Passive dynamic quadrupedal walking

It has been shown that a suitably designed biped will walk passively, i.e., without actuation or control, down a shallow slope. This paper extends the concept from bipedal to quadrupedal locomotion. A simple rimless-wheel model is analyzed first to provide a few basic insights, followed by a more complex model with freely-swinging legs. The gaits found for the quadruped are similar to, but more efficient than, those of the biped. However, for any reasonable choice of physical parameters for the system, quadrupedal walking is unstable