Tripedal walking robot with fixed coxa driven by periodic rocking

This paper is concerned with realization of a new kind of three-legged walking machine. The proposed robot has neither coxa joint nor knee joint, so the three legs are just rigidly fixed to each other. Instead of pursuing elaborated joint mechanism for the coxa, we equipped it with two actuators and a pair of weights, so that it can generate torque about the yaw and the pitch axes. Thus it only rocks as a reaction of the mass driving unit. We show that, by appropriate choices of oscillatory controls (i.e., amplitudes, frequencies and phases of the pitch and the yaw actuators), it is indeed possible to achieve rotation and forwarding locomotion of the tripedal robot. In particular, combination of the frequencies selects the rotation/forwarding, while combination of the phases affects the direction of forwarding. We also remark that the realized motion naturally reflects the symmetry of the body structure.