Design and Implementation of The JAviator Quadrotor an Aerial Software Testbed DISSERTATION zur Erlangung des akademischen Grades Doktor der technischen Wissenschaften Angefertigt am Fachbereich fur¨ Computerwissenschaften der Naturwissenschaftlichen Fakultat¨ der Paris-Lodron-Universitat¨ Salzburg Eingereicht von Dipl.-Ing. Rainer Karl Ludwig Trummer Eingereicht bei Univ.-Prof. Dr.-Ing. Christoph M. Kirsch Salzburg, 2010 Copyright c 2010 by Rainer K. L. Trummer To Irene, Ella, and Josef. Abstract Helicopters don't look very elegant either ... but they fly reasonably well. Heinrich Dorfmann, The Flight of the Phoenix, 1965 In recent years, the research community has shown an increasing interest in autonomous aerial vehicles. Compared to fixed-wing aircraft that do not have the potential to hold some constant position in space, rotorcraft can be deployed in a much broader variety of missions, like search & rescue, traffic surveillance, area mapping, and wild-life monitoring, which are just a few examples of civil applications. Autonomous operation with respect to scout, observation, and also combat missions are further examples that give reasons for the particular interest indicated by military institutions. Besides the demand for high maneuverability, rotorcraft involved in such scenarios also need to provide sufficient flight durations, payload capacities, and robustness against disturbances. The broad availability of various low-cost small-scale quadrotors that appeared over the last decade has established this type of rotorcraft as the de-facto standard platform chosen for research applications. However, the majority of research projects involving quadrotor vehicles is concerned with pure control engineering problems, paying only little or no attention to the rotorcraft design and software-specific aspects. Particularly, the platforms commonly consist of rather filigree airframes that suffer from low robustness and the propulsion systems provide insufficient payload capacities. Moreover, the control systems mostly represent classical event-triggered approaches that are typically tuned to some specific execution environment, and consequently, do not support time portability. In other words, the temporal behavior of the control-specific algorithm may vary or even be distorted largely upon changing the hardware platform. To address these drawbacks and contribute some elaborate solutions, a high-precision quadrotor aircraft, called the JAviator, is designed and built completely from scratch. The JAviator quadrotor not only stands out from other vehicles of this kind with its high mechanical integrity, it also incorporates a very efficient propulsion system that provides both either high payload capacities or relatively long flight durations. The predominant method for providing positional feedback for autonomous indoor navigation is to employ vision-based sensing systems. As a low-cost alternative, radio-frequency-based localization i is used to enable position flight control. To cope with the quite low sensing accuracy offered by this system, a sensor-fusion-based state estimation scheme is developed. It is demonstrated that the achieved autonomous-hover accuracy represents a reasonably-well performance in relation to the error in the positional information. In order to facilitate changing the execution environment, a time-portable software architecture is presented. It is shown that the temporal behavior of the control system is preserved across various hardware platforms, even in the presence of high additional workload. ii Contents Abstract i List of Figures vii List of Tables xi Acknowledgements xiii 1 Introduction1 1.1 JAviator Aircraft................................2 1.2 Quadrotor Dynamics..............................3 1.3 Related Research................................5 1.4 Main Contributions............................... 10 1.5 Thesis Outline.................................. 14 2 Quadrotor History 17 2.1 Br´eguet-Richet Gyroplane No. 1........................ 18 2.2 De-Bothezat-Jerome Helicopter........................ 19 2.3 Œhmichen's No. 2 Helicopter......................... 20 2.4 Convertawings, Model A............................ 21 2.5 Curtiss-Wright VZ-7AP............................ 23 2.6 Naito's Yuri I Helicopter............................ 24 2.7 Spectrolutions, RC Flyers........................... 26 3 Platform Development 29 3.1 Airframe Construction............................. 29 3.1.1 Design Elaboration........................... 32 3.1.2 Composites and Joints......................... 33 3.1.3 Parts and Assembly........................... 35 3.2 Propulsion System............................... 38 3.2.1 Power Transformation......................... 39 3.2.2 Thrust Generation........................... 41 3.3 Energy Distribution............................... 42 3.3.1 Power Board Development....................... 43 iii 3.3.2 Brushless-Motor Controllers...................... 47 3.4 Sensor Equipment................................ 47 3.4.1 Ultrasonic Range Finder........................ 48 3.4.2 Barometric Measurement Unit..................... 48 3.4.3 Inertial Measurement Unit....................... 50 3.4.4 Stationary Localization System.................... 51 3.4.5 Laser Distance Sensor......................... 52 3.5 Computer System................................ 53 3.5.1 JAviator Avionics............................ 53 3.5.2 Ground Station............................. 54 3.5.3 Interconnectivity............................ 54 4 Control System Design 57 4.1 Preliminaries.................................. 57 4.1.1 Aircraft Orientation.......................... 58 4.1.2 Coordinate Transformations...................... 59 4.1.3 Applied Control Principle....................... 60 4.2 Quadrotor Plant................................ 61 4.2.1 Sensor Measurements.......................... 62 4.2.2 Sampling Characteristics........................ 62 4.3 Digital Filters.................................. 63 4.3.1DT Outlier Filter............................ 63 4.3.2 FIR Low-Pass Filter.......................... 65 4.3.3 IIR Low-Pass Filter........................... 65 4.4 State Estimator................................. 66 4.4.1 Estimation Principle.......................... 66 4.4.2 EKF Formalization........................... 68 4.4.3 EKF Implementation.......................... 72 4.5 Motion Control................................. 78 4.5.1 Manual Flight Control......................... 80 4.5.2 Position Flight Control......................... 81 4.5.3 Spin Limit Extension.......................... 82 5 Software Architecture 85 5.1 Design Approach................................ 85 5.1.1 Logical Timing............................. 86 5.1.2 Communication............................. 88 5.1.3 System Layers.............................. 88 5.2 JAviator Plant................................. 90 5.2.1 RoboMaster............................... 90 5.2.2 RoboSlave................................ 90 5.2.3 MockJAviator.............................. 90 iv 5.2.4 JAP-FCS Interface........................... 91 5.3 Flight Control System............................. 91 5.3.1 JControl................................. 92 5.3.2 EControl................................. 92 5.3.3 CControl................................. 93 5.3.4 TControl................................. 94 5.4 Ground Control System............................ 94 5.4.1 Control Terminal............................ 95 5.4.2 TuningFork............................... 97 5.4.3 Location Engine............................. 98 5.4.4 GCS-FCS Interface........................... 98 6 System Performance 99 6.1 Platform Capability............................... 99 6.1.1 Lifting Capacity............................. 100 6.1.2 Flight Endurance............................ 101 6.2 Vehicle Controllability............................. 102 6.2.1 4-DOF Characteristics......................... 103 6.2.2 6-DOF Characteristics......................... 106 6.3 Time Portability................................ 110 6.3.1 Low I/O Load.............................. 111 6.3.2 High I/O Load............................. 112 7 Conclusion 115 7.1 Thesis Review.................................. 115 7.2 Future Work................................... 116 A JAviator V1 Drawings 119 B JAviator V2 Drawings 137 Team Contributions 159 Abbreviations 161 Bibliography 165 v vi List of Figures 1 Introduction1 1.1 The JAviator quadrotor \aerial software testbed"..............2 1.2 Fundamental flight maneuvers of a quadrotor helicopter...........4 1.3 Outdoor flights performed in the courtyard of the Department of Computer Sciences at the University of Salzburg..................... 11 2 Quadrotor History 17 2.1 Br´eguet-Richet Gyroplane No. 1 helicopter of 1907............. 18 2.2 De-Bothezat-Jerome helicopter of 1922.................... 19 2.3 Œhmichen's No. 2 helicopter of 1922..................... 21 2.4 Convertawings, Model A quadrotor of 1956.................. 22 2.5 Curtiss-Wright VZ-7AP \Flying Jeep" of 1958................ 23 2.6 Naito's Yuri I human-powered helicopter of 1993............... 25 2.7 Dammar's 3rd prototype of 1991 and HMX-4 flyer of 1999......... 26 2.8 Spectrolutions, X-Pro flyer of 2002 and V-Ti flyer of 2004.......... 27 3 Platform Development 29 3.1 Prototype design of the JAviator V1..................... 30 3.2 Initial design of the JAviator V2........................ 31 3.3 JAviator V2 initial design versus JAviator V2 final design......... 33 3.4 Components in the wireframe graphics of a JAviator