Type of Document Thesis Author Auchter, Joseph Author's Email Address email@example.com URN etd-04132008-124258 Title Passive Variable Camber for Wheeled Mobile Robots Degree Master of Science Department Mechanical Engineering, Department of Advisory Committee
Advisor Name Title Carl A. Moore Committee Chair Anjaneyulu Krothapalli Committee Member Jonathan Clark Committee Member Patrick Hollis Committee Member Rodney Roberts Committee Member Keywords
- Wheeled Mobile Robots
- Dextrous Manipulation
- Wheel Slip
- Variable Camber
Date of Defense 2008-03-28 Availability unrestricted AbstractWheeled vehicles typically suffer from kinematic wheel slip when moving over an uneven terrain. This wheel slip can lead to decreased localization ability, higher sensory and computational burdens, uncontrolled motion, and decreased power efficiency. In this work we explore a concept to improve the performance of wheeled mobile robots on outdoor terrain, called “Passive Variable Camber” (PVC). PVC adds an extra degree of freedom to each wheel, allowing it to tilt in a lateral direction. This motion is similar to the camber variations seen in automobiles and off-road vehicles.
In this work we study the benefits of PVC for off-road mobile robots. First, we describe a novel kinematic simulation of a 3-wheeled mobile robot equipped with PVC and moving on uneven terrain. The purpose of our simulation is to verify that a WMR equipped with PVC can traverse rough ground without kinematic slip. In order to precisely model the way that three dimensional wheels roll over uneven ground, we adapt concepts developed for modeling dextrous robot manipulators. Our method provides a concise and manageable description of the kinematics and is easily adaptable to other vehicle designs of arbitrary complexity. The resulting equations tell us the instantaneous mobility (number of degrees of freedom) of the robot/ground system. We also show a way of specifying joint velocity inputs which are compatible with system constraints.
Simulation results are presented for various types of terrain and scenarios which might be faced by autonomous vehicles operating in difficult environments. Our simulations show that the PVC-equipped robot can successfully negotiate extreme terrains without kinematic slip and with variations in camber angle in the range of -15 degrees to +15 degrees. A simulation which measured wheel slip for a standard robot without PVC indicates that the slip velocity for one wheel can be as high as 15 cm/sec for a wheel of radius 30 cm, and the resulting odometry error can be as high as 12.5% of the total distance traveled. Based on our simulation results, PVC has the potential to greatly improve the motion performance of wheeled mobile robots or any wheeled vehicle which moves outdoors on rough terrain by reducing wheel slip.
We also present the design of an experimental setup to test PVC performance in the physical world. We designed a four-bar linkage which allows for the wheel camber to vary in response to the lateral forces at the wheel/ground contact. Instrumentation is described and a procedure is presented to determine the amount of wheel slip. This setup will allow us to verify that PVC reduces slip and improves motion performance.
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