Passive stability and control of quadrupedal bounding with a flexible torso

This paper studies the stability and control of passively generated bounding motions for a class of quadrupedal template models that incorporate compliant elements in their segmented torso and legs. First, the existence of self-stable cyclic bounding gaits in the presence of torso flexibility is examined. Based on numerical studies of the associated Poincaré return map in a dimensionless context, it is deduced that self-stable bounding gaits can indeed be generated through appropriate combinations of the stiffness of the torso and the stiffness of the legs. Next, the implications of this result to control design are discussed, and a hybrid controller is proposed that enhances the stability of the passively generated bounding gaits.