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Unavoidable Friction Within Servo Motors

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Unavoidable Friction Within Servo Motors UC San Diego UC San Diego Electronic Theses and Dissertations Title Design of running-man, a bipedal robot Permalink https://escholarship.org/uc/item/11r612s9 Author Chen, Jin Publication Date 2011 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California University of California, San Diego Design of running-man, a bipedal robot A Thesis submitted in partial satisfaction of the requirements for the degree Master of Science in Engineering Sciences (Mechanical Engineering) by Jin Chen Committee in charge: Professor Tom Bewley, Chair Professor Prab Bandaru Professor Mauricio de Oliveira 2011 Copyright Jin Chen, 2011 All rights reserved. The Thesis of Jin Chen is approved and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2011 iii To my parents and my brother, whose supports of my education are ever so generous iv TABLE OF CONTENTS Signature Page ........................................................................................................iii Dedication ............................................................................................................... iv Table of Contents..................................................................................................... v List of Figures.........................................................................................................vii List of Tables............................................................................................................ix Acknowledgement....................................................................................................x Abstract of the Thesis..............................................................................................xi Chapter 1 Introduction 1.1 Goal of the Thesis..................................................................................... 1 1.2 Summary of the Thesis............................................................................3 Chapter 2 Previous Robots that Hop and Run 2.1 Hopping Mechanism...............................................................................4 2.2 Previous Hopping Robots.......................................................................5 Chapter 3 Motors and Springs 3.1 RC Servos ............................................................................................... 11 3.2 Torsion Springs...................................................................................... 14 Chapter 4 Robot Mechanical Design 4.1 Legacy Design........................................................................................ 15 4.2 Design Overview................................................................................... 15 4.3 Selection of Torsion Springs.................................................................. 19 4.4 Desired Leg Joints Kinematics.............................................................. 20 4.5 Design of Ankle with Spring and Lever............................................... 21 4.6 Design of Leaf Spring Foot.................................................................... 25 4.7 Torsion Spring Bias Mechanisms.......................................................... 26 4.8 Weight and Friction Reduction............................................................. 27 Chapter 5 Simulation, Control and Electronics 5.1 Modeling and Simulation of Robot ...................................................... 29 5.2 Electronics .............................................................................................. 30 5.3 Software Overview................................................................................ 32 5.4 Hopping Algorithm............................................................................... 34 5.5 PD Control Design................................................................................. 38 Chapter 6 Test Results, Summary and Future Work 6.1 Test on Hopping Gait............................................................................ 41 v 6.2 Implementation of Running Gait.......................................................... 44 6.3 Result of Springy Foot Test.................................................................. 45 6.4 Discussion on the Design Shortcoming................................................ 45 6.5 Conclusion.............................................................................................. 47 6.6 Future Work........................................................................................... 47 References References ........................................................................................................... 52 Appendices Appendix 1 Bill of Materials............................................................................. 53 vi LIST OF FIGURES Figure 2.1: Big dog robot by Boston Dynamics (left) and leg of HyQ robot (right). ..................5 Figure 2.2: Jumping and landing robot Mowgli. .......................................................................6 Figure 2.3: : I-hop V2 developed by Chris M. Schmidt-Wetekam. Figure here is showing the “On-demand” hopping sequence. .............................................................................................7 Figure 2.4: Unnamed robot by Meyer, Sproewitz, and Berthouze. ........................................... 8 Figure 2.5 OLIE (One Leg Is Enough) seen in action..............................................................9 Figure 3.1 Digital servo HD DS120M with metal gears (left) is the driver motor of the running man robot prototype and the smaller Hitec HS-55 (right) is used to control torsion spring bias. .............................................................................................................................................. 12 Figure 3.2 RC servo control signal ......................................................................................... 13 Figure 4.1 Running man legacy design. Left figure shows robot on a test stand. Right figure shows the details of right knee joint........................................................................................ 15 Figure 4.2 CAD model of the leg prototype with caption of the main mechanical features. .... 16 Figure 4.3: Actual picture of robot prototype fixed to a pair of vertical linear sliders .............. 17 Figure 4.4 Side view of CAD model of the Running man prototype (left) and the sketch on the right showing dimensions between joints. Segments of legs are defined as follows: 1. hip; 2. thigh; 3. shin; 4. ankle............................................................................................................ 18 Figure 4.5 Kinematics of joints. ............................................................................................. 21 Figure 4.6 Design of an ankle with spring pulling a lever that actuates the up-and-down of foot. .............................................................................................................................................. 23 Figure 4.7 Figures shows the changes of lever dimension as the foot move down. ................. 24 Figure 4.8 Figure left shows the force decreases as the foot is pushed upward. Right figure show the corresponding torque............................................................................................... 24 Figure 4.9 Picture of spring feet made of polycarbonate.. ....................................................... 25 Figure 4.10 Photo of the gear train that controls the bias of right-knee torsion spring. Gears are machined delrin.. ................................................................................................................... 26 Figure 5.1 Simulation screen... ............................................................................................... 30 Figure 5.2 National Instrument sbRIO board... ....................................................................... 31 Figure 5.3 Motor control schematics... ................................................................................... 32 Figure 5.4 Calibration of potentiometer readings. The step in the blue line shows backlash of gears...................................................................................................................................... 34 Figure 5.5 States of each hopping cycle starts compression when the robot leg is bent low to store the energy, then the leg is extended to push itself upward, eventual the robot is the air in the flight stages...................................................................................................................... 36 vii Figure 5.6 Difference in angles .............................................................................................. 37 Figure 5.7 Plot of voltage during a calibration. Amplitude of 2.5 V marks the reference angle of both hip and knee angles, at 55 and 110 degree respectively. Voltages drop as the angles lower to 35 and 80 respectively.............................................................................................. 38 Figure 5.8 Root Locus plot..................................................................................................... 40 Figure 5.9 Step response of closed loop system. ..................................................................... 40 Figure 6.1Test results showing hip angle and knee angles using hopping................................ 42 Figure 6.2 A zoom-in from
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