Mechanics-Based Design of Underactuated Robotic Walking Gaits: Initial Experimental Realization

This paper presents two strategies for designing underactuated, planar robotic walking gaits and for realizing them experimentally. The methods draw upon insights gained from the authors' recent work which leverages properties of the mechanics of the robot to design a controller that stabilizes walking by regulating the transfer of angular momentum about one support pivot to the next. One proposed gait design strategy is to simulate a closed-loop hybrid model of the robot under the action of the mechanics-based controller to produce an implicit periodic orbit for each set of controller parameters. The second design strategy modifies traditional usage of nonlinear optimization to produce parameterized outputs corresponding to a stable Hybrid Zero Dynamics. The novel approach is to reformulate the HZD stability constraint using the mechanics of the system and to propose an alternative to the periodic HZD orbit existence constraint through the use of an angular momentum variant of the Linear Inverted Pendulum. The two methods are used to design gaits that are implemented in experiments with the AMBER-3M robot.