Subsea crab bounding gait of leg-paddle hybrid driven shoal crablike robot

Abstract This paper presents the design principles of a novel subsea propulsion pattern named as crab bounding gait for the shoal crablike robot and the gait experimental results. The concept of leg-paddle hybrid driven shoal crablike robot is developed for shoal environment; the robot moves on the seabed by employing six 3DOFs walking legs and swims by two 3DOFs swimming paddles. The proposed gait is derived by mimicking the movement mode of biological swimming crab when preying or being attacked underwater. Three aspects of gait planning, including gait process planning, kinematics modelling and trajectory planning, and subsea dynamics analyzing in back stance phase and flight phase by considering hydrodynamic factors such as water resistance and buoyancy, are discussed in this work. Experimental results of subsea crab bounding gait are presented and used to make a comparison with the bionic wave gait; the current and pitch angle of body centroid are monitored in real time. It is demonstrated that the average motion speed improves by 54%, and the total power consumption of crab bounding gait is 14.5 W, which enables that the total cost of transport (TCoT) decreases from 6.8 to 3.7 against bionic wave gait.