Autonomous aerobatic flight of a fixed wing unmanned aerial vehicle

171 Pages·2007·2.26 MB·English

UNIVERSITEIT STELLENBOSCH UNIVERSITY
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Autonomous Aerobatic Flight of a Fixed Wing
Unmanned Aerial Vehicle
by
Willem J. Hough
Thesis presented at the University of Stellenbosch in
partial fulfilment of the requirements for the degree of
Master of Science in Engineering
(Electronic Engineering with Computer Science)
Department of Electric & Electronic Engineering
University of Stellenbosch
Private Bag X1, 7602 Matieland, South Africa
Supervisor: Prof Thomas Jones
Co-Supervisor: Mr Iain K. Peddle
March 2007
Declaration
I, theundersigned, herebydeclare that the workcontained in this thesis is my own original work
and that I have not previously in its entirety or in part submitted it at any university for a
degree.
Signature: .......................................
Date: ..........................
ii
Abstract
This thesis relates to the successful development of a flight control system to perform a range of
aerobatic manoeuvres autonomously. The project is the first to try to extend the flight control
capabilities of the Computer and Control group at the University of Stellenbosch.
A simplified mathematical aircraft model is developed which encapsulates the important dy-
namic characteristics of the airframe. It is demonstrated how computational fluid dynamics
software can be used to calculate the stability and control derivatives of a conventional air-
frame.
A vehicle independent kinematic state estimator is presented and used to obtain the complete
aircraft state vector. The estimator makes use of extended Kalman filter theory to combine a
series of low quality sensor measurements in an optimal manner. A model predictive control
strategy is then used to regulate the aircraft about arbitrary, time variant trajectories. The
controller’s architecture is not in any way specific to the aerobatic manoeuvres demonstrated in
this project.
The avionics and ground station used for the implementation of the estimator and control
algorithms are presented. The development of a hardware in the loop simulator is discussed and
used to verify the correct implementation of the respective algorithms. Finally, practical results
from two days of flight tests are presented.
iii
Uittreksel
Hierdie tesis handel oor die suksesvolle ontwikkeling van ’n vlugbeheerstelsel om ’n verskeiden-
heid akrobatiese manoeuvres automaties uit te voer. Dit is die eerste projek wat die vlugbeheer
tegnieke van die Rekenaar en Beheer groep by the Universiteit van Stellenbosch probeer uitbrei.
’nVereenvoudigdewiskundigevliegtuigmodelisontwikkelwatdiebelangrikstedinamiesekarak-
teristieke van dielugraam omsluit. Die proses demonstreer hoevloeidinamika sagteware gebruik
kan word om die stabiliteits- en beheerafgeleides van ’n konvensionele lugraam te bereken.
’n Voertuigonafhanklike kinematiese toestandsafskatter word voorgedra en gebruikom dievlieg-
tuig se hele toestandsvektor te bereken. Die afskatter maak gebruik van uitgebreide Kalman
filter teorie om ’n reeks lae kwaliteit sensormetings bymekaar te voeg in ’n optimale manier. ’n
Model voorspellendebeheerstrategie worddan gebruikom dievliegtuig te reguleer om arbitrˆere,
tyd-variante bane. Die beheerderargitektuur is nie op enige manier spesifiek tot die akrobatiese
manoeuvres gedemonstreer in hierdie projek.
Die avionika en grondstasie wat gebruik is vir die implementering van die afskatter- en beheer-
algoritmeswordvoorgedra. Dieontwikkelingvan’nhardewareindielussimulatorwordbespreek
en gebruik om die korrekte implementering van die verskeie algoritmes te bevestig. Laastens
word praktiese resultate van twee dae se vlugtoetse voorgedra.
iv
Acknowledgements
I would like to express my sincere gratitude to the following people and organisations who have
contributed to making a project of this magnitude and complexity possible:
• Prof. T.Jonesforguidingmeintotherightdirection andprovidingmewithdeeperinsight
on many topics.
• Mr. I.K. Peddle for helping me get to terms with numerous theoretical problems and his
willingness to always lend a helping hand regardless of the problem at hand.
• Denel Aerospace Systems, ARMSKOR and ATE for funding UAV related work at the
University of Stellenbosch.
• The National Research Foundation for helping fund the project during its second year.
• Jacob Venter for your valued input regarding RC problems and helping with the construc-
tion of the aircraft.
• ArnoBarnard,WillievanRooyenandJohanArendsetonameafewwhoprovidedtechnical
advice and support during various stages of the project.
• Dr. Kas Hamman for flying the aircraft.
• All my friends in the ESL, especially Johan Bijker and Carlo van Schalkwyk, for helping
me with practical tests and the many non-work related discussions.
• Laura Garbarino for her interest in my work and testing my ability to explain various
engineering related topics.
• My mother and brother for your continuous belief in me and your supportthroughout the
project.
v
Dedications
This thesis is dedicated to everyone who has contributed towards my education.
vi
Contents
Declaration ii
Abstract iii
Uittreksel iv
Acknowledgements v
Dedications vi
Contents vii
List of Figures xiii
List of Tables xvii
Nomenclature xviii
1 Introduction and Overview 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Task Description and Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Aircraft Model 4
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2.1 Axis System Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 Inertial Reference Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Body Reference Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Equations of Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Attitude Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.1 Euler Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.2 Quaternion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Forces and Moments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4.1 Gravitational . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4.2 Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.3 Aerodynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5 Non-linear State-space Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5.1 Displacement Differential Equations . . . . . . . . . . . . . . . . . . . . . 16
2.5.2 Linear and Angular Velocity Differential Equations . . . . . . . . . . . . . 17
2.5.3 Non-linear State Equations . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Kinematic State Estimator 21
3.1 Overview and Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 Optimal State Estimation Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 Kinematic Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.1 Non-linear State Equations . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3.2 Non-Linear Measurement Equations . . . . . . . . . . . . . . . . . . . . . 30
3.4 State Initialisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.5 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
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3.5.1 Calculation of Aircraft State Vector . . . . . . . . . . . . . . . . . . . . . 36
3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4 Control and Simulation 40
4.1 Overview and Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2 Controller Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2.1 Trajectory Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.2.2 Prediction Horizon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2.3 State and Control Weights . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2.4 Position Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.3.1 Conventional Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.3.2 Aileron Roll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.3.3 Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.3.4 Immelmann . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5 Avionics and Ground Station 60
5.1 Avionics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.1.1 PC104 Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.1.2 IMU CAN Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.1.3 Magnetometer/Pressure CAN Node . . . . . . . . . . . . . . . . . . . . . 66
5.1.4 Servo Controller CAN Node . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.1.5 Power Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.1.6 Cost and Mass Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.2 User Control Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
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5.3 Ground Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.3.1 Ground Station Software . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6 Hardware in the Loop Simulator 80
6.1 HILS Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.2 Simulation Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.3 HIL Distribution Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.4 Simulink Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.5 Autopilot Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7 Flight Tests 94
7.1 Flight Test Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.1.1 Wednesday the 15th of November 2006 . . . . . . . . . . . . . . . . . . . . 94
7.1.2 Friday the 17th of November 2006 . . . . . . . . . . . . . . . . . . . . . . 95
7.1.3 Friday the 24th of November 2006 . . . . . . . . . . . . . . . . . . . . . . 96
7.2 Autopilot Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.2.1 Kinematic State Estimator . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.2.2 Model Predictive Controller . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8 Summary and Recommendations 105
8.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
8.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Bibliography 108
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