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Autonomous Blimp

Project Design Report

Design Team 02

Jason Banaska

Marcus HorningSagar Patel

Mike Wallen

Faculty Advisor: Dr. Jay Adams

29 November 2011


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Psuedo Code.................................................................................................................. 56

6. Parts List ....................................................................................................................... 60

Table 11 highlights the estimated budget with the corresponding parts for theAutonomous Blimp project. .............................................................................................. 61

5. Project Schedule............................................................................................................ 62 6. Design Team Information ............................................................................................. 64

7. Conclusion and Recommendations ............................................................................... 64

8. References ..................................................................................................................... 66


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List of Figures

Figure 1- Objective Tree ..................................................................................................... 3

Figure 2 - Scaled Drawing of Blimp Envelope ................................................................... 5 Figure 3 - Modeled Gondola Design .................................................................................. 6

Figure 4 - Applied Forces on Free Form Body ................................................................... 7

Figure 5 - Relative Velocity vs. Drag Force ...................................................................... 9 Figure 6 - Relative Velocity vs. Drag Force ..................................................................... 10 Figure 7-Propeller RPM vs. Static Thrust......................................................................... 11

Figure 8 - Simulated Motor Response .............................................................................. 13 Figure 9 - 3D Blimp Coordinates...................................................................................... 13

Figure 10 – Linear Trend Lines ........................................................................................ 17 Figure 11 –Control System ............................................................................................... 19

Figure 12-System Models ................................................................................................. 21 Figure 13 - Step Response of X Translational .................................................................. 22

Figure 14 - Step Response of Compensator ...................................................................... 22 Figure 15 – Step Response of Motor Speeds Due to X-Translational .............................. 23

Figure 16 - Step Response of Z Translational .................................................................. 24 Figure 17 - Step Response of Compensator ...................................................................... 24

Figure 18 - Step Response of Motor Speeds Due to Z-Translational ............................... 25 Figure 19 - Step Response due to Pitch ............................................................................ 26

Figure 20 - Step Response of Compensator ...................................................................... 26 Figure 21 - Step Response of Motor Speeds Due to Pitch ................................................ 27

Figure 22 –Step Response Due to Yaw ............................................................................ 28 Figure 23 - Step Response of Compensator ...................................................................... 28

Figure 24 - Step Response of Motor Speeds Due to Yaw ................................................ 29 Figure 25-Level 2 Hardware Block Diagram ................................................................... 30

Figure 26- LT1963A – Low dropout regulator ................................................................. 33 Figure 27- ADXL345 – 3-axis accelerometer .................................................................. 34

Figure 28-L3G4200D – 3-axis gyroscope ........................................................................ 35 Figure 29-MPL115A1 – Miniature SPI Digital Barometer .............................................. 36

Figure 30-RXM-GPS-SR schematic ................................................................................. 36 Figure 31-The LV-MaxSonar-EZ4internal connections [10]. .......................................... 37

Figure 32-Xbee Pro Pin Layout ........................................................................................ 38 Figure 33-PIC24FJ256GB108 recommended connections. ............................................. 39

Figure 34- Voltage divider to monitor battery voltage ..................................................... 40 Figure 35- Release Valve System ..................................................................................... 41

Figure 36 – Hardware Level 1 Block Diagram ................................................................. 42 Figure 37 - Software Level 0 Block Diagram ................................................................... 45

Figure 38 - Software Level 1 Block Diagram ................................................................... 46 Figure 39 - Software Level 2 Block Diagram ................................................................... 47

Figure 40 - Software Level 2 Functional Requirements ................................................... 48 Figure 41 - Xbox 360 Controller Configuration ............................................................... 50

Figure 42- Xbox 360 Analog Stick Sensitivity ................................................................. 51 Figure 43- Ground System Class Diagram ....................................................................... 52

Figure 44- Blimp Controller Execution Loop Sequence Diagram ................................... 54 Figure 45 - Transmission byte sequence from ground system to blimp ........................... 54


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Figure 46 - PWM Duty Cycle Motor Control Relationship ............................................. 56


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List of Tables

Table 1- Design Requirement Specification ....................................................................... 4 Table 2 - Parts List with Estimated Weights ...................................................................... 8

Table 3-Motor Properties .................................................................................................. 12 Table 4-Motor Properties .................................................................................................. 12

Table 5 - Damping Coefficients ........................................................................................ 18 Table 6- Level 2 Hardware Functional Requirements ...................................................... 30

Table 7- List of IO Pins .................................................................................................... 39 Table 8 – Hardware Level 1 Functional Requirements .................................................... 43

Table 9 - Software Level 0 Functional Requirements ...................................................... 45 Table 10 - Software Level 1 Functional Requirements .................................................... 46

Table 11-Parts List ............................................................................................................ 60 Table 12-Estimated Budget............................................................................................... 61


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Abstract

Unmanned Aerial Vehicles (UAVs) operate under remote or autonomous control

and are used for surveillance applications, usually when human interaction is not

possible. A blimp UAV with feedback control is of special interest because of theirability for long flight duration and low power operation. The objective of this project isto design and construct a remote controlled aerial surveillance blimp that will exhibit

self-stabilization capabilities and safety control at a low cost budget. A motor systemwith sensor feedback will need to be constructed in order to create autonomous flight

stability. Along with continuous surveillance video feedback the blimp shall also provide transmitted data including: craft coordinates, weather measurements, battery

power status, and indication of oncoming obstacles. The craft will have a predefinedenvelope and the control compensator will be designed through research findings,

computer simulations, and experimental testing. A model of the control system based onthe flight dynamics of the air-craft is analyzed to design a controller for the system. The

control system features a four motor system that can exhibit vertical and horizontaltranslational control, as well as pitch and yaw rotational control. This report summarizes

the preliminary control, communication design, and additional user friendly features ofthe remote control blimp.

Key Features:

• Accurate and stable flight• Intuitive remote control• Feedback of live video and critical sensor data• Supplementary autonomous functions

1. Problem Statement

Need

Aerial video surveillance can be used in many different applications. For instance,

aerial surveillance can aid rescue workers to find a missing person or be used to gathermilitary intelligence. A live video feed can also be useful in other emergency situations

such as riots, fires, earthquakes, and tsunamis. Chemical companies have expressedinterest in using a UAV craft to monitor corrosion of pipes in places where it would be

difficult for human interaction. Companies can use aerial surveillance to put a set of eyeswhere it would be dangerous to send employees. Other companies could use aerial

surveillance to monitor habitats and growth of areas and landscapes. There is a need to provide a cost effective way to achieve aerial surveillance for informational purposes.

Objective

The goal of this project is to create an easy-to-control, self-stabilizing, airship thatcan provide live aerial video feedback to the user. In addition, it will be able to provide


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the location, speed, and battery level voltage of the airship. The craft will be able to beflown remotely with an X-Box controller. It will also be able to perform some

autonomous functions such as; self-stabilizing when the user releases control of theremote or communication is lost, stopping movement in the z-direction when the altitude

limit of 122m is reached, and stopping further movement when obstacles are detected.

For surveillance, a camera will be attached to the craft and it will be capable of relayingreal-time video back to the user, thus allowing the craft to be flown without a direct lineof sight. Along with this video, the battery level, weather information, and other sensor

data previously mentioned will be displayed on a self-made graphical user interface presented on a computer screen.

Background

Current designs for RC blimps typically have a large, non-rigid helium-filled hull

(balloon) with two to three rotatable propellers attached to provide flight direction andspeed. Below the hull, there is typically a gondola which houses the communication

transceiver, battery, and has the motors attached to the outside. Either combustionengines or electric motors are typically used. Despite electric systems usually being

heavier, it is the choice more commonly used to allow for very precise throttling andmaneuverability. Tail surfaces and rudders are designed and placed at the rear of the hull

with the intention of providing effective control of the direction of the blimp.The primary concern with using a blimp is that the volume required to lift a rather

large payload which potentially includes the motors and motor controllers, severalsensors, a microcontroller, a battery supply, and a camera would be quite large. Helium

is typically used for blimps, and can lift approximately 1kg/m3 (0.064lb/ft

3) which is

based on the differences in densities of the air and helium. In order to have a manageable

size, the payload would need to be minimized as much as possible.


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Objective Tree

Below is the objective tree for the project, which represents the marketing requirementorganized into a hierarchy of needs.

Surveillance Aircraft

Easy to Use Stable and Accurate Flight Safety

Indoor/Outdoor Use

Intuitive, Responsive User

Remote Control

Light Weight

Avoid Obstacles

Self-stabilizing in All

Directions

Direction and Position

Awareness

Displays Video and OtherData Back to User

Self Stabilize When Idle

Inform User When Battery

Level is Critical

Safe to Use and Fly Around

People

Figure 1- Objective Tree


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2. Design Requirements Specification

Below is the design requirements specification for the blimp system.

Table 1- Design Requirement Specification

MarketingRequirements

Engineering Requirements Justification

6 The airship should have an average flight duration

of twenty minutes.

Based on the 5000mAh rating on the

battery and the average current draw.

6 Display warning message on graphical user

interface (GUI) on computer when battery voltage

level reaches the critically low voltage level.

This feature is intended for craft and

personnel safety. Critically low

voltage is determined from battery

reading, dependent on the number of

cells and battery type.

7 The gondola, sensors, motors, and additional

hardware should be detachable from the blimp

envelope in less than 5 minutes.

The blimp must be transportable for

indoor and outdoor use. The envelope

will also be used independently by a

second party.

8 The airship must make one full rotation in the yaw

direction in under 60 seconds.

This value is determined by user

specifications.

1,2,9 The maximum allowable drift during autonomous

flight in any direction is 1 m when wind gusts are

below 3 m/s.

The amount drift is based on the

control system compensation.

3 The user control should allow the operator to

control the pitch and yaw rotational directions, as

well as the x and z translational directions. The

analog joystick on the remote will control the

rotational directions and the buttons will control the

translational movements of the craft.

The user needs to be able to have full

control of the craft's flight trajectory,

with ease of use.

5 The craft must come to a stop and warn the user via

the GUI when an obstacle is within 1m and lies in

the direction of the flight path.

This value is based on the maximum

drift of the airship and the value of the

ultrasonic range finder.

8 The airship’s speed in the vertical direction must be

able to achieve 0.5 m/s in less than 10 seconds.

Also, the airship must obtain a speed of 1.8 m/s in

the horizontal direction in less than 6 seconds.

This value is user specified and is

dependent on the thrust that the

motors can produce.

10 The airship should not exceed a maximum altitude

of 122 m above ground level and must warn the

user when the craft is approaching this position.

This is a model aircraft operating

standard in the Advisory Circular 91-

57.

4 The device must transmit 800 meters line of sight

the craft’s battery voltage level, position, altitude,aircraft speed, distance to obstacles ,and the air

pressure and temperature of the atmosphere.

The maximum range of transmission

of the XBee Pro transceiver is 1.609km.

4 The accuracy of the transmitted data must be as

follows:

-Temperature within 1ºC

-Air pressure within 1kPa

-Battery voltage within 5% of actual voltage

-Speed within 5% of actual speed

The accuracy of the data is based on

the constraints of the sensors quality.


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-GPS position within 5 meters

Marketing Requirements:

1. The craft must be stable in flight in all directions.2. The craft must self stabilize in the absence of user control or when communication is lost.3. The craft must be intuitive to control via the remote control.4. The display unit must provide the user with the craft’s coordinates, altitude, video feed, and battery

voltage.

5. The craft must avoid contact with obstacles during flight.6. The craft must have battery life that will sustain long periods of flight and the user shall be warned

when the battery power is critically low.

7. The craft must be easy to assemble to provide ease of use and transportation.8. The craft must respond readily to all user commands.9. The craft must be able to fly outdoors.10. The craft must comply with Advisory Circular (AC) 91-57 for Model Aircraft Operating Standards.

3. Accepted Technical Design

!"#$%&'#%( *"+',&(MW,MH)

At this point in time, the blimp that is being considered for the project is owned

by The University of Akron’s Department of Biology. A scaled drafting of the blimp, provided by Southern Balloon Works, is shown in Figure 2.

Figure 2 - Scaled Drawing of Blimp Envelope

The design of the blimp’s gondola is an important factor in how the blimp will

operate. The gondola design must be light in weight and yet still be able to firmly houseall of the motors. The current design schematic shown in Figure 3 features an easily


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adjustable gondola design. The material being used for the gondola consists of PVC pipeand a thin wood board or sheet of plastic that can securely hold all of the electrical parts.

The length of the board will be approximately 2 meters, or long enough to allow thevertical motors to be effective for controlling the pitch of the craft. The PVC pipe allows

for the gondola frame to be customizable to ensure that the weight requirements of the

blimp are satisfied. The initial dimensions used for the gondola frame is 1 meters long by0.3 meters wide by 0.3 meters tall, and the weight of the frame was measured to beapproximately 1.10 kilograms. Additional frame pieces can be added if it is determined

that more weight is needed for the payload capacity. If the frame is determined to be tooheavy, an additional alternative may be CPVC pipe, which is lighter in weight. The

frame was design in such a way that it can easily tied or inserted through several metalloops at the center of the blimp. In addition to the motors, the gondola will also house the

inertial measurement sensors, the XBEE receiver, battery packs, and wireless camera,which are not shown in Figure 3.

Figure 3 - Modeled Gondola Design

By examining the external and applied forces on the airship, three parameters ofthe mechanical design of the airship can be determined. These include the volume of the

envelope, the resulting weight of the payload, and thrust required for satisfactoryacceleration. The desired accelerations will be chosen to satisfy the respective design

requirements regarding the response of the airship. Once the accelerations and requiredthrust are determined, the motor can be chosen based on its electrical performance. A

free-body diagram of the forces that act on the blimp are depicted in Figure 4 where T

represents the magnitude of the thrust. The blimp is assumed to be flying in the -!

direction. Also, the center of mass and center of buoyancy are presumed to both belocated at the same point.


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In order to reduce a non-linearity in the control system, the airship will be

neutrally buoyant. Therefore, by examining the forces in the ! direction it is evident that

the force of buoyancy must be equal to the weight of the blimp so that acceleration doesnot occur in that direction. The force of buoyancy is an effect of the density of the lighter-

than-air (LTA) gas used being less than that of air. Therefore, the magnitude force isdependent of the volume of the envelope and density of gas used. The most commonly

used LTA gas for blimps and airships is helium, which has a lift capacity of 1kg/m3. The

force due to the effect of gravity, or the weight of the blimp, is dependent on the

combination of the masses of the envelope and the on-board equipment.

The volume and weight of the blimp is 8.5!! (300 cubic feet) and 3.86kg (8.5lbs) respectively. In order to determine if this envelope will be suitable for the blimp

design, it is necessary to hypothesize a payload based on the parts needed to both operatethe blimp and also meet the marketing requirements. The volume of the blimp must be

large enough such that the buoyant force exceeds or is equal to the total weight of thesystem. These forces will later be equalized by either adding mass to the system or the

increasing the density of the containing gas (i.e. an air/helium combination will be used).A list of potential parts is summarized in Table 2 with estimated system mass.

!!"#$= - D!

!

!!= !!!!

!! =

!! !

!!= !!!!

!!"#$=

!!"#$ !

W= -mg !

Figure 4 - Applied Forces on Free Form Body


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Table 2 - Parts List with Estimated Weights

Part Estimated Mass (g)

Ultrasonic Sensor (2) 13

Gyroscope 1

Barometer 1

GPS Chip 3XBee Receiver 3

Camera (Not required) 21

Back-up Battery 15

Accelerometer 1

Microcontroller 3

Motor Electronic Speed

Controllers(4)

80 (20 g each)

Motors (4) 440 (110 g each)

Propellers (4) 32 (8 g each)

Battery 332 g

Gondola and attachment

materials

1250

Electronic Release Valve 45

Envelope including fins (4) 3629

Mass of Helium 1517

PCB (10"x4") 50

Additional Hardware/Wire

(Resistors, Caps, etc)

40

Total Estimated Mass 7476

with 10% added 8224

After reviewing the mass, it is determined that the volume of the blimp is indeed largeenough to produce lift. The weight of the system of 8.22kg was less than the lifting

capacity of 8.5kg. However, a concern we have considered is that the shape of theenvelope was designed for advertising and is not desirable for flying. A better shape for

flying is generally a more slender body such that the air drag is reduced. More air dragwill pose a challenge in the control aspect because a nonlinearity will be introduced and it

will not be modeled in a linear system.

By examining the forces shown above in the Figure 4 the thrust required in !

direction that results in a desired acceleration, !!can be found using Newton’s second

law, and is depicted as

!!"#$%! ! !!"#$ !!! ! An acceleration of 0.4 m/s

2 was chosen such that the requirement stating that the airship

must obtain a horizontal speed of 1.8 m/s in less than 6 seconds will safely be satisfied.The drag of the blimp is determined by force equation for drag given by

(1)


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!!"#$ !!

!! ! ! ! ! ! ! !

!!

In equation 2, C is a dimensionless drag coefficient that is shape dependent, ! is

the fluid density of air, S is the cross-sectional area, and v is the velocity of the blimp. Itis assumed the nose of the blimp flies forward, directly into the drag. According to Dr.

Stavros Androulakakis of Lockheed Martin, a drag coefficient of 0.1 is appropriate for

the blimp moving in the ! direction. Likewise, a drag coefficient of 1.2 is appropriate for

the blimp moving in the ! direction [2]. These coefficients are dependent on the shape of

the blimp. The fluid density of air taken at an ideal ambient temperature of 25oC at the

standard atmospheric pressure of 101.325 kPa is 1.1644 kg/m3. The reference area from

the front of the blimp is defined as the area of the circle, ! r 2. Using the values described

above, the drag force is shown in Figure 5 as the velocity of the blimp, relative to the

velocity of air, is varied.

By inspection of the graph, the drag force at a relative velocity of 4.8 m/s is 4.1

Newtons. That relative velocity was chosen because it corresponds to the blimp travelingat maximum speed into a maximum wind speed. Since the desired acceleration and dragforce are now determined, the force of thrust required for a 8.2 kg system as determined

by Equation 2 is 7.38 N. Since all four motors are identical the thrust required to satisfythe requirements in the vertical direction will not exceed 7.38 provided that the drag force

is low enough. The drag force for a relative velocity is shown in Figure 6.

"

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'

" # $ % & ' (

! " # $ & ' " ( ) * + ,

-).#/0) 1).'(234 *567,

-).#/0) 1).'(234 078 !"#$ &'"()

)*+,*-#

(2)

Figure 5 - Relative Velocity vs. Drag Force


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By inspection of the graph, the drag force at a relative velocity of 1 m/s is 5

Newtons. Although this value is larger than that of the blimp traveling in the i-direction,the acceleration will be low enough such that the thrust required will be lower than 7.38

Newton. Therefore, the propellers and the resulting motors will be chosen based on 7.38 Newton.

The thrust produced is a property of the propellers used. However, these must bechosen in conjunction with the motors so that the torque developed by the loading to the

propeller will not exceed the stall torque. In addition, the motor must be able to run at ahigh enough rpm such that the necessary thrust is produced. Also, the current draw must

be low enough such that the requirement regarding flight duration is satisfied. Althoughthe thrust produced by a propeller when in motion, known as dynamic thrust, varies from

that produced under static conditions, dynamic thrust is difficult to calculate. However,since the airship will be flying at a low velocity it is presumed to be flying under static

thrust. The static thrust is a function of the propeller’s rpm, diameter, CF value, and thedensity of air and is given as

!!"#$%! ! 9.459!!"!!"!!!!!!!"!.The CF, or coefficient of lift, is a dimensionless value that relates the lift force with the

dynamic pressure and reference area and varies with different propellers. A double-

bladed propeller with a 9-inch diameter and a 6-inch pitch was chosen. The static thrustdeveloped as a function of rpm is shown for that specific propeller in Figure 7.

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Figure 7-Propeller RPM vs. Static Thrust

By inspection of the graph, the thrust of the propeller is proportional to the square of the

rpm. For this particular propeller the relationship between static thrust and RPM is

!!"#$%! ! !!!"# ! !"!!!!.As mentioned previously it is also important that the propeller’s torque does not exceedthe stall torque of the motor. The torque of the motor is a function of the power produced

by the propeller and the rpm of the propeller. This relationship is given as

! !!

!

.

Whereas the power developed by the propeller is defined as

!!"#! ! !! !!! !.

Both P c and p f are coefficients that are specific to the propeller. The P c coefficient is the

power constant of the propeller and p f is the power factor, which is typically equivalent tothree.

Also, mentioned previously was the importance of monitoring the current drawneeded to produce thrust. This is not only to ensure that the current does not exceed the

maximum rating of the motor, but also to design the propeller/motor combination so thatthe battery life satisfies the design requirement. There are two ways to calculate the

current. The first requires knowledge of the motor torque constant, k t , and the torque produce. These properties are related by

! !!!

!

.

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'

#"

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$"

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" $""" &""" (""" /""" #"""" #$""" #&"""

= > " ? 7 3 @ 2 : + ) 9 3 '

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A"'C)..)" -AB 078 D3#/( =>"?73

)*+,*-#

(4)

(5)

(6)

(7)


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The second method requires knowledge of the efficiency of the motor, the operating

voltage, and the delivered propeller power. These properties are related by

! !!!"#!

!".

A computer-aided simulation tool designed by Louis Fourdan of Maxx Products

International LLC was used to choose the appropriate motor and propeller. The finalselection of the motor had the following properties listed in Table 3. The properties of the

selected propeller are shown in Table 4.

Table 3-Motor Properties

0121+ )3**4 516-276289: ;#" ?

07@,ABA C63B2 D7227E* $'" D

C62*+67F L

Table 4-Motor Properties

P,7A*2*+ ; ,6GI*-

=,2GI ( ,6GI*- NI+B-2 51*QQ,G,*62 !!!"#! !"!! Number of blades 2

Power Constant, P c 0.822

Power Factor, p 3

The simulation for the selected motor and attached propeller is shown in Figure 8.The dot on the current vs. efficiency chart represents the operating state of the motor at

11V (maximum voltage input). With back-emf taken in to account, the delivered thrust is855 gram-force (8.39 N) at 8371 rpm. This value of thrust for one motor will result in an

acceleration that will satisfy the design requirements. Additionally, the torque of themotor is 0.135Nm when the maximum current is 13.73A. The input power is 150W,

which is well below the rated input power.

(8)


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Figure 8 - Simulated Motor Response

-../0'&%1"+ %&0 *'/"#1'.&+(JB)

The coordinates and directions used in remainder of this report when referencing

the blimp is shown in Figure 9. The directions shown by the vectors x, y, and z arereferenced to the frame of the blimp. Therefore, as the blimp rotates, so do the unit

vectors r, u, and v. On the other hand, the rotations have an earth frame reference.

Figure 9 - 3D Blimp Coordinates


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2"3/"+"&1%1'.& .4 1$" -.&1/.( 56+1"7(JB,MH)

Controlling the autonomous airship requires knowledge of all of the forces that appear on

it. The airship has six degrees of freedom that accelerations can occur (!,!, !,!!,!!,!!).

The control model of plant for each of the subsystems can be obtained by the differentialequations that represent the dynamics of the system. The six differential equationsrepresenting the six degrees of freedom are obtained by equating Newton’s second

law[1,14] given by ! !!" in each translation and rotation direction. In the rotational

directions, Newton’s second law suggests that ! ! !" where ! is a moment of inertia

about the mass center,! is a moment, and ! is an angular acceleration.

By analyzing each direction separately the differential equations can be obtained.In addition, some insights can be developed concerning the general motion of the system.

The transfer functions will also be produced from the differential equations.

X-Translation

Movement in the ! direction is defined as the airship moving directly horizontallyforward. The two motors that affect this movement are M1 and M2. Creating a dynamic

equation for the !-translation arrives at!! ! !!!! !!! !!!!.Where m is the massof the airship, b is a damping coefficient caused by wind resistance, while M1 and M2 are

the thrust (force) produced by each of the motors. However, if motors 1 and 2 are only powered, then a pitch is created around the center of buoyancy. To compensate for this

pitch, motors 3 and 4 are needed to compensate for the added pitch. The transfer functionwith the output to the system being the velocity of the blimp and the input being the

motor thrust produce only in the ! direction is

!!!!!

!!!!

!

!

!!

!

!!"

.

Y-Translation

Movement in the ! direction is not directly controllable from the motors located

on the airship. A dynamic equation for the forces in the! direction is!! ! !!!.Therefore, if there is a gust of wind that pushes the airship in the ! directionadjustments

in the yaw and !-translation directions are needed to control the blimp back to its original

position. Since there is user input in this direction the transfer function has no value.

Z-Translation

The movement in the ! direction is controlled by motors 3 and 4.Since these

motors will be placed at an equal distance from the center of mass no net moment will be

applied to the system. An equation for the forces in the ! direction is!! !!!!!

!!! !!!!.The transfer function with the output of the system being the velocity of the

blimp in the ! direction and the input being the thrust produced by the combination ofmotor 3 and 4 is given by

!!!!!

!!!!!

!

!!!!!"

.

(9)

(10)


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Pitch !

Pitch is very important to be able to control, and the system’s setup has fourmotors that will alter the pitch. Each motor will cause an angular acceleration in the pitch

since there is a moment arm directed from the position of the motor to the center of mass.

The differential equation for the pitch is given as !! ! !!! !!! !! !!! !

!!"!!!!!

!!!!. The transfer function with the input to the system being the moment

produced that causes a roll and the output being the pitch angle is

!!!!

!!!!!

!

!!!!!!"

.

Roll ! Roll is the acceleration that occurs around the !-axis. There are no motors on the

airships that can control the roll of the system. Also, there will be no moment resulting

from the thrust produced by the motors that will affect yaw. The differential equation for

roll is described by !! ! !!. Since there is no the motor that control this direction onceagain the transfer function will have no value.

Yaw ! Yaw is rotation about the !-axis. Direct control the yaw of the craft is influenced

by motors 1 and 2. The motion is represented by the dynamic equation !! ! !"!!!"!! ! !!! !!!!. However, if motors 1 and 2 are controlled to produce moments withthe same magnitude but opposite direction then no net yaw is created and the craft only

moves in the !-direction. Motors 1 and 2 must be spinning at different speeds to create achange in yaw. While creating a change in yaw, once again, the pitch level also needs to

be adjusted because it gets affected when adjusting the yaw. The transfer function with

the angular velocity being the output and the moment produced in the yaw direction asthe input is

!!!!

!!!!!

!

!!!!! !"

.

Since all the equations of motion are now obtained, they are represented in matrix form

given as

(11)

(12)


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of the location of the center of mass. Nevertheless, damping coefficients of 1 werehypothesized as a conservative value in the pitch and yaw-direction. The damping was

neglected in the roll-direction. These values were chosen because a straight-line, uniformwind would produce a minimal moment.

The moments of inertia were obtained by superposition of the moments of inertia

calculated for an ellipsoid and a thick plate. In addition, the parallel axis theorem wasused to obtain the moments of inertia at an estimated location determined to be the masscenter. This location was closer to the front and the base of the envelope. The geometric

parameters of the

Figure 10 – Linear Trend Lines

With A=0.95m, B=0.95, C=0.95 m, D=0.25m,W=0.25m ,H=0.15 m,

!!"#

! !!!"#$ !!"#$%&'( !"#$%&!! !"# !!"#$=4kg, the moments of inertia can becalculated by

!!!

! !!!"#

!!!!

!

!!! !

!!"#$ !

!!!

!

!"!!!"#$!!!!

!!,

!!! ! !!!"#!!!!

!

!!!

!"#!!"!!!!! !

!!"#$ !

!!!

!

!"!, and

!!!

! !!!"#

!!!!

!

!!!

!"#!!"!!!!! !

!!"#$ !

!!!

!

!"!.

The values !"!and !"!represent the distances from the originally center of mass to theanticipated center of mass. However, they were neglected. The calculated values for the

damping coefficients and moments of inertia are shown in Table 5.

(13)

(14)

(15)


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18

Table 5 - Damping Coefficients

P7A3,6E 51*QQ,G,*62-

7 ".R&

S '

G '

4 # * "

Q #

01A*62- 1Q ,6*+2,7

T3 (.(' +74>-*G

T+ $.;R +74>-*G

TU7V '.(( +74>-*G

The values listed in Table 5 were calculated based on theory. However, the valuesof the damping coefficients and moments of inertia will obtain experimentally to obtain a

more accurate model of the system. This procedure requires a method of obtaining a stepresponse in each direction. In addition, the translational/rotational distance must be

sensed.Each of the six system models will be obtained separately. A step in the respective

direction will be inputted into the system by powering the appropriate motors. Thedistance (angle for rotational directions) will be plotted on the oscilloscope in terms of

the voltage. The transfer function of the system will match the prototypical second orderequation given as

!!!

!!!!"!!!!!!

! .

The natural frequency, !!

, and damping ratio, !! can be obtained by calculating the timeconstant, ", and damped frequency, !!, from the step response. They can then becalculated using

! !!

!!!

and

!! !

!!

!!!! .

The time constant of the model is equivalent to the time it takes to reach 67% of the final

value. The damped frequency is the inverse of the time between consecutive peaks. Once! and !! are known, the coefficients of the prototypical equation can be related to the

system model to determine the damping coefficients and moments of inertia (forrotational directions only).

(16)

(17)

(18)


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19

-.&1/.( 56+1"7 873("7"&1%1'.&(MH)

In the previous section it was determined that only four directions (!,!! yaw, and

pitch) can be controlled. The implementation of the control system is illustrated in Figure11.

Ux

Uyaw

Desired

Velocity in

x-direction

Desired Yaw

Velocity

Transfor

mation

M1

M3M2

M4

Up

Z

Controller

Uz

Desired

Velocity in

z-direction

Aircraft

DynamicsYaw

Controller

Pitch

Controller

X

Controller

Desired Pitch Angle

x

pitch

yaw

z

-

-

-

-

Aircraft

System

Dynamics

Figure 11 –Control System

There are four inputs and four outputs of the system. The goal is to be able to control thetranslation velocities in the x and z directions, the rotational velocity in the yaw direction,

and the pitch angle. The designed compensators, which will be discussed in more detaillater, will multiply the respective error to obtain Ux, Up, Uyaw, and Uz. The actual

velocity and angle values will be obtained by the combination of accelerometer,

gyroscope, and GPS sensor data. The values of Ux, Up, Uyaw, and Uz represent thethrust/moment required in the respective direction. The required thrust/moment isdependent on the four motors and is represented by the coupled set of equations given as

!!

!!

!!

!!

!

! ! ! !

! ! ! !

!!! !!

!!!!! !!!

!!!!!!

! ! !

!!

!!

!!

!"

% (19)


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20

As mentioned previously M1,M2,M3, and M4 represent the thrust produced bymotors 1 through 4 respectively. Also, dz’, dx’, and dy’ are the moment arms depicted in

Figure 9 on Page 13. The coefficient ! represent the effect of the body of the blimp’s

tendency to rotate as a result of the propeller’s inertia. However, this effect was neglecteddue to the relatively large mass of the envelope. The motor control algorithm is

implemented to determine the thrust and therefore the resulting speed each motor must produce. This is done by solving for M1, M2, M3, and M4 in Equation 19 in terms of the

measureable values of Ux, Uz, Up, Uyaw. These result in the four motor thrust equationsgiven as

M1=(Uyaw + Ux*dy’)/(2*dy’),

M2=-(Uyaw - Ux*dy’)/(2*dy’),

M3=(Uz*dx’ - Upitch + Ux*dz’)/(2*dx’), and

M4=(Upitch + Uz*dx’ - Ux*dz’)/(2*dx’).

(20)

(21)

(22)

(23)


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21

The motor rpm is related to the thrust by Equation 4 on page 11. However, motors twoare four were chosen to have counter-pitched propellers to reduce the effects of motors

causing rotation of the body.

-.73"&+%1./ *"+',&

The four compensators are designed for increased stability of the system, zerosteady-state error, minimum overshoot, and a settling time that satisfies the design

requirements regarding the motion of the system. The four compensators were designedseparately. The system models are all illustrated by Figure 12. Please refer to pages 14-

15 for the models of the plant. The compensators were all designed with the gain of thefeedback sensors equal to unity. The system was transformed from the s-domain to the z-

domain using a zeroth-order hold and a sampling time of 20ms. Also, the output of thecompensators needed to be monitored to ensure that value does not exceed a thrust that is

not obtainable.

Yaw

ModelYaw

Controller

UyawDesired angular velocity

in yaw direction

Z

ModelZ

Controller

UzDesired velocity in

z direction

Pitch

ModelPitch

Controller

UpitchDesired pitch angle

X ModelX

Controller

UxDesired velocity in

x-direction

Figure 12-System Models

X-Translational:

The velocity of the system is in inherently stable. However, due to the effect ofdamping, a PI controller is necessary to obtain zero steady-state error and reduce the


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22

settling time. Please refer to the appendix for the MatLab code used to design thecompensators. The resulting transfer function for the compensator in the x-direction is

! ! !!!!!!!!!"#!

!!! .

The step response of the output of system to 1.8 m/s is shown in Figure 12. The stepresponse of the output of the compensator is illustrated in Figure 13, where the amplitude

represents the thrust required in the respective direction. These step responses correspondto the motor speeds illustrated by Figure 14.

Figure 13 - Step Response of X Translational

Figure 14 - Step Response of Compensator

0 1 2 3 4 5 6 7 8 90

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2Step Response

Time (sec)

A m p l i t

u d e

0 1 2 3 4 5 6 7 8 9 10

1

2

3

4

5

6

7

8

9Step Response

Time (sec)

A m p l i t u d e

(24)


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23

Figure 15 – Step Response of Motor Speeds Due to X-Translational

Z-Translational: Similar to the x-direction, the velocity of the blimp in the z-direction is stable but

a PI controller is needed to reduce the steady-state error and settling time of the system.The gain of each compensator was chosen such that the output of the compensator was

less than 40% of the maximum thrust/moment that can be produced in the respectivedirection. This was done to account for the instance when two or more directions were

controlled simultaneously. The resulting compensator transfer function in the z-directionis

! ! !!"!!!!!!"#!

!!! .

The step response of the output of the system for a velocity of 0.5 m/s in the z-direction isshown in Figure 15. Figure 16 shows the step response of the output of the compensator,

where the amplitude represents the thrust required in the z-direction. Once again, themotor rpm’s to obtain the step response are shown in Figure 17.

0 1 2 3 4 5 6 7 8 9 100

5000

10000Motor rpms for Desired Step Response

0 1 2 3 4 5 6 7 8 9 10-10000

-5000

0

M o t o r r p m

0 1 2 3 4 5 6 7 8 9 100

5000

0 1 2 3 4 5 6 7 8 9 100

5000

Time, in seconds

(25)


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24

Figure 16 - Step Response of Z Translational


0 2 4 6 8 10 12 140

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Step Response

Time (sec)

A m p l i t u d e

0 1 2 3 4 5 61.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6Step Response

Time (sec)

A m p l i t u d e


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Figure 18 - Step Response of Motor Speeds Due to Z-Translational

Pitch:The pitch of the system is not inherently stable. Therefore, a PD controller was

designed to not only make the system stable, but also to reduce the settling time. No

compensation was needed to reduce the steady-state value because the plant already had a pole at the origin. The transfer function of the compensator in the pitch direction is givenas

! ! !!"!!!!!!!"#!

!!! .

The step response of the output of the system for a desired angle of 0.4 radians is shown

in Figure 18. The step response of the output of the compensator is shown in Figure 19where the magnitude represents the required moment. The required rpm of motors for the

desired input is shown in Figure 20.

0 1 2 3 4 5 6-1

01

Motor rpms for Desired Step Response

0 1 2 3 4 5 6-1

01

M o t o r r p m

0 1 2 3 4 5 63000

40005000

0 1 2 3 4 5 6-5000

-4000-3000

Time, in seconds

(26)


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26

Figure 19 - Step Response due to Pitch


0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

2

4

6

8

10

12

14Step Response

Time (sec)

A m p l i t u d e

0 10 20 30 40 50 600

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45Step Response

Time (sec)

A m p l i t u d e


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Figure 21 - Step Response of Motor Speeds Due to Pitch

Yaw:

The velocity of the blimp in the yaw-direction is also inherently stable.Depending on the magnitude of the damping coefficient a compensator may be require to

reduce the steady state error. Since the magnitude of the damping coefficient of the realsystem likely cannot be neglected, a PI compensator will be needed. The transfer function

of the compensator in the yaw direction is given as

! ! !!"!!!!!!!"!

!!! .

The step response of the output of the system for a desired angular velocity of 0.4 radiansis shown in Figure 21. The step response of the output of the compensator is shown in

Figure 22 where the magnitude represents the required moment. The required rpm of themotors for the desired input is shown in Figure 23.

0 5 10 15 20 25-1

01


0 5 10 15 20 25-1

01

M o t o r r p m

0 5 10 15 20 25

-4000-2000

0

0 5 10 15 20 25

-4000-20000

Time, in seconds

(27)


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Figure 22 –Step Response Due to Yaw


0 0.5 1 1.5 2 2.50

0.5

1

1.5

2

2.5Step Response

Time (sec)

A m p l i t u d e

0 5 10 150

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Step Response

Time (sec)

A m p l i t u d e


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Figure 24 - Step Response of Motor Speeds Due to Yaw

Block Diagrams and Theory of Operation (JB)

Level 2 Hardware

The hardware’s operation primarily focuses sending the desired motor speeds to themotor controllers by reading sensor inputs. The microcontroller is the heart of thecircuitry and communicates with all of the sensors to provide the desired motor controller

speeds. The sensors include a gyroscope, accelerometer, GPS, barometer, and ultrasonicsensors. The low power circuitry gets all of its power from a primary battery that a low-

dropout regulator converts to provide the correct voltage to each component. The higher

power circuitry, such as the motors and motor controllers, get their power from a separate battery with no low-dropout regulator. Data is generated and transmitting wirelesslythrough XBee Pro and is displayed on a monitor for the user.

0 20 40 60 80 100 1200

20004000


0 20 40 60 80 100 1200

20004000

M o t o r r p m

0 20 40 60 80 100 120-1

01

0 20 40 60 80 100 120-1

01

Time, in seconds


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30

MicroController

Low-Dropout

Regulator

Battery 1

Xbee Pro PCXbox 360

Controller

Motor 1

Motor

Controller

1

Motor 2

Motor

Controller

2

Motor 3

Motor

Controller

3

Battery

Voltage %

Desired SpeedM1

Desired Speed

M3

Desired SpeedM2

Thrust

Thrust

Thrust

Vin

Xbee Pro

Battery

Monitor

Desired

x-translation

Desired Yaw

Desired Pitch

Monitor

Xbee

Adaptor

Transmitter

Televison

Camera

Receiver

Accelero

-meter

Gyroscope

Barometer

Ultrasonic

Proximity

Sensors

Camera

Motor 4

Motor

Controller

4

Desired SpeedM4

Thrust

Desired

z-translation

GPS

Sensor

Battery 2

BackupGPS

Battery

Figure 25-Level 2 Hardware Block Diagram

Table 6- Level 2 Hardware Functional Requirements

Module Low-Dropout Regulator (LT1963A)

Inputs Power In: 11.1V Battery input

Outputs Power Out: 3.3V Output to Microcontroller, Ultrasonic Sensors,Barometer, Accelerometer, Gyroscope, Xbee Pro, and GPS

Sensor.Functionality Provide regulated voltage and current to several inputs of sensors and the

microcontroller.

Module Microcontroller (PIC24FJ256GB106)

Inputs Power In: 3.3V In from LDO

Ultrasonic Sensor Data: Distance (m) of objectsXbee Input: Desired positioning of system


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Barometer Input Data: Air temperature measurement

GPS Sensor Data: Altitude and coordinates of blimpAccelerometer Data: Actual translational measurements

Gyroscope Data: Actual rotational measurementsBattery Monitor: Battery voltage level for critical level

Outputs Desired Speeds: Send desired speeds to motor controllers.Xbee Output: Collected data needing to be sent to ground

Functionality Receives, communicates, and processes all data from sensors. Developsdesired motor speeds and also sends desired data to Xbee to be sent to the

ground.

Module Xbee Pro

Inputs Data In: Data to be transmitted wirelessly

Power In: 3.3V In from LDO

Outputs Data Out: Data sent out wirelessly

Functionality Transmits data wirelessly from Xbee transmitter to Xbee receiver.

Module Xbox 360 Controller

Inputs Desired Positioning: Desired x-translation, z-translation, pitch,

and yawOutputs Control to PC: Send signals to the PC

Functionality Desired inputs are directed using the Xbox 360 controller and sent to the

PC to be analyzed.

Module Camera Receiver

Inputs Images: Images sent wirelessly from camera on blimp to receiveron ground

Outputs RCA output: RCA output to connects to a television.

Functionality Images are taken by the camera and sent to the camera receiver and then

displayed on a television.

Module Battery Monitor

Inputs Power In: 0V-11.1V Battery input

Outputs Power Out: 0V-5V to microcontroller.

Functionality Uses a voltage divider to send 0-11.1V from battery to 0V-5V tomicrocontroller so it can sense when the battery is getting to a critical

level.

Module Motor Controllers 1,2, 3, and 4

Inputs Power In: Battery inputDesired Motor Speed: Input of desired motor speed

Outputs Motor Control: Sends a command to control the speed of themotors.

Functionality Receives desired positioning of the motors and sends commands to motorto control the speeds.


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Module Ultrasonic Sensors (LV-MaxSonar-EZ4)


Outputs Data Out: Sensor data to microcontroller.

Functionality Sends sensed data to microcontroller via a pulse width signal.

Module Barometer (MPL115A1)


Outputs Data Out: Thermal Data to microcontroller.

Functionality Provide thermal data to microcontroller.

Module Accelerometer (ADXL345)


Outputs Data Out: Translational motion data to microcontroller.

Functionality Provide translational motion data to microcontroller

Module Gyroscope (L3G4200D) Inputs Power In: 3.3V Battery input

Outputs Data Out: Rotational motion data to microcontroller.

Functionality Provide angular rate data to microcontroller.

Module GPS Sensor (RXM-GPS-SR)


Outputs Data Out: Altitude and Coordinates to microcontroller.

Functionality Provide the altitude of aircraft and coordinates to the microcontroller.

!"#$%&'(")*

(JB)The circuitry required for the autonomous blimp consists mainly of power

management and the interfacing of sensors to the microcontroller. Each sensor has itsown requirements for voltage and current supplied. The battery is fixed at one value so a

low dropout regulator is needed for the sensors. The low dropout regulator needs tochosen with a high enough current rating so that each of the sensors can get their required

current. The sensors needed include a 3-axis accelerometer, 3-axis gyroscope, barometer,

GPS, and two ultrasonic sensors.

Low Dropout Regulator:

(JB)To provide the required voltage to all of the sensors, a DC/DC convertor is

needed. To step down the voltage provided from the battery, a low dropout regulator ischosen. Figure 26 shows the circuit for the LT1963A low voltage dropout.


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33

Figure 26- LT1963A – Low dropout regulator

This low voltage dropout is chosen over a standard buck convertor because of its

low cost as it already comes in a packaged IC. The LT1963A is capable of supplying1.5A of output current and the output voltage has a tunable range from 1.21V to 20V.

The input voltage can also range from 1.21V to 20V. The reason that this model of aLDO was chosen is because of its ability to provide the 1.5A of current and also because

it has an operating quiescent current of only 1mA. Another advantage of the LT1963A isthat it is optimized for fast transient response. A10#F capacitor is needed on the output to

prevent oscillations and is also used to make the output stable. Low equivalent seriesresistance polytantalum capacitors are chosen because of their good transient response

which helps the stability of the regulator. The device maintains an output of 1.21V at theADJ pin (reference to ground) and a bias current of 3#A into the ADJ pin through R2. To

set the voltage output, the equation

!!"# ! ! !"# ! !!!"

!" ! ! !"# !!"!

is used and the values of R1 and R2 can be set [8]. For our case where all of the sensorsrequire 3.3V as an input, our resistors are set to 1.2k and 2.05k, both 1% parts. The valueof R1 is made up of a 1.1k and a 1k ohm resistor. The only requirement is that R1 be less

than 4.17k to minimize errors in the output voltage caused by the ADJ pin bias current.

Accelerometer:(JB)

To sense velocity in the x and z directions a 3-axis accelerometer is used. TheADXL345 accelerometer shown in Figure 27 below measures the acceleration of gravity

as well as dynamic acceleration resulting from motion. This sensor is being used for thedetection of motion feature so that the velocity can be sensed.

R12.05k

R2

1.2kC1

10uF

C2

10uF

LT1963A

U1A

In1

SHDN2

Out5

3

GND

ADJ4

00

00

3.3V11.1V

1.21V

(28)


41/82


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35

Figure 28-L3G4200D – 3-axis gyroscope

The L3G4200D is a low-power three-axis angular rate sensor and provides the measured

angular rate through SPI. The input command will be the angle from the user as an inputso it is desired to know the angle traveled. For the same reason as the accelerometer,

either 100nF ceramic or 10#F polyester capacitors should be placed at the supplyvoltages to for decoupling. These capacitors are to be placed as close to the device as

possible. There is also a need for a second order low-pass filter on the PLLFILT pin(phase locked loop pin), this pin synchronizes driving and sensing interfaces. The supply

voltage is to be around 3.0V and the supply current required is 6.1mA [12]. For the SPIinterfacing, the SCL, SDA, and SDO pins will all use the same line as the other SPI

sensors. The CS pin however will get its own line with the microcontroller so it can beused as a chip select.

Barometer:

(JB)One of the design requirements is to send temperature data back to the user’s

GUI. The miniature SPI digital barometer MPL115A1 as shown in Figure 29 is used for

this requirement.

U2A

L3G4200D

VDD_IO1

SCL2

SDA3

SAO4

C S

5

D R D Y / I N T 2

6

I N T 1

7

R e s

8

Res9

Res10

Res11

Res12 G

N D

1 3

P L L F I L T

1 4

R e s

1 5

V D D

1 6

C3

10nFC4100nF R3

10k

0

C7

470nF

C810uF

uC

uC

uC

uC

3.0V

NC

NC

NC

NC

NCNC


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36

Figure 29-MPL115A1 – Miniature SPI Digital Barometer

The MPL115A1 is an absolute pressure sensor with SPI interfacing. This sensor iscapable of a measuring range of 50kPa to 115kPa with a + 1kPa accuracy. It can output

monotonic pressure and temperature outputs via SPI. On the CAP pin of the IC, a 1#Fcapacitor is suggested to be connected to ground as an output decoupling capacitor for the

main internal regulator. The SHDN pin is suggested to be connected to VDD for normal

operation. Among the other SPI sensors, a chip select is going to have its own connectionwith the microcontroller but the SCLK, DIN, and DOUT pins will share the other lineswith the other SPI interfacing components. The supply voltage required for the barometer

is 3.3V and the required supply current is 5 #A [7]. This current and voltage required arewithin the limits of the LDO that was chosen.

GPS:

(JB)The altitude is desired to be sent back to the user along with the coordinates of the

blimp. To do this, a GPS is used and Figure 30 shows the RXM-GPS-SR receiver that isused in the design.

Figure 30-RXM-GPS-SR schematic

The GPS can also be used to calculate the velocity as a way of double checking or

improving the accuracy of the accelerometer. The SR series receiver can acquire andtrack up to 20 satellites simultaneously in just seconds. The reason that this GPS receiver

was selected is because it was donated and the supply current required is on 31mA andthat falls under the regulations of the LDO. The supply voltage required is between 3-

U4B

MPL115A1

VDD

CAP

GND

SHDN CS

DOUT

DIN

SCLK

C9

1uFC10

1uF

0

!C

!C

!C

!C

3.3V

U4A

RXM-GPS-SR

GND1

VBACKUP2

TX3

RX4

LED5

BS6

EN7

VCC8

G N D

9

G N D

1 0

V23.3Vdc

!C

!C

!C

NC

NC

3.3V


44/82

37

4.3V and there is need of a backup battery and have that set within the range of 1.3-3.6V.The TX and RX pins on the GPS are for the serial data input and output and are to be

connected to the microcontroller. The Boot Mode Select pin is to be left open for normaloperation while the LED pin can be left open as well. The LED pin can also be connected

to a LED so it can be shown that a valid fix has been acquired and data is being received.

Ultrasonic Sensor:(JB)

To sense objects that may appear around the blimp, ultrasonic sensors are used.The ultrasonic sensors that are used are the LV-MaxSonar-EZ4. Shown in Figure 31 are

the internal passive components, LM324s, a diode array, and a PIC16F676 which allmake up the functions of the ultrasonic sensor.

Figure 31-The LV-MaxSonar-EZ4internal connections [10].

The LV-MaxSonar-EZ4 ultrasonic sensors can detect objects at a max distance of

6.45m within a 1-inch resolution. The interface output formats include a pulse widthoutput, analog voltage, and serial digital output. The analog output is not desired when

interfacing with the microcontroller. The pulse width output is where the data will be sentas a pulse width and the range of an object can be calculated using the scale factor of

147#s per inch. Using the pulse width output means that the only pins needingconnections on the ultrasonic sensor are the GND, VCC, and the PW pins. The VCC pin

can range from 2.5V-5.5V and the PW pin is what outputs a pulse width representation ofthe range. The TX pin is responsible for sending out the digital serial data so we can

leave it open. The BW and AN pins can also be left open because the analog data output


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38

is not being used. The RX pin is internally held high so it does not need to be externallyconnected to anything. The blimp is using two of these ultrasonic sensors, one connected

in front of the blimp so anything directly ahead can be detected. The other is connectedon the bottom of the blimp and facing towards the ground so that when the blimp is near

landing, the ground distance can be known.

XBee:(JB)

To transmit data between the blimp and the ground, Xbee Pro is used. Xbee Pro iscapable of transmitting data up to 300’ and only requires 63mW of transmit power. The

required transmitting current is 250mA with a 340mA peak value; the required receivingcurrent is 55mA when at 3.3V. These ratings are within the selected LDO requirements.

UART will be the interfacing environment with Xbee Pro and it will require a data outand in line with the microcontroller along with several digital input and outputs for

communication. Figure 32 shows the pin layout of the Xbee transmitter and which pinsare inputs and outputs to the microcontroller. The digital input/output pins are excess and

will not be connected to anything.

Figure 32-Xbee Pro Pin Layout

Microcontroller:(JB)

After selecting all of the sensors needed for the blimp, a microcontroller is chosen based upon how many general purpose input and output pins needed according to the

components used. Another specification of a microcontroller is that it needs four output

comparator pins for PWMs. SPI, I2C, and UART interfacing is also needed so that thereis a choice in choosing the type of communication to use. Table 7 shows a listingcomponents and which ones need general purpose IO pins on the IC.

U7B

XBEE Pro

VCC

DIN

DO8

RESET

PWM0

PWM1

Res

DTR/Sleep-RQ/D18

GND DIO4

DIO7

ON/Sleep

VRef

Assoc iate/ DIO5

DIO6

DIO3

DIO2

DIO1

DIO0

DOUT

!C

!C

!C

!C

!C

!C

!C

!C

!C

NC

NC

NC

NC

NC

NC

NC

NC

NC

0

3.3V


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39

Table 7- List of IO Pins

51A316*62

W 1Q CH =,6-

6**4*4

M7+1A*2*+ #

XU+1-G13* #

LGG*F*+1A*2*+ #

X=) %

Y)5 &

M722*+U #


47/82

40

Like other integrated circuits that are being used, decoupling capacitors need to be

added externally on every pair of power supply pins, such as VDD, VSS, AVDD, andAVSS. The voltage supplies are all connected to a voltage in the range from 2-3.6V,

which falls within the range of the selected LDO voltage. These capacitors should be a

low-ESR device and have a resonance frequency of 200 MHz. The values and type are to be 0.1uF 10-20V ceramic capacitors. These capacitors are to be placed as close to the pins of the microcontroller as possible similar to other decoupling capacitors being used.

The MCLR pin of the microcontroller is responsible for a device reset and also device programming and debugging. To ensure that the device does not reset spontaneously, a

small network of two resistors and a capacitor can be used. This MCLR pin Vin high andlow are met due to the 10k Ohm resistor shown in Figure 33 as R6, the resistor R7 has a

value of 400 Ohms and will limit any current flowing into the MCLR from the externalcapacitor. This provides protection against Electrostatic Discharge (ESD) or Electrical

Overstress (EOS). The Vcap/VDDcore pin of the microcontroller is a voltage regulatorand it needs to have a low ESR 10uF capacitor tied from it to ground to maintain the

stability of the regulator.

Battery Monitoring:

(JB)To monitor the battery charge level, a voltage divider will be used to get the

battery voltage within the range of the microcontroller pins so it can be monitored. This isdesired so that when the battery level is reaching a critical value, the user can be alarmed.

The battery voltage is 11.1V when fully charged and this voltage needs to correspond to5V, which is the max voltage that a pin on the microcontroller can see. Figure 34 shows

a simple voltage divider that can be implemented to achieve the desired range.

Figure 34- Voltage divider to monitor battery voltage

These values of R4 and R5 will be sufficient to produce a range from 0-5V that is seen bythe microcontroller. R4 is chosen to be a 100k Ohm 1% resistor and R5 is chosen to be an

80.6k, 100, and a 1.02k Ohm resistor, each 1% parts. With the values of these resistorsrelatively high, there is not much power dissipated across them. This is a desired effect

because the purpose is only to view the value of the battery voltage. The battery that ischosen has to have the voltage vs. charge characteristics understood so that the reading

can be accurate. To prevent any loading from the microcontroller on to the resistor, avoltage buffer is used using a ua741cp.

Electric Release Valve:

R4

100k

R5

81.9k

V3

11.1Vdc

0 0

!C

-

+

U91

2

3


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(MW)It may also become desirable to bring the blimp down to ground level quickly as

possible. If the blimp has a high lift force, the blimp may become uncontrollable unlesssome of the helium inside the blimp is released. It would also be considered a safety

feature to have a release system so that the blimp does not drift into any hazards

situations. Despite proper motor placement, it may be difficult to bring down a blimp ina short amount of time. One possible method of release Helium from the blimp is toutilize an electric release valve. The blimp is equipped with several rubber valves in

which a hose barb can be used to connect a $ inch hose to an electric release valve. Thesolenoid being considered is the EZ-2140-0-243-D Vera Valve. This solenoid runs on a

12 Volt input with a power output of 10.5 Watts. However, the opening of the solenoid isonly $ inches wide, but the device is suitable for air pressure up to 700 psi. When it is

become desired to bring the blimp down, the electric release valve can be triggered by avoltage signal and remain open as long as determined by the user. The possible

configuration for the release system is displayed in Figure 35. The success of operationof the Versa Valve will depend entirely on creating a sealed connection between the

blimp envelope and the electric solenoid [15]. Final results and design may not beconcluded until testing is executed with a fully inflated envelope.

Blimp

Hose Line

Air Release

Electric Release Valve

Motor 3 Motor 4

Air Valve

Figure 35- Release Valve System

Camera:(MW)

The camera being considered for surveillances purposes is a mini wireless 2.4 GHzcamera. This small camera has full color capabilities and a range of over 200 feet. The

camera has its own transmission system that will be separate from the XBee transmitter


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and/or microcontroller, and only requires a 9 volt battery to run. This allows the camerato run for about 2 hours worth of time. The camera will transmit to a base receiver,

which will connect to a RCA input device. The screen device can be a television screen,or the RCA signal can be converted to a computer monitor screen. The camera may also

be mounted and a pan and tilt servo motor system that would be attached to the gondola.

The pan and tilt system would allow the user to can full control via the RC controller.The user would be able to control the rotation of the camera while the blimp is in a stableand stationary position.

Level 1 Hardware(JB)

The hardware level 1 block diagram can be found below in Figure 36 along withfunctional requirements in Table 5.

MicroController

Camera

Proximity Sensor

PowerManagement

Battery Voltage

Motor

Controller

Wireless

Communication

Module

3-phase Motors

and Servomotor

Inertial Sensor Unit

GPS Unit

Display

ModuleRemote Control

User Input Control(Multidirectional)

Figure 36 – Hardware Level 1 Block Diagram


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Table 8 – Hardware Level 1 Functional Requirements

Module Power Management

Inputs Power In: Battery input

Outputs Power Out: To motors, motor controller, and microcontroller

Functionality Provide regulated voltage to motors, motor controller, andmicrocontroller.

Module Microcontroller

Inputs Power In: Battery inputProximity Sensor: Distance (m) of objects for failsafe

Remote Control: User directional inputRead Camera Data: Gathers live video and sends to transmitter

Read Yaw, Pitch and Roll: Positioning data (X, Y and Z AxisData)

Read Sensors: Battery (V), GPS positioning (Latitude, Longitude)and aircraft speed (m/s)

Outputs Sensor Data Out: Provide positioning sensor data to motorcontroller

Wireless Sensor Data Out: Sends video and measurement data towireless transmitter

Functionality Use battery input to supply microcontroller while reading user directionalinput data along with inertial data and directing data to motor controller

for autonomous control and compensation. Read proximity data forfailsafe and read measurement sensors and sends the signals to a wireless

transmitter.

Module Motor Controller

Inputs Power In: Battery inputPositioning Data: Microcontroller positioning sensor data in

Outputs Motors: Controls the speed, direction, and stability

Functionality Use battery input to supply motor-controller and read positioning sensordata logic from the microcontroller. Sends a signal to control the motors

speed, direction, and stability.


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Module 3- Phase Motors and Servomotor

Inputs Power in: Battery inputController Data: Signal from Motor Controller

Outputs Motors: Controls the speed and direction of flight

Functionality Use battery input to supply motors and according to the input signal from

the motor-controller, adjust the speed of the motors.

Module Remote Control

Inputs Power In: ?V BatteryUser Input Control: User directional input

Outputs Positioning Data: To wireless transceiver

Functionality Use a ?V battery to supply power to a transmitter and send user

directional input to a wireless transceiver

Module Wireless Communication ModuleInputs Power in: Battery Input

User Positioning Data: From remote controlMeasurement Sensor Data: Receive data from microcontroller

Outputs User Positioning Data: Transmit positioning data tomicrocontroller

Measurement Sensor Data: Send to user display

Functionality Use battery input to supply wireless transceiver and receives positioning

data from remote control and sends the positioning data to themicrocontroller. Receives measurement data from the microcontroller

and sends that data to the user display.

Module Display

Inputs Sensor Data In: Wireless Measurement and Video Data In

Outputs Display Video: Live video signal displayed to user

Display Measured Data: Battery (V), GPS positioning (Latitude,Longitude) and aircraft speed (m/s) displayed on a screen

Functionality Read measurement and sensor data to display to user on a screen such as battery life, GPS positioning and aircraft speed while also displaying live

video


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Software Functional Decomposition

(SP)For the blimp system, the software’s primary function is to calculate how to

control the motors in order to follow the user’s direction or self-stabilize when there is nouser-input. This requires reading sensors for determining the current attitude and

movement of the craft along with the commands from a user input device (remotecontrol) in order to arrive at new motor speeds. In addition, sensor data needs to be

formatted and relayed back to the user. Figure 37 shows this at the lowest functionalsoftware design level, encapsulating the main functionality of software for the blimp in a

single block.

Blimp Software System

Sensors

User InputFormatted

Display Data

Motor SpeedControl

Figure 37 - Software Level 0 Block Diagram

Table 9 - Software Level 0 Functional Requirements

Moving to level 1 of the design, the overall software system architecture can be

seen at a high level in Figure 38. In the diagram, there is a distinction between softwareon-board the blimp and software on the ground with the user. The diagram also shows

how data flows in the system (pictured left to right with arrows) for each platform andwhat data is needed to be communicated between the two platforms. Both the sensors

and user input are used to control the motors via the motor control algorithm. The motorcontrol algorithm needs to know the current orientation of the craft and how it is moving

Module Blimp Software System

Inputs -Sensors: on-board sensors reading blimp attitude/movement data for

motor control and weather data for display.-User Input: user-control signals telling the blimp how to move.

Outputs -Motor Speed Control: calculated motor speeds to control flight of the

blimp.-Formatted Display Data: data to be relayed to the user.

Functionality Read user inputs and sensors to determine how to control the blimp.


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to calculate how to adjust the motors to meet the desired movement and orientation of thecraft. This will be heavily based on the control system described previously.

Proximity Sensor Data

Battery Level Data

Motor Control Algorithm Attitude Data

GPS Data

User Input

Transformation

User Input Control

Motor 1 Control

Sensors

Interface

Display Coordinates

Display Altitude

Display Speed

Display Battery Level

Display

Software

Motor 2 Control

Motor 3 Control

Wireless Data Transmission

Motor 4 Control

Barometer Data

Ground / PC

Blimp / Microcontroller

Temperature Data

User Command Packet Sensor Data Packet

Blimp

Orientation/Movement

Display Air Pressure

Display Temperature


Table 10 - Software Level 1 Functional Requirements

Module Sensors Interface (Blimp)

Inputs -Proximity Sensor Data: Proximity sensor reading.-Attitude Data: Orientation data from inertial measurement unit

(gyroscope and accelerometer).-Air Pressure Data: Barometer sensor reading.

-Temperature Data: Temperature sensor reading.-GPS/Position: GPS data from on-board GPS unit.

-Battery Level Data: Voltage level reading from battery.Outputs -Sensor Data Packet: combined sensor readings to be transmitted

wirelessly.-Blimp Orientation/Movement: Data concerning the attitude of the blimp,

the current speed of the blimp (in all directions), and obstacles in proximity of the blimp.

Functionality Reads sensors, calculates the meaning of the inertial measure unit sensorsfor motor control, and directs data in the appropriate format.


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The software design is broken down further in its level 2 block diagram shown below in Figure 39. The addition of calculating velocities for x and z directions and

calculating the pitch angle are needed as inputs to the motor control system.

Additionally, modules for sending and receiving data have been added along with amodule for converting motor speeds to PWM signals to work with the electronic speedcontrol (ESC) that are actually driving each motor.

Module Motor Control Algorithm (Blimp)

Inputs -Blimp Orientation/Movement: Velocity of blimp in x and z directions,angular velocity for yaw, the current pitch angle, and distance to objectsrelative to motion.

-User Command Packet: User commanded controls.

Outputs -Motor 1 through 4 Control: Calculated motor speeds for each motor.

Functionality Implements the control system for the craft based on current orientationand movement.

Module User Input Transformation (Ground)

Inputs -User Input Control: Data from user control device.Outputs -User Commands: Data sent to the craft to direct speed and direction

based on the user’s input.

Functionality Reads user input and sends the commands to the craft wirelessly.

Module Display Software (Ground)

Inputs -Sensor Data Packet: Data to be displayed to the user.

Outputs -Display Coordinates: Coordinates displayed to user on screen.-Display Altitude: Altitude data displayed to user on screen.

-Display Air Pressure: Air pressure data displayed to user on screen.-Display Temperature: Temperature data displayed to user on screen.

-Display Speed: Speed data displayed to user on screen.-Display Battery Level: Battery level data displayed to user on screen.

Functionality Reads, formats, and displays data back to the user.


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Proximity Sensor Data

Battery Level Data

Motor Control

Algorithm Attitude Data

GPS Data

User Input

Transformation

User Input Control

Motor 1 through 4PWM Control

Read

Sensors

Display Coordinates

Display Altitude

Display Speed

Display Battery Level

Graphical

User

Interface

Wireless Data Transmission

Barometer Data

Ground / PC

Blimp / Microcontroller

Temperature Data

User Command Packet Sensor Data Packet

Display Air Pressure

Display Temperature

Motor PWM

Sequencing

Motor 1 through 4RPM

Format Data

Read Sensor

Data

Calculate

Velocities

Calculate

Pitch Angle

Read User

Commands

Package/Send Sensor

Data

Package/Send User

Commands


Order of events on blimp (main loop):1. Read Sensors2. Calculate Pitch Angle (from combination of accelerometer and gyroscope

readings)

3. Calculate Velocities4. Check for and read user commands5. Execute motor control algorithm6. Adjust generated PWM signals based on new motor speeds7. Package/send sensor data if enough time has elapsed since last send

Module Motor PWM Sequencing (Blimp)

Inputs -Motor 1 through 4 RPM: Desired RPM of motors 1 through 4

Outputs -Motor 1 through 4 PWM Control: Motor control PWM signal

Functionality Converts RPM to pulse width modulation to work with ESC.

Figure 40 - Software Level 2 Functional Requirements (for new or updated Modules)


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Module Package/Send User Commands (Ground)

Inputs

-User Input: Transformed user input for controlling craft.

Outputs -User Command Packet: User control packaged for wirelesstransmission.

Functionality Packages user commands for wireless transmission

Module Motor Control Algorithm (Blimp)

Inputs -Craft x velocity, z velocity, yaw angular velocity, pitch angle: Currentorientation and movement of the craft.

-Desired x velocity, z velocity, yaw angular velocity, pitch angle (from

user command): Desired orientation and movement of the craft.-Proximity Sensor Data: Flags for objects in range of proximity sensors

Outputs -Motor 1 through 4 RPM: Calculated motor speeds for each motor.


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Software Design

(SCP)

The software design for the blimp system consists of two computing platforms:on-board the blimp using a microcontroller (PIC) and at the user via PC (Windows-based

laptop). Wireless communication between the two platforms is made through two XBeePro RF