Anisotropic body compliance facilitates robotic sidewinding in complex environments

Sidewinding, a locomotion strategy characterized by the coordination of travelling waves of lateral and vertical body undulation (referred to as the gait “template”), is observed in certain desert snakes and has been successfully reconstructed by limbless robotic systems for effective movement across diverse terrestrial terrains. Inspired by control simplification achieved via mechanical intelligence in lateral undulation [Wang et al 2023], which offloads feedback control to passive body mechanics, we developed a new kind of sidewinding limbless robophysical model. This 105 cm long device features a bilateral cable actuation system that resembles organism muscle actuation mechanisms and allows for programmable anisotropic body compliance. By varying the body compliance while sidewinding, we observed that with appropriate directional compliance the robot achieved both a lower cost of transport on hard ground and improved navigation through heterogeneities in lab (peg board) and outdoor terrains relative to experiments without compliance. When sidewinding through heterogenous environments, compliance helped minimize the effect of impeding robot-environment interactions, allowing the robot to 1) squeeze through obstacles or 2) brush by them without large changes in body orientation.