Evaluation Board

The evaluation board will connect directly to the microcontroller by way of the either I²C bus (CS, SCL, SDA) or the SPI bus (CS, SPC, SDI, SDO) digital bus. The bus selection will be made after initial component testing. Testing The LIS3LV02DL will be thoroughly tested before any system integration. This will need to be done in combination with a microcontroller which supports I²C or SPI. The testing will consist of full range testing to ensure the sensor will be able to properly measure all possible accelerations, temperature testing to observe the effects of temperature on the measurements, and drift testing to observe the accuracy of the sensor over time. During the testing, the different functionality of the LIS3LV02DL can be investigated, such as full scale range and sampling frequency.

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Technical Challenges The greatest technical challenge associated with the accelerometer will be establishing communication between the sensor and microcontroller. This was previously mentioned as the downside to digital interfaces. This difficulty will be confronted early in the component testing stage and, if necessary, the accelerometer can be replaced for a more user-friendly model.

Sonar

Requirements A sonar sensor will be employed on the LABET IV aircraft to assist in the autonomous landing feature. This sensor must be able to detect an object from at least 4 meters as this is the minimum distance the aircraft must be able to autonomously land from. This sensor must run on a supply voltage of 3.3 V while drawing about 2 mA of power. Tradeoffs Initially the project team thought it could employ an infrared sensor to more accurately gauge the distance from landing. However, because of the operating environment it soon became apparent that infrared was not a viable option. Without construction of an elaborate base station infrared could not meet the 4 meter landing requirement. On the other hand, this created a problem as there are very few commercially available sonar sensors designed for small applications. The sonar sensors that are available are ~$25, this is slightly more than the project team would like to spend on this sensor but is still within the teams’ budget. It was decided to employ a Maxbotix sonar sensor as these have been used on previous projects in the SSCL. Maxbotix makes several models of this sensor with progressively narrower beam angles for different object size detection. The tradeoff with employing a smaller beam angle is that the price of the sensor increases. The project team’s requirement is that the aircraft can land on a table. As this is a fairly large object it was decided to employ a cheaper sensor at the expense of better object detection. Subsystem Description An Ultrasonic Range Finder - Maxbotix LV-EZ1 will be employed on the LABET IV aircraft. The sensor is a 42 kHz ultrasonic sensor. It will operate on a 3.3 V supply and draw a current of 2 mA. The small current draw is beneficial as it will consume very little of the aircrafts power budget. The sensor can read at a rate of once every 50 ms, this is well within the aircraft descent speed. System Integration The sonar sensor will accept a RX/Enable signal from the microcontroller. This signal will allow for the sensor to be turned off and not drain power when the aircraft is not in landing mode. LV-EZ sensors have three types of outputs. They can employ serial, PWM, or analog outputs. Through discussion it was initially decided that it will be easiest to use the analog output feature. This output measures at a rate of 10 mV/inch. This output will have to be received by the microcontroller and converted to a distance and ultimately a descent rate for the aircraft. Testing The LV-EZ1 will undergo thorough distance testing before it is employed on the aircraft. It will be tested for all distances from 5 meters down to its minimum distance reading of 1 cm. The output signal will be monitored throughout testing to ensure that the output matches the actual distance measured. Once the microcontroller is completed the sensor will then be tested to ensure proper system integration.

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Technical Challenges One key technical challenge will be the mounting of the sensor on the aircraft. The sensor will have to be mounted on the z-axis in such a way that it can provide a stable reading to the microcontroller. Receiving a stable reading from the sonar sensor is essential as it will ultimately be used to set the descent rate for the aircraft.

Wireless Communication Requirements The wireless communication scheme used must be able to transmit data in both directions – to and from the aircraft. This will be important in sending control signals to the aircraft and receiving diagnostic information back from the aircraft. Tradeoffs Tradeoffs in the communication occur between transmission frequencies, data transmitted, and hardware used. Previous LABETs have used the 433 MHz frequency and experienced noise issues. The project team has been recommended to use a different frequency. There exists a tradeoff as far as what information is transmitted from the base station to the aircraft. This data could either be direct controls to the fans and servos or desired motion for the onboard microcontroller to translate. Finally, whether to use one single transceiver chip or a pair of a dedicated transmitter and a dedicated receiver can be used. Subsystem Description The project team has cleared many of the tradeoffs surrounding the wireless communication up to selecting the hardware. The project team has decided the hardware will transmit desired movement from the base station to the aircraft. This puts less stress on the robustness of the wireless link as it does not depend on reliability of data being transmitted both ways (fan control to the aircraft and sensor data from the aircraft). Finally, the project team hopes to use a single transceiver over the combination of multiple chips. This is in the hopes of simplifying the system. The SSCL has on hand multiple communication chips to be tested. After preliminary testing, a experienced decision can be made regarding the wireless communication hardware. Testing The wireless link will undergo isolated testing before integration with the system. This will consist of range testing, signal quality tests, and bandwidth testing. These tests will be conducted in the operating environment of the aircraft - the Howe Hall atrium. Technical Challenges The greatest challenge with the wireless communication will be initially establishing the wireless pairing and integrating the wireless hardware with the microcontroller.

Power Supply

Requirements The power supply chosen must be able to provide the appropriate voltage and current to the aircraft for a minimum of 20 minutes (FR-02). The power supply must also be relatively light weight. To maximize the power to weight ratio, lithium-polymer batteries will be used. A power supply with 7.4 Volt output will be required, as the fans necessitate this voltage.

LABET IV PAGE 22

Tradeoffs The major tradeoff in batteries is capacity for weight. The weight of similar batteries is also slightly higher if the battery has a greater maximum discharge current. Subsystem Description The specific batteries will be chosen after aircraft components are chosen and tested for their power consumption. The specific batteries chosen will need to supply 7.4 Volts, roughly 4000 mAh, with a maximum current discharge of 15 Amps. System Integration The batteries will be connected as a parallel connection of two series batteries for a total of 4, 3.7 Volt cells. This will provide the necessary 7.4 Volts and a capacity of 3500 mAh to 5000 mAh. Since each component cannot handle 7.4 Volts, the batteries will be wired to voltage regulators. These regulators will power all the sensors and servos. The two fans will be connected directly to the battery. Testing The batteries will be tested for capacity and supply voltage over the entire capacity of the battery. Special circuitry can be implemented which will record this information. Technical Challenges The greatest technical challenge associated with the batteries will be finding the correct tradeoff between weight and capacity.

Microcontroller

Requirements The purpose of the microcontroller is to be used as the heart and brain of LABET. The microcontroller is used for the controlling communications, automatic control, stability, and various debugging. The microcontroller shall be used for data transmission and communication with the base station. The microcontroller shall be used as an interface to control or poll the sensors, servos, and fans. The microcontroller shall be used to perform the algorithm for automatic landing Tradeoffs Several families of microcontrollers were considered. These families are: MIPS, PIC, ARM, MSP430, PowerPC. Several conditions must be met for choosing a processor: Cost (both the toolset and the processor itself), ease of use (both in compiling and fabrication), availability, helping resources (community, documentation), power consumption, how powerful. Only the 16 bit process families are considered. Scale is 0-5 with 5 being a score that is desired. Note, these are all not independent variables.

Proc Cost Ease of use

Availability Helping Power Con.

Powerful Total

MIPS 5 5 3 3 3 5 24

PIC 5 5 5 5 5 5 30

ARM 2 2 1 1 5 5 16

MSP430 3 3 2 3 5 5 21

PowerPC 3 2 1 3 2 5 16

Table 3 - Microcontroller selection

LABET IV PAGE 23

It is clear that the PIC is used. The reason why it has perfect marks is the lab has these processors in stock, so there is no need to purchase. The toolset already exists on the computers, and there are developmental and demo boards that can be used. The supervisor of the lab is also a resident expert on the PIC microcontroller. Subsystem Description The microcontroller is a 16 bit microcontroller that runs at 16 MIPS, has 128 KB of program memory, 8192 RAM bytes and operates at a voltage of 2 to 3.6V. There are 85 IO pins, and 100 total pins. The microcontroller can run at 8 MHz, or 32 KHz. It also includes nanoWatt features such as fast wake and fast control. There are 2 UART, 2 SPI, and 2 I2C buses that can be used for digital communication. There are 16 10 bit A/D 500 ksps converters. There are also 5 PWM outputs that can be used to power motors and fans. There are also 5 16 bit timers. The microprocessor is based on the Harvard architecture. Testing The microcontroller will be tested to ensure it boots up properly. The remainder of testing is component dependent and outlined in the previous sections. Technical Challenges A key challenge is to make sure the connections of the microcontroller and peripherals are correct, and the software can talk to the peripherals correctly. Another technical challenge is to make sure that the microprocessor will have a steady input voltage and that the core voltage remains at 2.2v. If the battery is finicky, the input voltage may vary and if there is a large drop or hop, then the microprocessor has a chance to perform a hardware reset. This can be catastrophic if this happens during descent. Past variables are reset and the LABET will not have enough time to respond and will be destroyed.

Software

Requirements The software is the implementation of the algorithms that will be developed. It will reside in the microprocessor and will execute the software. The software shall be responsible for implementing the algorithms used for communication, automatic landing, balancing, and debugging. The software shall be written in C. The software shall be compiled using the built in toolchain for the PIC microcontroller. Subsystem Description The software shall interface with the peripherals by using a driver interface. The driver interface is used to convert meaningful data into data that can be used by the peripherals. The main run of the software will consist of a state machine with two states: manual control and automatic control. While in the manual control, the communication driver will facilitate the data communication between the base station and the aircraft. Data conversion will be done there. Then the algorithm for stability will use the sensor driver in order to poll data from the sensors and return a meaningful value (such as Newtons, meters, or radians) instead of the voltage equivalents returned by the sensor. Then the control will read these sensors, as well as the input from the base station, to apply the necessary angles and thrust force to the motors and fans. The fan and motor driver will convert those values into values that can be directly fed into the fans and motors. The drivers are necessary interfaces in order to be able to meaningfully and efficiently talk to the peripherals. There are also debugging and health monitor modules that will be able to talk with the sensors and fans/motors in order to check if they are working correctly, and give information to the base station for debugging. A class diagram can be seen in the Software Appendix.

LABET IV PAGE 24

Testing Testing will be done by performing requirements based verification. Black box and white box techniques will be used in order to test a requirement and verify the requirement is met. A test harness will be written in order to facilitate the white box testing on the target. Test cases will be written for each requirement, and test procedures will be written for each test case. Techniques employed will be equivalence partitioning, model testing, regression testing, and code coverage. Technical Challenges One challenge is to interface the software with the peripherals and communication devices. Running processes in parallel will be a challenge due to the single thread execution of the processor. Running parallel processes has the advantage if we want to run a balancing algorithm while we control the aircraft.

Aircraft Control

The aircraft will be controlled through embedded software on the microcontroller. This software will input the desired directional thrusts and output the necessary fan thrusts and servo angles to accomplish this movement. PID controllers will be used to maintain stability and produce a fast response time. The initial control schemes will be made in MATLAB Simulink. A preliminary aircraft model has been created. As the fabrication of the aircraft progresses, the model will improve in order to better capture the dynamics of the structure. As fans, servos, and sensors are tested, these components will also enter the Simulink model until every aspect of the aircraft is included. Below in the Aircraft Model Appendix is the current aircraft model. This model takes inputs of fan thrusts and servo angles and outputs the response of the aircraft. This model captures the basic dynamics of the aircraft but is not completely sufficient. The model does not compensate the servo angles if the aircraft is off its roll axis. The model also lacks accounting for any sway in the aircraft. These issues will be addressed as the modeling becomes more accurate.

Base Station

Requirements A base station will be constructed for local control of the aircraft. This base station will send and receive signals to/from the aircraft. The station will take input from a human pilot and send positional direction to the aircraft. The base station will also receive aircraft status information.

Tradeoffs Several types of stations have been discussed. These include everything from a simple joystick to running a controller through a computer. The tradeoffs between these designs are the ease of use versus ease of construction. While a simple joystick would be the easiest to build it would not provide the quality of feedback and control the team desires for the pilot. A computer program with a graphical user interface would be the best option in terms of control and aircraft feedback. However, this type of interface may be too difficult to construct properly given the time constraints of the project.

Subsystem Description The base station will consist of a computer connected to a transceiver. This transceiver wireless communication section) will send the aircraft positional directions. The microcontroller will then interpret these directions and convert them to fan thrust and fan angles. The computer will have a

LABET IV PAGE 25

GUI that will display important information to the pilot such as battery power, fan speeds, and sensor feedback. The pilot input will be through computer keyboard control or through a controller that is run through the computer.

Testing The base station programming will be thoroughly tested before it is tested with the actual LABET aircraft. Sample feedback will be sent into the station to ensure that it can receive the information from the aircraft. It will also be tested to ensure that pilot input translates directly to desired aircraft movement before it will be run with the aircraft itself. Once separate aircraft and base station testing are complete, short controlled flights will be done to ensure no interfacing problems occur.

Technical Challenges The key technical challenge to base station construction will be how to take input from the pilot. It is the teams desire to use a controller (perhaps an xbox controller) to take this input. Few team members have experience in this type of work so it may be difficult to translate this type of input into information that can be sent to the aircraft.

System Block Diagram

Figure 11 - System Block Diagram

B reakout B oard

B reakout B oard

+

B attery

7.4 V

-

Fan x 2

6A x 2

M icrocontro ller

D river

3 .3 V

R egulator

5 .0 V

R egulator

Servo x 4

_A x 4

D river PW M S ignal x 4

PW M S ignal x 2

G yroscope

ID G -1215

2-A xis

(7m A )

A ccelerom eter

3-A xis

(0 .8m A )

LV-M axSonar

Sonar

(2m A )

W ireless

Transceiver

(~10m A )

3.3 V

Supply

3.3 V

Supply

3.3 V

Supply

3.3 V

Supply

3.3 V

Supply

5.0 V

Supply7.4 V

Supply

System D iagram (3/31/09)

A nalog YO U T

A nalog XO U T

A nalog Tem pO U T

A nalog VR EF

G N D

A nalog S ignal x 4

A uto Zero C ontro l S ignal

R D Y/IN T

SD A /SD I

SD O

SC L

D ig ital S ignal x 4

A nalog O ut

R X/Enable

LABET IV PAGE 26

Project Management

Resource Requirements

The LABET IV project requires several resources for successful completion. These include the labor of the team members, hardware for the aircraft, and a computer for the control system.

Component Cost Number Total Cost

Motors/Fans $12.00 2 $24.00

Servos $18.00 4 $72.00

Chassis Material $0.00 1 $0.00

Balloon $0.00 1 $0.00

Sonar Sensor $13.00 1 $13.00

Accelerometer $18.00 1 $18.00

Gyro Sensor $20.00 1 $20.00

Wireless Transmitter $14.00 1 $14.00

PIC $8.00 1 $8.00

Batteries $14.00 4 $56.00

Ground Station $0.00 1 $0.00

Total Project Cost $225.00 Table 4

LABET IV PAGE 27

Task Name Cost

Steve Beckert Ian Moodie Mike Rau Nate Grinvalds Henry Bai

Totals, @ $20/hour $23,620.00 262 262 262 133 262

Documentation $3,800.00 38 38 38 38 38

Project Presentation 4 4 4 4 4

Project Plan 9 9 9 9 9

Design Document 12 12 12 12 12

Website 1 1 1 1 5

Poster 5 5 5 5 1

Final Report 7 7 7 7 7

Research $6,600.00 72 72 71 43 72

Chassis Design 4 4 22 18 2

Fans/Motors 4 4 18 2 4

Servos 4 14 16 2 2

Control 8 8 1 1 24

Wireless Transmission 16 4 1 1 18

Sensors 10 22 3 2 10

Power 24 14 2 2 10

Chassis Material 2 2 8 15 2

Design $5,420.00 57 57 56 44 57

Aircraft Design 30 30 36 36 30

Controller Design 27 27 20 8 27

Development $2,760.00 34 34 36 0 34

Aircraft Development 20 20 24 0 14

Controller Development 14 14 12 0 20

Testing $5,040.00 61 61 61 8 61

Component Testing 25 25 25 8 25

Controller Testing 12 12 12 0 12

Aircraft Testing 12 12 12 0 12

Project Testing 12 12 12 0 12

Hours

Table 5

LABET IV PAGE 28

Project Schedule

Table 6

LABET IV PAGE 29

Appendices

Material Properties

Material Cost Density (g/cc)

*Flexural Strength

Elastic Modulus

TS, Ultimate Notes

ABS $11 1.05 70 MPa 2.3 GPa 35 MPa

Fiberglass sheet $77 1.82 455 MPa NA 241 MPa 63% fiber

Wood $10 0.56 57 MPa 12.4 MPa 5.5 MPa Oak

Aluminum $37 2.78 NA 71 MPa 436 MPa 2024 T3

Carbon fiber sheet*

$200- $500 1.60 500 MPa 40 MPa 845 MPa 55% fiber

Plexiglas $21 1.19 99 MPa 2.7 GPa 70.3 MPa

Material Properties (Price is for 0.060" x 24" x 48" sheet) *ASTM-D790 **Prices vary. For carbon fiber, prices are usually specified in price/yard. The average price varies considerably based upon the supplier, weight of the fiber, and orientation of the fiber. Prices were found to be between $30 and $60. Notes on various parameters: Flexural modulus: The highest stress (in any direction) the material can withstand before

failure. Elastic modulus: The ratio of applied stress to strain when the material is subjected to a

tensile stress. A higher value indicates the material a high stress is needed to strain the material a given amount.

TS, Ultimate: The ultimate tensile strength is the highest tensile stress the material can

withstand before failure. References Aluminum price: http://www.onlinemetals.com/merchant.cfm?pid=8051&step=4&showunits=inches&id=915&top_cat=0 ABS, fiberglass sheet, Plexiglas price: www.eplastics.com Carbon fiber sheet price: http://dragonplate.com/ecart/categories.asp?cID=67&p=3

Material Properties were obtained from www.matweb.com

LABET IV PAGE 30

Fan

Fan Specification Table

Fan Voltage vs Thrust

Servo

HiTEC Servos Voltage Torque Speed Weight Size

HSR-5990TG 4.8 to 7.4 30 kg.cm @ 7.4 V 0.12sec/60 degrees at 7.4 68 g (2.39 oz) 40x20x37 mm

HSR-1422CR 4.8 to 6.0 2.8 kg.cm @ 6.0 60 rpm 41.7 g (1.47 oz) 40.6x19.8x36.6 mm

HS-81 4.8 to 6.9 2.6 kg.cm @ 4.8 0.11 sec/60 @ 4.8 16.6 g 29.8x12x29.6

HS-322HD 4.8 to 6.0 3.0 to 3.7 kg.cm 0.19 to 0.15 secs/60 43g 40x20x36.5

HS-475HB 4.8 to 6.0 4.4 to 5.57 kg.cm 0.23 to 0.18/60 40 g 38.8x19.8x36mm

HS-85 BB 4.8 to 6.0 3.0 to 3.5 kg.cm .16 to 0.14 sec @ 60 19.20 g 29x13x30 mm

HS-55 4.8 V 1.1 kg.cm 0.17 @60 7.8g (.27 oz) 22.8x11.6x24mm

Futaba Servos Voltage Torque Speed Weight Size

S3114 4.8 to 6.0 1.5 to 1.7 kg.cm .1 to .09 sec/60 7.8 g (.27 oz) 21.8x11x19.8 mm

S3305 4.8 to 6.0 7.1 to 8.9 kg.cm .25 to .20 sec/60 46.5g (1.64 oz) 40x20x38 mm

S3010 4.8 to 6.0 5.2 to 6.5 kg.cm .20 to .16 sec./60 41 g (1.4 oz) 49.5x20x38mm

S3003 4.8 to 6.0 3.2 to 4.1 kg.cm .23 to .16 sec/60 37.2 g (1.3 oz) 21x20x36 mm

ES350 Nano Servo 4.8 to 6.0 1.2 kg.cm @ 4.8 .13 sec/60 9 g (.32 oz) 22x11x20 mm Servo Selection Table

LABET IV PAGE 31

Gyroscope

IDG-1215 Layout

IDG-1215 Implantation Board

LABET IV PAGE 32

IDG-1215 Implementation Board Pinout

Accelerometer

LIS3LV02DL Accelerometer

LABET IV PAGE 33

Sonar

LV-EZ1 Design and Layout

LABET IV PAGE 34

Software

Software Class Diagram

LABET IV PAGE 35

Aircraft Model

LABET IV PAGE 36

Simulink Aircraft Model

LABET IV PAGE 37

Base Station

LabView User Interface

Base Station Controller