Title
An Experimental Investigation of the Cobot Wheel Contact Patch

Abstract
Current research at the Laboratory for Intelligent Mechanical Systems is focused on developing a new class of passive robots called cobots, which use nonholonomic joints rather than actuated joints. The nonholonomic joint takes advantage of the nonholonomic velocity constraint imposed by a wheel to relate both linear and angular velocities. As a result, the performance of the cobot is in part dependent on how well the wheels function. This paper looks at what effect varying different wheel parameters has on the performance of the cobots. Using Taguchi methods we were able to examine how the compression of the wheel, the contact patch size, and coefficient of friction, were affected by the diameter, durometer, and profile of the urethane wheels used on many cobots. Additionally, by modifying Hertz theory for the contact of elastic bodies using an elastic foundation simplification it was possible to develop an equation for the load which was a function of measured parameters. By comparing the theoretical results with the actual results, it was then possible to determine the validity of modeling the contact using the assumptions found in Hertz theory.

Source: Master's thesis, Department of Mechanical Engineering, Northwestern University, December, 1997