Efficient rolling motion for snake-like robots utilizing center of gravity shift

Snake-like robots have attracted attention as robots that can travel over rough terrain where wheeled mobility mechanisms cannot. Previous research on snake-like robots has mainly focused on the biological movement of snakes; therefore, the issue of power consumption caused by driving a large number of actuators still remains unaddressed. In this study, we propose an efficient movement method using the movement of the center of gravity (COG) as a solution to the above-mentioned problem. In the proposed method, the snake-like robot is first transformed into a wheel shape, and then, some motors of the joint are moved to shift the COG and rotate the robot. Therefore, good movement efficiency can be achieved on leveled terrain by the rolling movement, and a snake-like undulating drive with high running performance can be selected on underwater and rough terrain. To realize the proposed movement method, we propose a method for switching between the rotational movement and undulation drive modes. However, the rolling motion with a COG shift needs a design of an appropriate orbit of the eccentric COG and timing of the motion stage transition. In this study, we demonstrate the rolling motion design with a simplified equation of motion. Next, experiments are conducted to verify the traveling efficiency in the proposed rolling mode, and it is proven that the method can achieve twice the traveling efficiency of the undulating motion.