Sea star inspired crawling and bouncing

TL;DR

This paper presents a hierarchical control model inspired by sea star tube feet and nervous system, demonstrating robust locomotion and transitions between crawling and bouncing, with implications for biology and robotics.

Contribution

The study introduces a novel hierarchical control framework for sea star locomotion, combining biomechanics and neural-inspired control laws, and predicts gait transitions observed in experiments.

Findings

Robust forward crawling achieved on various terrains.

Model predicts transition from crawling to bouncing.

Hierarchical control captures key features of sea star locomotion.

Abstract

The oral surface of sea stars is lined with arrays of tube feet that enable them to achieve highly controlled locomotion on various terrains. The activity of the tube feet is orchestrated by a nervous system that is distributed throughout the body without a central brain. How such a distributed nervous system produces a coordinated locomotion is yet to be understood. We develop mathematical models of the biomechanics of the tube feet and the sea star body. In the model, the feet are coupled mechanically through their structural connection to a rigid body. We formulate hierarchical control laws that capture salient features of the sea star nervous system. Namely, at the tube foot level, the power and recovery strokes follow a state-dependent feedback controller. At the system level, a directionality command is communicated through the nervous system to all tube feet. We study the locomotion gaits afforded by this hierarchical control model. We find that these minimally-coupled tube feet coordinate to generate robust forward locomotion, reminiscent of the crawling motion of sea stars, on various terrains and for heterogeneous tube feet parameters and initial conditions. Our model also predicts a transition from crawling to bouncing consistent with recent experiments. We conclude by commenting on the implications of these findings for understanding the neuromechanics of sea stars and their potential application to autonomous robotic systems.