Gait-Free Planning for Hexapod Walking Robot

This paper presents a gait-free motion planning approach for quasi-static walking of hexapod walking robots on terrains with limited available footholds. The proposed approach avoids using a prescribed gait pattern allowing an arbitrary sequence of leg swings. Furthermore, it is allowed that some legs do not need to be placed on the terrain for an extended duration. The proposed method is based on a decomposition of the motion planning into: (i) finding a candidate sequence of stances and intermediate configurations representing plausible steps using a graph-search; and (ii) connecting the intermediate configurations by feasible paths satisfying the motion constraints of the walking robot. The individual one-step paths are determined using a Bézier curve-based parametrization that seems to be sufficient for the relatively simple paths of a single step, and the low-capacity parametrization yields natural-looking motion.

I. Introduction

Hexapod walking robots provide increased stability over their "competitors" such as quadruped Spot [1] and ANY-mal [2] or biped/humanoid robots such as Atlas [3]. For an exploration of highly structured, unsafe environments, such as collapsed buildings, where fast dynamic motions are undesirable, hexapod crawlers might be superior due to their inherent stability and redundancy. Hexapod walking robots can locomote using a fast, quasi-statically stable gait for which only two steps are required to complete one gait cycle, compared to four steps of a quadruped. Hexapod crawlers also do not need to use all legs for statically stable locomotion compared to quadrupeds; indeed, six is the least even number of legs that allow gait-free quasi-static movement.