DESIGN, PROTOTYPING AND TESTING OF AN AUTONOMOUS HEXAPOD ROBOT WITH C SHAPED COMPLIANT LEGS: AbhisHex By ABHISHEK ANAND BAPAT (B.E. MECHANICAL) THESIS Presented To The Graduate Faculty Of The University Of Texas At San Antonio In Partial Fulfillment Of The Requirements For The Degree Of MASTER OF SCIENCE IN ADVANCED MANUFACTURING AND ENTERPRISE ENGINEERING COMMITTEE MEMBERS: Dr. F.Frank Chen, Ph.D, Lutcher Brown Distinguished Chair in Advanced Manufacturing Dr. Hung-da Wan, Ph.D, Associate Professor, UTSA ME Department Dr. Pranav Bhounsule, Ph.D, Assistant Professor, UTSA ME Department THE UNIVERSITY OF TEXAS AT SAN ANTONIO DEPARTMENT OF MECHANICAL ENGINEERING DECEMBER 2016 i ACKNOLEDGEMENTS This thesis project bears imprints of many individuals. I would like to take this opportunity to express my heartfelt gratitude to all of them without whom my project wouldn’t have been successful. The creation of my robot “AbhisHex” is definitely one of my biggest achievements and is a turning point of my life. I would like to extend my deep gratitude to Dr. Pranav Bhounsule whose expertise in legged robots helped me achieve AbhisHex. I am extremely thankful for his valuable suggestions, constructive criticism and constant encouragement which helped me push my limits to prove this concept. He not only supported me through smallest of the issues I wished to address but also introduced me to a completely different approach in handling and achieving things I desired. The project would not have been completed without the support of Dr. Frank Chen, Dr. Hung-Da Wan, Paul Krueger (Machine shop) and all RAM lab members Ali, Christian, Christopher, Eric, Robert and Jeoffrey who were a strong source of help, support and inspiration during all these hectic days. It was a great pleasure working with Maxon Motors USA. who virtually guided me at every minute instant while addressing all sorts of problems to get their products working. Lastly, I would like to thank the UTSA and The Department of Mechanical Engineering staff for their help extended during this project. ii ABSTRACT DESIGN, PROTOTYPING AND TESTING OF AN AUTONOMOUS HEXAPOD ROBOT WITH C SHAPED COMPLIANT LEGS: AbhisHex Abhishek Anand Bapat, M.S. Advanced Manufacturing And Enterprise Engineering The University Of Texas At San Antonio, 2016 Supervising Professor: Dr. Pranav Bhounsule, Ph.D. Animals have always inspired our intuition that legs are essential for performing gaits and actions over highly rough landscapes. In this view, legged robots can be used to maneuver over different terrains where wheeled robots cannot approach. AbhisHex was inspired from a cockroach running and walking style which helped it to overcome locomotion over any terrains. Cockroach legs are arranged in sprawled posture and are moved in a stereotypical “clock” signal pattern giving it extreme stability over all the terrains. Although the robot leg design is not similar to the cockroach but their co-ordination from stance to swing state is adjusted so as to match that of cockroach gaits. Each of the six legs is actuated by individual motors and has one degree of freedom. AbhisHex is designed in order to achieve speeds covering up to one body length per second over different terrains. The main purpose of building AbhisHex was to use it in exploration of remote locations and hostile environments like space, planets, nuclear power plants, bomb disposal, fire fighting, search and rescue where humans have life risks. iii In this thesis, a design procedure is outlined in order to systematically design an autonomous hexapod. The main features considered are mechanical structure and analysis of the body, C shaped leg design, material selection, actuating and driving mechanisms, walking gaits and speeds, payload, control architecture and cost. The hexapod was tested to stand and walk on flat grounds, slopes and uneven terrains. iv TABLE OF CONTENTS Acknowledgements…………………………………………………………………….. ii Abstract………………………………………………………………………………… iii List of Tables…………………………………………………………………………... vii List of Figures………………………………………………………………………….. viii Chapter One: History • Concept and Inspiration.............................................................................. 1 • What are legged robots ?............................................................................. 1 • Types, Comparison and Development of legged robots……….………… 2 • Wheeled robots vs Legged robots………………………………..………. 5 Chapter Two: Overview • What is RHex ?........................................................................................... 7 • Purpose of building RHex ?........................................................................... 7 • Comparison between RHex family............................................................. 7 • RHex vs AbhisHex………………………………….……………………. 11 Chapter Three: Mechanical Design and Modeling • Design of body............................................................................................ 13 • Design of C shaped leg and Gait Patterns................................................... 14 • Selection Of Material.................................................................................. 15 • 3D Drawings of Components...................................................................... 17 v • Free body diagrams (Leg + Body) ............................................................. 20 • Building of the actual body......................................................................... 21 Chapter Four: Electrical and Network Communication • List of Electrical components...................................................................... 24 • Calculations and Selection of Electrical components................................. 27 • Design of Internal Communication Diagram.............................................. 30 Chapter Five: Software Design • PI control Algorithm................................................................................... 32 • Structured Code (Maxon Studio) ............................................................... 35 Chapter Six: Simulations and Analysis • FEA Analysis on Body................................................................................ 37 • FEA Analysis on Leg.................................................................................. 39 • Simulations & Plots in SolidWorks ........................................................... 42 • Simulations in SimMechanics (MATLAB) ............................................... 45 Chapter Seven: Testing and Results • Test Setup and Prototype Testing…………………………………...…… 46 • Computing the results.................................................................................. 51 • Cost analysis................................................................................................ 54 Chapter Eight: Conclusion and Future ………………………………………….……... 56 Appendix……………………………………………………………………………….. 58 References......................................................................................................................... 72 Vita vi LIST OF TABLES Table 1: Comparison of AbhisHex and RHEX……………………………………………... 11 Table 2: Properties of Al 6061-T6……………………………………………………………. 15 Table 3: Comparison of different material properties………………………………………… 17 Table 4: Effect of gains for Kp, Ki, Kd……………………………………………………….. 34 Table 5: Cost analysis of AbhisHex……...…………………………………………………… 54 vii LIST OF FIGURES Figure 1: Arthropod Morphology………………………………………………………………….. 1 Figure 2: Toyota’s One Legged robot……………………………………………………………... 2 Figure 3: Cornel Ranger: A 4 legged Bipedal Robot……………………………………………… 3 Figure 4: A three-legged robot…………………………………………………………………….. 3 Figure 5: Boston Dynamics Big Dog: A 4 legged robot…………………………………………... 4 Figure 6: Rhex: A six legged robot………………………………………………………………... 4 Figure 7: (a) Roomba i-robot and (b) Mars Rover………………………………………………… 5 Figure 8: Research Rhex…………………………………………………………………………… 8 Figure 9: EduBot v2.0……………………………………………………………………………... 8 Figure 10: SandBot v1.0…………………………………………………………………………… 9 Figure 11: Desert Rhex: A modified Research Rhex……………………………………………… 10 Figure 12: The XRL robot…………………………………………………………………………. 10 Figure 13: X-Rhex robot…………………………………………………………………………… 11 Figure 14: Cross member frame…………………………………………………………………… 13 Figure 15: Tripod gait pattern……………………………………………………………………… 14 Figure 16: AbhisHex components list………………….…………………………………………. 20 Figure 17: (a) FBD of body and (b) FBD of leg…………………………………………………… 20 Figure 18: EPOS2 P 24/5 Controller………………………………………………………………. 24 Figure 19: EPOS2 Motherboard and 36/2 Module………………………………………………… 25 Figure 20: Maxon EC Motor………………………………………………………………………. 25 viii Figure 21: Maxon Planetary Gearhead…………………………………………………………….. 26 Figure 22: Maxon HEDL Encoder………………………………………………………………… 26 Figure 23: Batteries ……………………………………………………………………………….. 27 Figure 24: A physical layout of Internal Communication in Rhex………………………………... 31 Figure 25: MATLAB Code for PI Control Algorithm…………………………………………….. 34 Figure 26: Meshing of AbhisHex’s Body Frame…………………..……………………………… 38 Figure 27: Static Stress Analysis of AbhisHex’s Frame……………………………….…………. 39 Figure 28: Meshing of AbhisHex’s Leg………………………………….………………………. 40 Figure 29: Static Stress Analysis of AbhisHex’s Leg……………………………………………. 41 Figure 30: Strain, Displacement and Stress Analysis of AbhisHex’s Leg………………………. 41 Figure 31: Angular Displacement vs Time Plots…………………………………………………... 43 Figure 32: Reaction Force vs Time Plots………………………………………………………….. 44 Figure 33: Path traced by AbhisHex in Simulation…………………………………….…………