A combined gear includes a pair of first gear and second gear having the same tooth profile and rotatably combined in a state, wherein rotation centers of the gears are coincident. The method includes selecting a kinematic constraint for the humanoid robot such as maintain the two feet in flat contact with the floor. The valves return to a closed state after the pressure or force is removed. The movement of the platform and the external heart massager is conducted simultaneously and may be coordinated manually or by a controller.