Performance of a Powered Simple Rimless-Wheel across Level Ground

Legged transport is the most versatile form of locomotion available to humans and animals. Walking is a complex motion and the best legged robots of today are not able to walk as adeptly as a human. Many different models for walking have been studied by other researchers, ranging from a single rigid body in two dimensions, to systems with many links and actuators moving in three dimensions. Previous simulation work predicted that legged robots can have the same energy efficiency as a rolling wheel, but this has yet to be demonstrated in an experimental prototype. This experimental research examines the dynamics of a simple model for walking called a rimless wheel. Passive dynamic rimless wheels are shown to naturally walk down a flat inclined surface but have not been studied extensively. With an addition of a small power source, the rimless wheel would demonstrate walking on level ground. The dynamics of the powered rimless wheel would be extended to the existing passive dynamic collision-less rimless wheel which might be capable of very efficient legged locomotion. An experimental approach helps us understand the system dynamics allowing us to measure all of the mechanisms of energy loss in the system. Thus, it will allow for a clear comparison between the performance of the simple and future collision-less model. Our model consists of two rigid bodies (i.e. Assembled Wheel Frame and Torque Rod), connected via a single pin joint. The torque rod is controlled by DC motors. Initially, the gait was powered by a heuristic control algorithm. Currently, the gait is powered by a closed-loop disturbance rejection controller to maintain the absolute angular position of the torque rod which applies a torque to the rimless wheel. We would next study to power the gait with an open-loop controller for the speed of the motor. Along with a control system, a mobile data acquisition system consisting of angular rate gyro sensors, has been built and tested which records absolute angular velocity of the two rigid bodies. The device appears capable of level ground walking. Stable periodic gaits are expected to exist and are achievable with the prototype. Locomotion across level ground is possible for this powered simple rimless wheel prototype. Once stable periodic gaits are achieved, further work will explore the changes in motion and power consumption as control and physical parameters are varied.