Effect of arm swinging and trunk twisting on bipedal locomotion

It is expected that human locomotion, in which the trunk twists and arms swing, provides stability as well as compensation for the angular momentum because the trunk and arms are placed over legs and then their position and the acceleration influence the bipedal locomotion. This paper presents a bipedal robot equipped with a trunk, embedding a viscoelastic joint and two arms away from the midline of the trunk. Physical experiments show that a passive oscillation of the viscoelastic trunk joint around the yaw axis vertical to the ground and a swing of heavy arms provided an oscillation of zero moment point (ZMP) in the lateral direction and a small oscillation in the anteroposterior direction. This is despite the fact that the robot does not have a roll joint and the arm swings back and forth. Numerical analysis supports the results of the physical experiments through a simple model and by expressing ZMP trajectory, showing that the arm swinging facilitates antiphase locomotion in which right arm and left leg swings ahead and vice versa.