A switching kinematic model for an octapedal robot

We propose a new model to describe the horizontal motion of an eight-legged bio-inspired miniature robot. The model does not include compliance, and can capture the kinematics of the observed locomotion behavior that corresponds to an alternating tetrapod gait. We exploit symmetries and synergies to reduce the eight-legged robot to a mechanism that is composed by two switching four-bar linkages, each representing the collective effect of a tetrapod in contact with the ground. Notwithstanding its apparent simplicity, the resulting model reproduces on average the motion of the robot. In addition, by properly tuning a family of physically-relevant parameters - including touchdown and sweep angles - different motion primitives corresponding to circular and forward motions can be realized. This model represents a first step toward developing reduced-order kinematic representations of legged robots that can be used for motion planning and feedback control purposes.