A roller-skating/walking mode-based amphibious robot

•We describe a roller-skating/walking mode-based quadruped amphibious robot.•The new wheeled robot has two on-land actuating modes: walking and roller-skating.•A braking mechanism installed on each leg is proposed to apply brake for the robot.•The mechanism is also used as a transformation mechanism for mode switching.•We present a closed-loop control method to control the direction of movement.

An amphibious spherical robot capable of motion on land as well as underwater is developed to implement the complicated underwater operations in our previous research. In order to improve the speed performance of the spherical robot on a slope or comparatively smooth terrains, we propose a new roller-skating mode for the robot by equipping a passive wheel on each leg to implement the roller-skating motion in this paper. A braking mechanism is designed to transform the state of each passive wheel between free rolling and braking states by compressing and releasing the spring, which is controlled by the vertical servo motor on each leg. Besides, in order to improve the walking stability of the wheeled robot in longitudinal direction, a closed-loop control method is presented to control the stability of the direction of movement while walking. Therefore, we conduct the experiments on smooth terrains and down a slope to evaluate the performance of the roller-skating motion, including gait stability and velocity. Finally, plenty of walking experiments are conducted to evaluate the ability of directional control.