Effective self-righting strategies for elongate multi-legged robots

TL;DR

This paper investigates self-righting strategies for elongate multi-legged robots by analyzing biological behaviors and developing a robot model that employs traveling waves in body motion, enhancing robustness in complex terrains.

Contribution

It introduces a biological and robophysical approach to identify effective self-righting strategies using traveling waves, with a focus on wave parameters influencing success.

Findings

Traveling wave superposition can explain self-righting behaviors.

Wave parameters like spatial frequency and amplitude are critical.

Behavior diagrams guide effective self-righting strategy design.

Abstract

Centipede-like robots offer an effective and robust solution to navigation over complex terrain with minimal sensing. However, when climbing over obstacles, such multi-legged robots often elevate their center-of-mass into unstable configurations, where even moderate terrain uncertainty can cause tipping over. Robust mechanisms for such elongate multi-legged robots to self-right remain unstudied. Here, we developed a comparative biological and robophysical approach to investigate self-righting strategies. We first released \textit{S. polymorpha} upside down from a 10 cm height and recorded their self-righting behaviors using top and side view high-speed cameras. Using kinematic analysis, we hypothesize that these behaviors can be prescribed by two traveling waves superimposed in the body lateral and vertical planes, respectively. We tested our hypothesis on an elongate robot with static (non-actuated) limbs, and we successfully reconstructed these self-righting behaviors. We further evaluated how wave parameters affect self-righting effectiveness. We identified two key wave parameters: the spatial frequency, which characterizes the sequence of body-rolling, and the wave amplitude, which characterizes body curvature. By empirically obtaining a behavior diagram of spatial frequency and amplitude, we identify effective and versatile self-righting strategies for general elongate multi-legged robots, which greatly enhances these robots' mobility and robustness in practical applications such as agricultural terrain inspection and search-and-rescue.