An almost linear biped

We discuss the nonlinear control of a novel biped robot with three-degrees-of-freedom and two control inputs, whose dynamics are linear apart from the gravitational torque and the impact equations. We show that the equations of motion are locally feedback linearizable by nonlinear change of coordinates and nonlinear feedback in a region that includes all walking gaits of interest. We combine the feedback linearization control with control of the resulting linear system and the nonlinear impact equations to generate a stable walking gait