Passive dynamic walking with torso

Biped walking with torso has been achieved by approaches based on actuation or special mechanism to keep the torso upright, however, these methods more or less lose some natural dynamics of biped walker. In this paper, a solution of building a totally passive walker with torso is proposed and confirmed. A fully passive torso is articulated to the biped passive dynamic walking model with two torsion springs placed between torso and legs. The elastic elements are used to help the torso maintain upright and keep the passive dynamic characteristics at the same time. Stable gait has been found and a special dynamic phenomenon of two stable limit cycles is observed by numerical simulation. The extent to which the slope and torsion springs affect the performance of walking is shown by speed, step length and local stability.