Hip Joint Control of a Legged Robot for Walking Uniformly and the Self-lock Mechanism for Compensating Torque Caused by Weight

This paper describes hip joint control of the legged robot, PEOPLER (Perpendicularly Oriented Planetary Leg Robot) to make the robot walk uniformly. Equations are shown expressing robot speed while 4 legs change attitude patterns periodically as the hip joint rotates. With differentiation of each equation we can find angular velocity of the hip joint so that the robot can walk forward at a constant speed. Also, we show vertical displacements of the robot in connection with the angular velocity. Moreover, we devised a leg driving mechanism composed of worms and worm wheels for compensating torque caused by weight operating on the hip joint. Typical features for worm gearing such as generating lateral and axial forces are analyzed. In order to prevent the shaft from shifting toward the axial direction, we show how strong axial stoppers should be placed on a propeller shaft connecting the worms. These considerations are verified by experiments using PEOPLER Mk.2 and a miniature sized walker.