The Simplest Walking Robot: A Bipedal Robot with One Actuator and two Rigid Bodies

We present the design and experimental results of the first 1-DOF, hip-actuated bipedal robot. While passive dynamic walking is simple by nature, many existing bipeds inspired by this form of walking are complex in control, mechanical design, or both. Our design using only two rigid bodies connected by a single motor aims to enable exploration of walking at smaller sizes where more complex designs cannot be constructed. The walker, “Mugatu”, is self-contained and autonomous, open-loop stable over a range of input parameters, able to stop and start from standing, and able to control its heading left and right. We analyze the mechanical design and distill down a set of design rules that enable these behaviors. Experimental evaluations measure speed, energy consumption, and steering.

I. Introduction

Small robots have the potential to conduct inspection and maintenance inside machinery spaces that other robots cannot reach, explore small crevices on other planetary bodies, or search through rubble in disaster scenarios [1], [2]. Small walking robots in particular offer unique capabilities like careful step placement or hopping to navigate obstacles, which can be particularly useful at small scales where surfaces are comparatively rough and obstacles are comparatively large.