Analysis and experimental research on the coupled motion of the foot and paddle of crab-like robot based on biological observation

Shallow water regions, characterized by complex and varied terrain as well as dense aquatic vegetation, pose challenges for traditional propeller-based propulsion systems, which can damage seabed substrates and become entangled with aquatic plants. Amphibious bionic robots, with their remarkable environmental adaptability, have emerged as a research focus for operations in shoal environments. Drawing inspiration from the walking behavior of Portunus trituberculatus (Portunus), this paper presents a walking method for a crab-like robot that incorporates a coupled foot-paddle motion. Using the direct linear transformation (DLT) algorithm, we have captured the motion trajectories of the swimming paddles (in both heart-shaped and figure-eight patterns) during the underwater locomotion of Portunus. A hydrodynamic simulation environment was established, and the robot model was simplified. Based on the simulation results, we analyzed the influence of coupled foot-paddle motion on the robot’s force distribution from three perspectives: pressure distribution maps of the swimming paddles, force curves, and vortex diagrams. Experimental validation confirmed the effectiveness of the coupled foot-paddle motion strategy in enhancing underwater walking speed, with the figure-eight flapping mode achieving an average speed increase of 11.5% and the heart-shaped flapping mode achieving an average speed increase of 9.8%. Furthermore, in terms of stability, the coupled foot-paddle motion with heart-shaped flapping exhibited superior performance.The experimental results verify the effectiveness of the foot-paddle coupled motion strategy proposed in this paper, which provides a research basis for bionic robot composite propulsion research.