Stride Period Adaptation for a Biomimetic Running Hexapod

Jorge G. Cham
Jonathan K. Karpick
Mark R. Cutkosky

Center for Design Research
Stanford University
Stanford, CA 94305-2232, USA
contact: jgcham@cdr.stanford.edu

Abstract

We demonstrate an adaptation strategy for adjusting the stride period in a hexapedal running robot. The robot is inspired by discoveries about the self-stabilizing properties of insects and uses a sprawled posture, a bouncing alternating-tripod gait, and passive compliance and damping in the limbs to achieve fast (over 4 body-lengths per second), stable locomotion. The robot is controlled by an open-loop motor pattern that activates the legs at fixed intervals. For maximum speed and efficiency, the  stride period of the pattern should be adjusted to match changes in terrain (e.g. slopes) or loading conditions (e.g. carrying an object). An ideal adaptation strategy will complement the design philosophy behind the robot and take advantage of the self-stabilizing role of the mechanical system. In this paper we describe an adaptation scheme based on measurements of ground contact timing obtained from binary sensors on the robot's feet. We discuss the motivation for the approach, putting it in the context of previous research on the dynamic properties of running machines and bouncing multi-legged animals, and show results of experiments.