Effects of swing-leg retraction and mass distribution on energy-loss coefficient in limit cycle walking

Limit cycle walkers utilizing their natural dynamics can achieve energy-efficient dynamic walking. Their heel-strike collision with the ground is generally modeled as an inelastic collision, and the discrete walking dynamics can be specified in the same manner as a rimless wheel by using the energy-loss coefficient and restored mechanical energy. Energy-loss coefficient is especially significant because it controls the gait efficiency and stability, but the value varies significantly according to the swing-leg retraction just prior to impact and robot´s mass-distribution. This paper then mathematically investigates how energy-loss coefficient changes with respect to them, and discusses the effect on the gait efficiency and stability.