Autonomous Ornithopter Flight with Sensor-Based Seeking Behavior by Stanley Seunghoon Baek A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering - Electrical Engineering and Computer Sciences in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Ronald S. Fearing, Chair Professor J. Karl Hedrick Assistant Professor Pieter Abbeel Spring 2011 Autonomous Ornithopter Flight with Sensor-Based Seeking Behavior Copyright 2011 by Stanley Seunghoon Baek 1 Abstract Autonomous Ornithopter Flight with Sensor-Based Seeking Behavior by Stanley Seunghoon Baek Doctor of Philosophy in Engineering - Electrical Engineering and Computer Sciences University of California, Berkeley Professor Ronald S. Fearing, Chair This thesis presents the design of autonomous flight control algorithms for a flapping- wing aerial robot with onboard sensing and computational resources. We use a 13 gram ornithopter with biologically-inspired clap-and-fling mechanism. For autonomous flight con- trol, we have developed 1.0 gram control electronics integrated with a microcontroller, inertial and visual sensors, communication electronics, and motor drivers. We have also developed a simplified aerodynamic model of ornithopter flight to reduce the order of the control system. With the aerodynamic model and the orientation estimation from on-board inertial sensors, we present flight control of an ornithopter capable of flying toward a target using onboard sensing and computational resources only. To this end, we have developed a dead-reckoning algorithm to recover from the temporary loss of the target which can occur with a visual sensor with a narrow field of view. With closed-loop height regulation of the ornithopter, we propose a method for identifying the discrepancy between the tethered flight force measure- ment and the free flight aerodynamic force. Lastly, we present a nondimensionalized analysis of a motor-driven flapping-wing system and experimentally demonstrate a resonant drive to reduce average battery power consumption for DC motor-driven flapping-wing robots. i To my wife, Jiwon ii Contents List of Figures iv List of Tables vi I Introduction and Background 1 1 Introduction 2 1.1ControlChallengesforFlapping-WingRobots................. 3 1.2AerodynamicForcesforFreeFlight....................... 4 1.3EfficientEnergeticsUsingResonantExcitation................. 4 1.4Contributions................................... 5 2 Previous Work 7 2.1FlightControlforFlapping-WingRobots.................... 8 2.2ResonantDriveforFlapping-WingRobots................... 9 II Flight Control 11 3 Ornithopter Platform and Aerodynamic Model 12 3.1OrnithopterPlatform............................... 12 3.2Designof1.0gramControlElectronics..................... 14 3.3PIDControllerforOrientationandHeightRegulation............. 16 4 Flight Forces and Altitude Regulation 18 4.1AerodynamicModel............................... 18 4.1.1 AerodynamicForces........................... 18 4.1.2 Passive Stability ............................. 20 4.2ForceMeasurements............................... 20 4.3TrackingandControlMethods.......................... 21 4.4ExperimentalResultsandDiscussion...................... 25 iii 5 Flight Control for Target Seeking 30 5.1AttitudeEstimation............................... 30 5.2PredictionofTargetLocation.......................... 32 5.2.1 TargetTrackingAlgorithm........................ 32 5.2.2 DeadReckoningtoTargetLocation................... 34 5.2.3 ControlMethod.............................. 35 5.3ExperimentalResultsandDiscussion...................... 35 III Power Efficient Design 40 6 Efficient Resonant Drive of Flapping-Wing Robots 41 6.1Analysis...................................... 42 6.2CaseStudies.................................... 44 6.2.1 CaseI:ConstantSpeed.......................... 44 6.2.2 Case II: Constant Input Voltage ..................... 46 6.3Experiments.................................... 48 IV Conclusions 56 7 Conclusions 57 7.1FlightControlofFlapping-WingRobots.................... 57 7.2ResonantExcitationofDCMotor-DrivenFlapping-WingRobots....... 58 7.3FutureWork.................................... 58 V Appendix 60 A Dynamometer for DC Motors 61 A.1EstimationofMotorProperties......................... 62 A.1.1DampingCoefficient........................... 63 A.1.2BackEMFCoefficient.......................... 63 A.1.3TorqueCoefficient............................ 65 A.2EstimationofMaximumPower......................... 65 A.3SpecificationsofSmallDCMotors........................ 66 BSchematicsofImageProc2 68 C Matlab Simulation Code for Resonant Drive 74 Bibliography 82 iv List of Figures 2.1Previousworkinsmall-scaleflapping-wingrobots................ 7 3.1Themodifiedornithopter............................. 13 3.2The1.0gramcontrolboard........................... 14 3.3BlockdiagramforthePIDcontrollers...................... 16 4.1 The coordinate systems and the forces acting on the body of ornithopter. 19 4.2Forcemeasurementsetupfortheornithopterwithaloadcell......... 21 4.3Forcemeasurementswith80%dutycycle.................... 22 4.4Measurementsofaverageforcesandwingspeeds................ 23 4.5Acameracapturedimageofafreeflyingornithopter............. 24 4.6Signalflowforclosed-loopaltituderegulation................. 25 4.7Closed-loopstepresponseofheightregulation................. 26 4.8Asequenceofvideoframesshowssuccessfulaltitudecontrol......... 27 4.9Diagramofactualforcesandmeasuredforces................. 28 4.10Closed-loopstepresponseofheightregulationwithanaddedmass...... 29 5.1 The coordinate systems and the forces generated by the wings and the propeller. 31 5.2 Prediction of target location at time k + 1 based on the current orientation and its rate at time k. .............................. 32 5.3Signalflowforclosed-looponboardcontroller.................. 34 5.4Illustrationofdeadreckoningoftargetlocation................ 35 5.5Mosaicsoftheornithopterflyingtowardthetarget.............. 36 5.6Anexperimentalresultofflightcontroloftargetseeking........... 37 5.7Asetoftrajectoriesofornithopterflightstowardthetarget.......... 39 6.1 A 5.8 gram hummingbird-inspired flapping mechanism developed at UC Berkeley 41 6.2 A load connected to a spring and a damper is driven by a DC motor through acrankarm..................................... 42 6.3 Variation of nondimensional torque in one cycle for various constant angular speed with λ = 0.1, ζm =0.1,andζ =0.1.................... 45 6.4Nondimensionaltorqueandaveragepowerforconstantmotorspeed..... 46 v 6.5 Effect of input voltages with ζm = 0.002, ζ = 0.01, and λ = 0.2535. ..... 47 6.6 Effect of damping ratio with ζm = 0.02, u = 0.25, and λ = 0.2535. ...... 49 6.7averagepowerandpowerreductionusingaspring............... 50 6.8 Measurement of motor speed and induced current with constant input voltages 51 6.9 Measurement of average power and power reduction for a flapping wing robot driven....................................... 53 6.10AnInteractiveToy’sVAMPRCornithopterwithanaddedspring....... 54 6.11 Measurement of average power and power reduction for an Interactive Toy’s VAMPRCornithopter............................... 55 A.1BenchtopdynamometerforDCmotors..................... 62 A.2AcircuitmodelforaDCmotor......................... 62 A.3Anexampleofmotorspeed,motorvoltage,andtheirratio........... 64 A.4 Motor torque vs. motor speed for various input voltages. .......... 65 B.1 Schematics of ImageProc2 - microcontroller, gyroscope, flash memory, and cellphonecameraconnector........................... 71 B.2 Schematics of ImageProc2 - motor driver, oscillator, and infrared camera con- nector....................................... 72 B.3 Schematics of ImageProc2 - wireless transceiver, accelerometer, battery mon- itor,andvoltageregulators ........................... 73 vi List of Tables 2.1Developmentsofautonomousflight....................... 9 3.1SpecificationsoftheModifiedOrnithopter................... 13 6.1Specificationsoftheflappingmechanism.................... 50 A.1SpecificationsofDidelandVampmotors..................... 67 B.1BillofmaterialforImageProc2......................... 68 B.1BillofmaterialforImageProc2......................... 69 B.1BillofmaterialforImageProc2......................... 70 vii Acknowledgments First and foremost I would like to express my deepest appreciation to my advisor, Pro- fessor Ron Fearing, for his constant support and advice since my undergraduate study at Berkeley. Without his guidance, I would have never made this work possible. He has been really supportive of my work not only with his remarkable knowledge and keen insight in the field of robotics, but also with his kind consideration and encouragement. I feel very privileged and thankful to have him as an advisor. Moreover, as a senior in life, he has always been available to give me invaluable advice whenever I needed one. I would like to thank Professor J. Karl Hedrick, for his invariant consideration and advice, for serving on my qualifying examination committee as well as my dissertation committee. His nonlinear dynamic systems class has also expanded my understanding of control systems. I am very grateful to Professor Pieter Abbeel for serving on my dissertation committee, and especially for his feedback for the thesis. His insightful comments and suggestions have made the thesis much stronger. I would also like to express my appreciation for the efforts of Professor Robert Dudley and Seth Sanders, who served on my qualifying examination committee.