Design of a Mobile Robotic Platform with Variable Footprint by Alexander N. Wilhelm A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Applied Science in Mechanical Engineering Waterloo, Ontario, Canada, 2007 ©A. N. Wilhelm, 2007 I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. Alexander N. Wilhelm ii Abstract This thesis presents an in-depth investigation to determine the most suitable mobile base design for a powerful and dynamic robotic manipulator. It details the design process of such a mobile platform for use in an indoor human environment that is to carry a two-arm upper-body humanoid manipulator system. Through systematic dynamics analysis, it was determined that a variable footprint holonomic wheeled mobile platform is the design of choice for such an application. Determining functional requirements and evaluating design options is performed for the platform’s general configuration, geometry, locomotion system, suspension, and propulsion, with a particularly in-depth evaluation of the problem of overcoming small steps. Other aspects such as processing, sensing and the power system are dealt with sufficiently to ensure the feasibility of the overall proposed design. The control of the platform is limited to that necessary to determine the appropriate mechanical components. Simulations are performed to investigate design problems and verify performance. A basic CAD model of the system is included for better design visualization. The research carried out in this thesis was performed in cooperation with the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt)’s Robotics and Mechatronics Institute (DLR RM). The DLR RM is currently utilizing the findings of this research to finish the development of the platform with a target completion date of May 2008. iii Acknowledgements It started with the desire to combine the research depth of a Canadian Master’s degree with an exciting opportunity for robotics development in Germany. Three people at Waterloo were willing to subscribe to this unorthodox undertaking. When I could not decide, all three became my supervisors; I would like to thank Chris Clark, Jan Huissoon, and William Melek for each contributing their advice and expertise. On the other side of the Atlantic, the support of the German Aerospace Center’s Robotics and Mechatronics Institute, who made this project possible, needs to be acknowledged. Specifically, I would like thank Norbert Sporer for giving me this opportunity, as well as the other researchers and staff at the institute who made my eight month stay a very enjoyable and informative one. In particular, my thanks go to Matthias Fuchs and Werner Friedl for their guidance and assistance with starting and working on a design that they have now continued. I am grateful for being given the chance to help define this project and look forward to seeing it come to fruition in the near future. My appreciation also goes out to my friends Andreas and Bernard who helped me think through some problems that had others baffled; you certainly helped me crack the puzzle. Last but not least, I would like to thank my parents and my girlfriend Emily for their love and support irregardless of whether I was in Waterloo, Munich or Toronto. iv Table of Contents Abstract .................................................................................................................................................iii Acknowledgements ...............................................................................................................................iv Table of Contents ................................................................................................................................... v List of Figures .....................................................................................................................................viii List of Tables.......................................................................................................................................xix Chapter 1 Introduction............................................................................................................................1 1.1 Motivation ....................................................................................................................................1 1.2 Background ..................................................................................................................................1 1.3 Literature Review.........................................................................................................................5 1.4 Design Goals ..............................................................................................................................19 1.5 Thesis Contribution ....................................................................................................................32 1.6 Thesis Organization....................................................................................................................32 Chapter 2 Evaluation of Configurations...............................................................................................33 2.1 Options .......................................................................................................................................33 2.2 Evaluation Criteria......................................................................................................................34 2.3 Evaluated Configurations ...........................................................................................................38 2.4 Evaluation Results......................................................................................................................46 2.5 Chosen Configuration.................................................................................................................46 Chapter 3 Variable Footprint Mechanism ............................................................................................47 3.1 Concept.......................................................................................................................................47 3.2 Optimization of Selected Configuration.....................................................................................54 3.3 Mechanism Kinetics ...................................................................................................................56 3.4 Drive Selection ...........................................................................................................................91 3.5 VFM – Conclusions....................................................................................................................94 Chapter 4 Stability................................................................................................................................95 4.1 Stability Measure........................................................................................................................95 4.2 Analysis......................................................................................................................................99 Chapter 5 Step Passing Behaviour .....................................................................................................108 5.1 Background ..............................................................................................................................108 5.2 Simple Theory ..........................................................................................................................108 5.3 Experimental System Characterization ....................................................................................111 v 5.4 Step Passing Behaviour Experiment.........................................................................................121 5.5 Advanced Theory......................................................................................................................123 5.6 Simulation.................................................................................................................................127 5.7 Applications to Platform Design...............................................................................................132 5.8 Conclusions...............................................................................................................................138 Chapter 6 Suspension..........................................................................................................................139 6.1 Problem Definition and Goals...................................................................................................139 6.2 Background...............................................................................................................................139 6.3 Review of Options ....................................................................................................................140 6.4 Tire Only...................................................................................................................................142 6.5 Passive Spring & Damper.........................................................................................................148 6.6 Suspension: Conclusion............................................................................................................157