Comparison of elastic configurations for energy efficient legged locomotion

Abstract

Energy efficient locomotion with the amazing agility of humans and other animals remains a challenge for legged robots. Many existing joint mechanisms for legged robots use a serial configuration which gives compliance, however this may be sub-optimal for energy efficiency. This paper investigates the energy efficiency of legged joints for stationary jumping for three configurations of the elastic and actuator elements: series, parallel and without an elastic element. The key result is that significant energy savings are possible with a parallel configuration over the series and nonelastic configurations for the range of typical animal and robot properties: mass, stance duty and toe jump height. While there are large regions where the series arrangement is more energy efficient, these are outside typical duty cycles and will be affected by significant impact losses. The results are obtained by optimizing a set of equations to find the minimum energy losses for stationary jumping. The scripts to generate the results are available as open source software.