xJus: A Hexapedal Robot with a Passively Flexible Spine

Abstract

Hexapedal running robots have been a central platform for research in biologically-inspired locomotion over the last decade. These machines aim to capture the remarkable levels of stability and energy e ciency achieved by natural hexapods like cockroaches, while maintaining simplicity through one degree-of-freedom per leg actuation and high-level open-loop trajectory generation. However, animals such as mammals and reptiles also heavily employ the flexibility of their bodies for locomotion, an e ect not replicable with the rigid chassis of previous designs. In this paper we present preliminary experimental data from xJus - the first segmented hexapod with an adjustable-stiffness passively compliant spine, designed to store body energy and reduce waste by minimizing conflicting internal forces. Results show a reduction in required motor torques when spinal compliance is introduced on at terrains, as well as improved capability to overcome large obstacles. Discussed are our mechanical, electronic, and software design approaches in building a modular and low-cost machine, as well as experimental methods and initial findings.