Exploiting free vibration of an elastic beam for stable running locomotion

Most of the conventional legged robots are based on rigid body parts connected by high-torque actuators and a sophisticated control scheme to achieve stable running locomotion. The energy-efficiency of such robots is roughly 10-100 times lower than that of animals. Recently, there has been an increasing interest in designing compliant robots which exploit body dynamics for adaptive locomotion. It was shown that free-vibration of elastic mechanical structures can generate energy-efficient hopping/walking behavior. However, the velocity of such robots is very low. From this perspective, this paper presents a novel design strategy for running robots which makes use of torsional vibration of elastic beam. We propose a simple physical model which can be used to obtain the resonance frequency of the robot during stance phase. Moreover, this model can represent the dynamic behavior of such a robot during running locomotion.