THE DEVELOPMENT OF AUTOPILOT SYSTEM FOR AN UNMANNED

AERIAL VEHICLE (UAV) HELICOPTER MODEL

SYARIFUL SYAFIQ BIN SHAMSUDIN

UNIVERSITI TEKNOLOGI MALAYSIA

iii

Dedication

This thesis is dedicated to:

My family for their patience and support during my study,

My friends for brightening my life with their friendship and showing me that life has

no greater reward to offer than a true friend.

iv

ACKNOWLEDGEMENTS

I believe that I am truly privileged to participate in this fascinating and

challenging project as a research member since 2004. I would like to give my deepest

gratitude to my supervisor Professor Ir. Dr. Hj. Abas Ab. Wahab, who has guided

and encouraged my work with such passion and sincerity for knowledge, teaching

and care. I would like also to thank Associate Professor Dr. Rosbi Mamat for his

guidance, insight and vision on this project.

I am pleased to acknowledge the financial support of Ministry of Higher

Education Malaysia (MOHE) via Research Management Centre (RMC), Universiti

Teknologi Malaysia under fundamental research grant vot 75124 and Tabung

Pembangunan Industri-UTM for scholarship awarded.

I would like to thank my research fellows Mohamad Hafiz Ismail, Nik

Ahmad Ridhwan and Mohd Syukri Ali for their help, advice and cooperation for

many years. I would like to thank Mohamed Yusof Radzak, Mohd Daniel Zakaria,

Mohd Anuar Adip and Nor Mohd Al Ariff Zakaria for encouraging and supporting

my research efforts in PIC programming, Control Theories, RC helicopter system

and hardware intergration.

I would like to thank all the technicians in Aeronautic and Robotic

Laboratories of Universiti Teknologi Malaysia for all the help given during the

development of test rig and autopilot system for UTM autonomous helicopter

project.

My speacial thanks go to my family. I would like to thank my parents, who

taught me to take chances for better things in my life. Also my gratitude to my

grandmother, who has offered me unconditional love and care. I thank my sisters for

v

their care and encouragement during my study and I would like to wish them all the

best in their studies and careers.

In retrospect, this project did start humble but has grown to be a success as

now. There are many happy times and many dispointing moments, but now I am

very happy because all the hardship I had to go through mostly alone finally paid off.

vi

ABSTRACT

The aim of this research project is to develop an autopilot system that enables

the helicopter model to carry out autonomous hover maneuver using on-board

intelligence computer. The main goal of this project is to provide a comprehensive

design methodology, implementation and testing of an autopilot system developed

for a rotorcraft-based unmanned aerial vehicles (UAV). The autopilot system was

designed to demonstrate autonomous maneuvers such as take-off and hovering flight

capabilities. For the controller design, the nonlinear dynamic model of the Remote

Control (RC) helicopter was built by employing Lumped Parameter approach

comprising of four different subsystems such as actuator dynamics, rotary wing

dynamics, force and moment generation process and rigid body dynamics. The

nonlinear helicopter mathematical model was then linearized using small

perturbation theory for stability analysis and linear feedback control system design.

The linear state feedback for the stabilization of the helicopter was derived using

Pole Placement method. The overall system consists of the helicopter with an on-

board computer and a second computer serving as a ground station. While flight

control is done on-board, mission planning and human user interaction take place on

ground. Sensors used for autonomous operation include acceleration, magnetic field,

and rotation sensors (Attitude and Heading Reference System) and ultrasonic

transducers. The hardware, software and system architecture used to autonomously

pilot the helicopter were described in detailed in this thesis. Series of test flights were

conducted to verify autopilot system performance. The proposed hovering controller

has shown capable of stabilizing the helicopter attitude angles. The work done for

this project gives solid bases and chances for fast evolution of Universiti Teknologi

Malaysia autonomous helicopter research.

vii

ABSTRAK

Hasrat utama projek penyelidikan ini adalah untuk membangunkan satu

sistem pemanduan automatik bagi membolehkan model helikopter menjalankan misi

berautonomi dengan hanya menggunakan keupayaan pengkomputeran pintar. Tesis

ini disediakan adalah untuk menerangkan dengan terperinci kaedah rekabentuk,

pelaksanaan dan pengujian sistem pemanduan automatik yang dibangunkan pada

pesawat rotor tanpa juruterbang. Sistem pemanduan automatik direka bagi

melakukan misi berautonomi seperti penerbangan berlepas dan apungan. Bagi

rekabentuk pengawal, model dinamik tidak linear bagi helikopter kawalan jauh telah

dibina menggunakan kaedah Pengumpulan Parameter melibatkan empat subsistem

yang berbeza yang terdiri daripada dinamik badan tegar, aktuator, sayap berputar dan

proses penghasilan daya dan momen. Model matematik helikopter tidak linear yang

diperolehi akan dilinearkan menggunakan teori perubahan kecil untuk kegunaan

analisis kestabilan dan rekabentuk suapbalik linear. Suapbalik keadaan linear untuk

penstabilan helikopter dapat diperolehi menggunakan kaedah Penetapan Kutub.

Sistem keseluruhan terdiri daripada sebuah komputer pada helikopter dan komputer

kedua sebagai pengkalan bumi. Pengawalan helikopter dijalankan oleh komputer

helikopter manakala operasi perancangan misi dan interaksi pengguna dilakukan di

pengkalan bumi. Penderia yang digunakan untuk operasi berautonomi termasuklah

penderia pecutan, medan magnet dan putaran serta penderia ultrasonik. Sistem

perkakasan dan perisian yang digunakan untuk pemanduan berautonomi helikopter

telah dibincangkan dengan lebih lanjut dalam tesis ini. Beberapa siri ujikaji

penerbangan telah dijalankan bertujuan untuk mengesahkan prestasi sistem

pemanduan automatik. Pengawal apungan yang direka didapati mampu untuk

menstabilkan sudut gayalaku penerbangan helikopter. Kerja-kerja yang dijalankan

untuk projek ini diharap dapat dijadikan asas dan peluang yang baik untuk

memangkin penyelidikan helikopter berautonomi Universiti Teknologi Malaysia.

viii

TABLE OF CONTENTS

CHAPTER TITLE PAGE TITLE i DECLARATION ii DEDICATION iii ACKNOWLEDGEMENT iv ABSTRACT vi ABSTRAK vii TABLE OF CONTENTS viii LIST OF TABLES xi LIST OF FIGURES xiii LIST OF SYMBOLS xix LIST OF APPENDICES xxiii

1 INTRODUCTION 1 1.1 Background of the Research 1 1.2 Research Problem Description 3 1.3 Research Objective 4 1.4 Research Scope 4 1.5 Research Design and Implementation 5 1.6 Project Contribution 7 1.7 Thesis Organization 7

2 LITERATURE REVIEW 9 2.1 Introduction 9 2.2 Principle of Rotary Wing Aircraft 11 2.2.1 The Different of Model Scaled and Full

Scaled Helicopter 18

2.3 Helicopter Dynamics Modeling and System Identification

21

2.4 Helicopter Control 24 2.4.1 Model Based Control 24 2.4.2 Model-Free Helicopter Control 27 2.5 Related Work 29 2.6 Summary 31

ix

3 HELICOPTER DYNAMIC MODELING 33 3.1 Introduction 33 3.2 Helicopter Parameters 36 3.2.1 Physical Measurement 36 3.2.2 Moment Inertia 38 3.2.3 Rotor Flapping Moment 40 3.2.4 Aerodynamic Input 40 3.2.5 Control Rigging Curve 42 3.3 Helicopter Model 45 3.4 Linearized Model 49 3.5 Main Rotor Forces and Moments 51 3.5.1 Quasi Steady State equations for Main

Rotor Dynamics 69

3.5.2 Control Rotor Model 72 3.6 Tail Rotor 78 3.7 Fuselage 79 3.8 Stabilizer Fins 81 3.9 Eigenvalues and Dynamic Mode 86 3.10 Conclusion 93

4 CONTROL SYSTEM ANALYSIS 95 4.1 Introduction 95 4.2 Regulation Layer 96 4.3 State Space Controller Design 98 4.3.1 Attitude Controller Design 99 4.3.2 Velocity Control 103 4.3.3 Heave and Yaw Control 104

4.3.4 Position Control 107

4.4 Conclusion 109

5 SYSTEM INTEGRATION 110 5.1 Introduction 110 5.2 Air Vehicle Descriptions 110 5.3 System Overview 118 5.4 Computers 119

5.4.1 PIC Microcontroller Programming Overview

121

5.5 Sensors 128 5.6 Communications 132 5.7 On-Board Computer Circuit 135 5.8 System Integration 138 5.8.1 Power Systems 139

x

5.8.2 Mounting 139 5.8.3 Component Placement 141 5.8.4 Electromagnetic and Radio Frequency

Interference (RFI) 144

5.8.5 Interfacing into the Radio Control System

144

5.9 Conclusion 147

6 SYSTEM EVALUATION 148 6.1 Introduction 148 6.2 Helicopter Support Structure 150 6.3 Preliminary Testing 151 6.3.1 AHRS Reading Test 152 6.3.2 Servo Routine Testing 155 6.3.3 Manual to Automatic Switch Testing 155 6.4 Flight Test 156 6.4.1 Manual Flight 156 6.4.2 Initial Flight Test 164 6.4.3 Partial Computer Controlled Flight 165 6.5 Conclusion 168

7 CONCLUSION 169 7.1 Concluding Remarks 169 7.2 Recommendation of Future Work 171 REFERANCES 172 APPENDIX A 182 APPENDIX B 185 APPENDIX C 189 APPENDIX D 205 APPENDIX E 211

xi

LIST OF TABLES

TABLE NO. TITLE

PAGE

2.1 Level of rotor mathematical modeling

23

3.1 Parameters of Raptor .90 helicopter for simulation model

37

3.2 Listing of variables used to determine the moments of inertia for the Raptor .90

39

3.3 Average value of moment of inertia used in simulation models

39

3.4 Analytically obtained F matrix in hover with no control rotor

86

3.5 Analytically obtained G matrix in hover with no control rotor

86

3.6 Eigenvalues and modes for six DOF model in hovering flight condition

87

3.7 Analytically obtained F matrix in hover with control rotor

89

3.8 Analytically obtained G matrix in hover with no control rotor

89

3.9 Eigenvalues and modes for eight DOF model in hovering flight condition.

90

4.1 Maximum values for height response parameters-hover and low speed according to ADS-33C

105

5.1 Helicopter PWM receiver output channels

115

5.2 The PIC18F2420/2520/4420/4520 family device overview

120

5.3 Rotomotion AHRS3050AA specifications 130

xii

5.4 EasyRadio ER400TRS transceiver pinout diagram

133

5.5 Weight and balance log

143

6.1 SANWA RD8000 transmitter setup 160

xiii

LIST OF FIGURES

FIGURE NO. TITLE

PAGE

1.1 The research project implementation flow chart

6

2.1 The total lift-thrust force acts perpendicular to the rotor disc or tip-path plane

13

2.2 Forces acting on helicopter in hover and vertical flight

13

2.3 Forces acting on the helicopter during forward, sideward and rearward flight

14

2.4 Tail rotor thrust compensates for the effect of the main rotor

15

2.5 Effect of blade flapping on lift distribution at advancing and retreating blade

17

2.6 Cyclic pitch variation in cyclic stick full forward position

17

2.7 Typical model scaled helicopter rotor head with hingeless Bell-Hiller stabilizer systems

19

2.8 The stabilizing effect of the Bell-Hiller stabilizer bar

21

2.9 SISO representations of helicopter dynamics

25

3.1 Raptor Aircraft’s 0.90 cu in (15 cc) aircraft manufactured by Thunder Tiger Corporation, Taiwan

34

3.2 X-Cell .60 rotor head designs showing the main blade attachment

35

3.3 The stabilizer bar mechanical system operation in RC helicopter

36

3.4 Raptor Precision Pitch Gauge manufactured by Thunder Tiger Corporation

42

xiv

3.5 The longitudinal cyclic rigging curve

43

3.6 The collective rigging curve

43

3.7 The lateral cyclic rigging curve

44

3.8 The directional control rigging curve

44

3.9 Typical arrangement of component forces and moments generation in helicopter simulation model

45

3.10 Free body diagram of scaled model helicopter in body coordinate system

48

3.11 Wind axes of helicopter in forward flight

49

3.12 Rotor flow states in axial motion. (a) Hover condition (b) Climb condition and (c) Descent condition

52

3.13 Induced velocity variation as a function of climb and descent velocities based on the simple momentum theory for Raptor .90

55

3.14 Inflow solutions for Raptor .90 from momentum theory

59

3.15 Rotor thrust or wing lift for Raptor .90 calculated from momentum theory

60

3.16 Azimuth angle reference point for clockwise rotor rotation viewed from above used mainly in most remote control helicopter manufactured outside US

62

3.17 Rotor swashplate and flapping angles relationship

62

3.18 Cross coupling due to the 3δ angle

64

3.19 Hub plane, tip path plane and body axes notations

67

3.20 Control rotor of the Raptor .90 helicopter

75

3.21 Force and moment generated from tail rotor sub-system

79

3.22 The horizontal and vertical stabilizer of Raptor .90

82

3.23 Poles of coupled longitudinal and lateral motion for six DOF model with no control rotor

88

3.24 Poles of coupled longitudinal and lateral motion for eight DOF model with control rotor

90

xv

3.25(a) Roll (top) and pitch (below) rate frequency responses

to lateral cyclic for Raptor .90 and X-Cell .60 in hover condition

92

3.25(b) Roll (top) and pitch (below) rate frequency responses to longitudinal cyclic for Raptor .90 and X-Cell .60 in hover condition

93

4.1 Hierarchical vehicle control system

96

4.2 A State Space representation of a plant

98

4.3 Plant with state feedback

99

4.4 Limits on pitch (roll) oscillations – hover and low speed according to Aeronautical Design Standard for military helicopter (ADS-33C)

100

4.5(a) Attitude compensator design for pitch axis response due to 0.007 rad longitudinal cyclic step command.

101

4.5(b) Attitude compensator design for roll axis response due to 0.0291 rad lateral cyclic step command

102

4.6 Compliance with small-amplitude pitch (roll) attitude changes in hover and low speed requirement specified in Section 3.3.2.1 of the Military Handling Qualities Specification ADS-33C

102

4.7(a) Velocity compensator design for longitudinal velocity mode due to longitudinal cyclic step command

103

4.7(b) Velocity compensator design for lateral velocity mode due to lateral cyclic step command

104

4.8 Procedure for obtaining equivalent time domain parameters for height response to collective controller according to Aeronautical Design Standard for military helicopter (ADS-33C)

105

4.9 Heave dynamics compensator design due to collective pitch step command

106

4.10 Yaw dynamics compensator design due to tail rotor collective pitch step command.

106

4.11 Compliance with small-amplitude heading changes in hover and low speed requirement specified in Section 3.3.5.1 of the Military Handling Qualities Specification

107

xvi

ADS-33C

4.12(a) Helicopter responses due to 6m longitudinal position step command

108

4.12(b) Helicopter responses due to 6m lateral position step command

108

5.1 Thunder Tiger Raptor .90 class helicopter equipped with two stroke nitromethane engine with 14.9 cc displacement

111

5.2 Side frame system and engine mounting in Raptor .90 main structure

112

5.3 Swashplate mechanism

113

5.4 SANWA RX-611 receiver and actuator (servo) connections

116

5.5 The gyro automatically corrects changes in the helicopter tail trim by crosswind

117

5.6 SANWA RD8000 PPM/FM/PCM1/PCM2 hand held transmitter

118

5.7 Overview of autopilot system developed

119

5.8 The pinout diagram of PIC18F4520 microcontroller

120

5.9 Screen shot of PICBasic Pro Compiler IDE

121

5.10 PicBasic Pro programming flowchart in roll attitude stabilization

123

5.11 Attitude stabilization operations in roll attitude stabilization

124

5.12 Code fragment used in the initiate stage

125

5.13 Code fragment used in the switching stage

126

5.14 Code fragment used in the execution stage

127

5.15 The low dynamic AHRS (AHRS3050AA) from Rotomotion, LLC

129

5.16 The Polaroid 6500 Ranging module from SensComp

131

5.17 The RF04 and CM02 modules used in the research project

132

xvii

5.18 Easy Radio transceiver block diagram

133

5.19 MAX232 application circuit

134

5.20 Typical system block diagram

134

5.21 The minimum circuit required by the PIC16F877A in order to operate

135

5.22 The flight computer circuit board

136

5.23 Schematic design of on-board computer drawn in EAGLE version 4.13 by CadSoft

137

5.24 Generated board from schematic circuit drawn in EAGLE version 4.13 by CadSoft

138

5.25 The avionic box integration with UAV helicopter platform

140

5.26 The avionic box design and the mounting points to helicopter frames

141

5.27 Component placements on the avionic box

142

5.28 AHRS mounting design

142

5.29 The autopilot system integration into radio control system

145

5.30 Manual to automatic switch connections

146

5.31 Automatic-manual switch locations on the SANWA RD8000 transmitter

146

6.1 Six degree of freedom (DOF) testbed

149

6.2 The helicopter testbed geometry

149

6.3 Helicopter support structure mounting point

150

6.4 The spherical plain bearing

150

6.5 Testbed two DOF joint

151

6.6 AHRS output data format

153

6.7 LED connections to PIC18F4520 Port B 154

xviii

6.8 AHRS reading testing on protoboard

154

6.9 Manual to automatic switch operation testing

155

6.10 Carburetor adjustment chart

158

6.11 Throttle servo installations

160

6.12 Blade pitch and collective travel setting

161

6.13 Blade tracking adjustment

162

6.14 Flybar/Stabilizer bar paddles setup

162

6.15 Tail rotor blade pitch setting

163

6.16 Tail centering adjustment setting

164

6.17 The Initial flight test

165

6.18 Partially computer control flight test

166

6.19 Experiment results of attitude (roll angle) regulation by autopilot system

166

6.20 Experiment results of attitude (pitch angle) regulation by autopilot system

167

6.21 Experiment results of attitude (yaw angle) regulation by autopilot system

167

xix

LIST OF SYMBOLS

aM Main rotor blade lift curve slope

ao Lift curve slope

0a Rotor blade coning angle

1sa Longitudinal flapping with respect to a plane perpendicular to

the shaft

1sb Lateral flapping

cM Main rotor chord

hM Main rotor hub height above CG

hT Tail rotor height above CG

lH Stabilizer location behind CG

lT Tail rotor hub location behind CG

m Mass flow rate

nes Gear ratio of engine shaft to main rotor

nT Gear ratio of tail rotor to main rotor

p, q, r Angular velocities about the x-, y- and z- axes

rpm Rotation per minute

u, v, w Translational velocities along the three orthogonal directions

of the fuselage fixed axes system

au , av , aw Fuselage center of pressure velocities along x, y and z axis

wu , wv , ww Airmass (gust) velocity along x, y and z axis

v Velocity at various stations in the stream tube

iv Inflow at the disc

Vav Vertical stabilizer local v-velocity

Faw Fuselage local w-velocity

xx

Haw Local horizontal stabilizer w-velocity

x State vector

cx Control actuation sub-system state vector

fx Fuselage sub-system state vector

px Engine sub-system state vector

rx Rotor sub-system state vector

1A Lateral cyclic pitch

dA Rotor disc area

eAR Effective aspect ratio

1B Longitudinal cyclic pitch

αLC Lift curve slope from airfoil data

HLC α Horizontal tail lift curve slope

VLC α Vertical fin lift curve slope

0DC Profile drag coefficient of the main rotor blade

FDC Fuselage drag coefficient

MDoC Main rotor blade zero lift drag coefficient

maxMTC Main rotor max thrust coefficient

TDoC Tail rotor blade zero lift drag coefficient

maxTTC Tail rotor max thrust coefficient

QC Torque coefficient

CG Center gravity

Ixx Rolling moment of inertia

Iyy Pitching moment of inertia

Izz Yawing moment of inertia

Iβ Main rotor blade flapping inertia

Kβ Hub torsional stiffness

l Distance from the pivot to the body CG

oI Moment contribution of the supporting structure

SMP + Oscillating period

xxi

PWM Pulse width modulation

eQ Engine torque

R, M, N Moment terms in roll, pitch and yaw directions

RM Main rotor radius

RT Tail rotor radius

HS Effective horizontal fin area

SV Effective vertical fin area FxS Frontal fuselage drag area

FyS Side fuselage drag area

FzS Vertical fuselage drag area

Sβ Stiffness number

T Rotor thrust

cV Climb velocity

dV Rotor descent velocity

W Weight of the UAV’s model

X, Y, Z Forces term in x, y, z directions FuuX , F

vvY , FwwX Fuselage effective flat plat drag in the x, y and z axis

VuuY Vertical stabilizer’s aerodynamic chamber effect

VuvY Vertical stabilizer’s parameter for lift slope effect

minHZ Horizontal stabilizer’s parameter for stall effect

HuuZ Horizontal stabilizer’s aerodynamic chamber effect

HuwZ Horizontal stabilizer’s parameters for lift slope effect

trimrδ Tail rotor pitch trim offset

0λ , 1cλ , 1sλ Rotor uniform and first harmonic inflow velocities in

hub/shaft axes

iλ Inflow ratio at rotor disc

βλ Flapping frequency ratio

colδ , lonδ , latδ , pedδ Main rotor collective pitch, longitudinal cyclic, lateral cyclic

and tail rotor collective

xxii

γ Lock number

γfb Stabilizer bar Lock number

ρ Atmosphere density

µ Advance ratio

θ , φ , Ψ Euler angles defining the orientation of the body axes relative

to the earth

0θ Local blade pitch

1θ Blade twist angle

ψ Rotor blade azimuth angle

Ω Main rotor speed

nomΩ Nominal main rotor speed

Subscript

M, T, F, H, V Representation for main rotor, tail rotor, fuselage, horizontal

stabilizer and vertical stabilizer

xxiii

LIST OF APPENDICES

Appendix TITLE

PAGE

A System and Control Matrices

182

B Pitch Mechanism Of Stabilizer And Main Rotor Blades

185

C Microcontroller Programming Code

189

D PIC18F2420/2520/4420/4520 Microcontroller Pinout Descriptions

205

E List of Publications

211

CHAPTER 1

INTRODUCTION

1.1 Background of the Research

Agile and precise maneuverability of helicopters makes them useful for many

critical tasks ranging from rescue and law enforcement task to inspection and

monitoring operations. Helicopters are indispensable air vehicles for finding and

rescuing stranded individuals or transporting accident victims. Police departments

use them to find and pursue criminals. Fire fighters use helicopters for precise

delivery of fire extinguishing chemicals to forest fires. More and more electric power

companies are using helicopters to inspect towers and transmission lines for

corrosion and other defects and to subsequently make repairs. All of these

applications demand dangerous close proximity flight patterns, risking human pilot

safety. An unmanned autonomous helicopter will eliminate such risks and will

increase the helicopter’s effectiveness. The first major step in developing unmanned

autonomous helicopter is the design of autopilot control system for the craft itself.

The work presented in this thesis is to develop an autopilot control system for a

helicopter model in autonomous hovering.

An unmanned aerial vehicle (UAV) indicates an airframe that is capable of

performing given missions autonomously through the use of onboard sensors and

manipulation systems. Any type of aircraft may serve as the base airframe for a UAV

application. Traditionally, the fixed-wing aircrafts have been favored as the

platforms simply because their simple structures, efficient and easy to build and

2

maintain. The autopilot design is easier for fixed-wing aircrafts than for rotary-wing

aircrafts because the fixed-wing aircrafts have relatively simple, symmetric, and

decoupled dynamics.

However, rotorcraft-based UAVs have been desirable for certain applications

where the unique flight capability of the rotorcraft is required. The rotorcraft can take

off and land within limited space and they can also hover, and cruise at very low

speed. The agile maneuverability of model scaled helicopter or remote control (RC)

helicopter sold in commercial market can be useful for an unmanned surveillance

helicopter in a hard to reach or inaccessible environment such as city and mountain

valley. Unmanned surveillance helicopter offers a lot benefits in search and rescue

operations, remote inspections, aerial mapping and offer an alternative option for

saving human pilot from dangerous flight conditions (Amidi, 1996).

Beside these advantages, helicopters are well known to be unstable and have a

faster and responsive dynamics due to their small size. Model scaled helicopter can

reach pitch and roll rates up to 200 deg/s with stabilizer bar, yaw rates up to 1000

deg/s and produces thrust as high as two or three times the vehicle weight (Mettler et

al., 2002a). The helicopter dynamics are inherently unstable and require velocity

feedback as well as attitude feedback to stabilize and control. Velocity feedback

needs the accurate velocity estimates, which can be obtained by the use of an inertial

navigation system. The inertial navigation system in turn requires external aids so

that the velocity and position estimates do not diverge with the uncompensated bias

and drift of the inertial instruments, i.e., accelerometers and rate gyroscopes. Another

irony is that, even though UAVs are typically smaller than the full-size manned

vehicles, they usually require more accurate sensors because the demanded sensor

accuracy is higher when the vehicle is smaller.

An autopilot system is a mechanical, electrical, or hydraulic system used to

guide a vehicle without assistance from a human being. In the early days of transport

aircraft, aircraft required the continuous attention of a pilot in order to fly in a safe

manner and results to a very high fatigue. The autopilot is designed to perform some

of the tasks of the pilot. The first successful aircraft autopilot was developed by

Sperry brothers in 1914 where the autopilot developed was capable of maintaining

3

pitch, roll and heading angles. Lawrence Sperry has demonstrated the effectiveness

of the design by flying his aircraft with his hands up (Nelson, 1998). Modern

autopilots use computer software to control the aircraft. The software reads the

aircraft's current position and controls a flight control system to guide the aircraft.

As an unmanned vehicle, issues such as remote sensing, terrain and obstacle

recognition, radio link and data acquisition must be solved for absolute reliability.

The design must be proven to work given the constraints of the environment especially

due to lack of immediate and flexible human intervention available on board. An

autonomous control mechanism should be able to accommodate and manage all of

the issues mentioned above in real-time. It also must be able to plan its flight and

mission goals without continuous human guidance. As general remarks, the

autonomous helicopter is built basically by putting together state-of-the-art

navigation sensors and high performance onboard computer system with real-time

software control on commercially available remote-control helicopter model (Shim,

2000). The autonomous unmanned helicopter system design problem alone

encompasses many challenging research topics such as system identification, control

system architecture and design, navigation sensor design and implementation, hybrid

systems, signal processing, real-time control software design, and component-level

mechanical-electronic integration. The vehicle communicates with other agents and

the ground posts through the broadband wireless communication device, which will

be capable of dynamic network internet protocol (IP) forwarding. The vehicle will be

truly autonomous when it is capable of self-start and automatic recovery with a

single click of a button on the screen of the vehicle-monitoring computer.

1.2 Research Problem Description

Among many issues that must be addressed in the important area of

autonomous helicopter, this thesis will cover three important issues only, i.e. the

helicopter mathematical modeling and identification, hardware, software and system

integration and control system design. To begin with, in order to determine the most

effective control strategy that governs the overall architecture of a model scaled

4

helicopter, a detailed knowledge of the structure and functions of the helicopter in

the form of a mathematical model is necessary. Secondly, the analytical

mathematical model must then be provided with physical parameters accurately

representing a real helicopter model. This analytical mathematical model of

helicopter is important for the design of an autopilot system that provides

artificial stability to improve flying qualities of helicopter model. Lastly, a good

waypoint navigation planning method that fundamentally guides an on-board

computer control mechanism must be devised.

1.3 Research Objective

The objective of this research study is to develop an autopilot system that

could enable the helicopter model to perform autonomous hover maneuver using

only on-board intelligence and computing power.

1.4 Research Scope

The scopes set forth for the research work as follows:

i. Establishing scaled helicopter model dynamic characteristics for the

control system design of autopilot system

ii. Developing an electronic control system that enables the helicopter

model to perform its mission goal.

iii. Fabricating and testing the electronic control system (autopilot)

performance on helicopter model in autonomous hovering.

5

1.5 Research Design and Implementation

In order to design an autopilot system for scaled model helicopter, a

performance and stability analysis will be conducted using several physical

measurements, experimental testing and similarity analysis. The helicopter model is

derived from a general full-sized helicopter with the augmentation of servo rotor

dynamics. The nonlinear model derived from general full-sized helicopter model will

be simplified through linearization in order to obtain a linear model controller design.

The helicopter platform was then integrated with navigation sensors and onboard

flight computer. Linearized control theory will be applied for helicopter stabilization

using the model obtained. After the design of low-level vehicle stabilization

controller, vehicle guidance logic will be developed. The vehicle guidance logic can

be used as a user interface part on the ground station and sequencer on the UAV side.

The complete autopilot system integration with the helicopter had been done after all

the electronics were built and installed considering several factors such as power

requirement, mounting, electromagnetic and radio interference. The implementation

of the project research is shown in Figure 1.1

6

Figure 1.1 The research project implementation flow chart

Start

Literature Review

System Identification and Modeling of Helicopter Dynamic

Hardware and Vehicle Integration

The Design of Control System • Attitude Control • Speed Control • Heave and Yaw Control

Flight Test to Determine Helicopter Performance under Autonomous Control of the Autopilot System

Finish

Report Writing

7

1.6 Project Contribution

The project contributions are as follows:

i. Simulation models for controller design, stability and performance

analysis of a UAV helicopter model had been developed.

ii. The low level stabilization controller had been designed based on the

control theory developed from the simulation model.

iii. The prototype of autopilot system integration with the helicopter was

developed taking into consideration the power requirement, mounting,

electromagnetic and radio interference.

iv. A prototype of UAV helicopter capable of hovering autonomously

had been developed. This is the major break through in the effort of

developing a completely autonomous UAV helicopter.

1.7 Thesis Organization

This thesis is organized into seven chapters. The first chapter introduced the

motivation, research objective, scopes of work and contribution of this project.

Chapter 2 reviews the UAV development history, principle of rotary wing

aircraft, helicopter dynamic modeling, control and autonomous system design are

also explained in this chapter.

Chapter 3 presents the helicopter dynamic modeling procedures and

simulation results while Chapter 4, Hardware, Software and Vehicle Integration,

described the hardware and software development of the system and system

integration into the helicopter model.

Chapter 5 presents the control design methodology and result for each

controller for the autopilot system.

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Chapter 6 presents the flight test conducted in order to test the functionality

of the autopilot system. The preliminary tests were also conducted to ensure that the

system developed works properly.

In the final chapter, Chapter 7, the research work is summarized and the

potential future works are outlined.