Synchronized swimming: collisions drive gait compatibility in undulatory robots

Many groups of organisms live in close proximity and are capable of complex collective movement. The locomotion of individual organisms, and thus bio-inspired robots, within the collective occur through periodic oscillation of internal degrees of freedom. It is a fundamental goal of swarm robotics, and more broadly active matter systems, to understand how effective collective behaviors can emerge from simple principles of interaction. In this presentation we demonstrate how groups of simple bio-inspired robots that move through lateral body undulation and interact only through contact forces can collectively locomote in close proximity. We introduce the idea of a compatible gait configuration, a metric that measures the ability for pairs of robots with fixed wavelength (λ) and phase difference (ΔΦ) to move in close proximity without colliding. Through experiment and simulation, we demonstrate that gait compatibility can be achieved through spatial re-configuration along the traveling wave direction, Δx=(λ/2π)ΔΦ. Critically, the ability to achieve compatibility is driven through contact interactions between adjacent robots within the gait cycle no long range interactions or communication is required.