Investigation of a Bipedal Platform for Rapid Acceleration and Braking Manoeuvres

Abstract

Rapid acceleration manoeuvres have been avoided by researchers due to the aperiodicity and complexities of this motion. With the recent improvements in optimal control, this paper presents the first examination of a biped completing a time optimal sprint, starting and ending in rest, to provide insight for parameter choices of a robotic platform. In particular, a realistic linkage morphology is used with the limitation of a pre-specified actuator to choose the nominal leg length and gear ratio. Due to the size of the optimisation problem, a brute force approach is used rather than including these parameters as free variables. The results provided unique motion trajectories for time optimal behaviour with the models reaching near steady state motion and performing manoeuvres that are seen in a biped's biological counterpart. We then show that access to a higher mass-specific force does not improve the rapid acceleration manoeuvres, rather the friction coefficient and keeping the feet near the ground act as the limiting factor given sufficiently powerful actuators. A parabolic relationship emerged for sprint time versus linkage lengths providing valuable insight into the parameters to use for the platform design. To the authors knowledge, no prior research has focused on rapid acceleration and braking manoeuvres of a biped in one optimisation problem, let alone providing insight for the physical bipedal robotic platform.