Sea-star inspired locomotion*

Sea stars have numerous specialized ‘tube feet’, that enable them to achieve highly-controlled locomotion on various terrains from rocky to smooth surfaces. A tube foot consists of soft, water-filled, muscular membranes that extend and contract through changing the hydraulic pressure. Inspired by the biomechanics of the tube feet, we propose a low-order model for a soft actuator consisting of active and passive force elements. The active element can produce either pulling or pushing forces, which correspond to contraction and extension of the tube foot, respectively. We then study the locomotion of a distributed mass driven by several such actuators. Specifically, we investigate the stability of walking by minimally-coupled multiple actuators. We find that even though the dynamics of a single foot is unstable when carrying a load, the interaction of multiple actuators can result in a stable forward locomotion.  This system offers a new paradigm for walking using soft actuators, which exhibits great performance in terms of walking stability.