Dynamic modeling and experiment of hind leg swimming of beaver-like underwater robot

Abstract. When the beaver-like underwater robot is swimming, its hind legs provide the main propulsion force for the body, which is the source of power for the robot's movement. Hind leg swimming dynamics is the basis for analyzing the generation and change of propulsion force during the robot swimming process, which directly determines how the robot swimming trajectory is planned. However, there are few researches on the swimming dynamics of the hind leg of a beaver-like underwater robot. This paper proposes a rigid–liquid fusion dynamics modeling method, which simplifies the swimming dynamics of hind legs of beaver-like robot to hydrodynamics of webbed feet and rigid body dynamics of thighs and calves. The hydrodynamics of the bendable webbed foot is established based on the integral hydrodynamics method, and the rigid body dynamic model of the thigh and calf is constructed using the Newton–Euler method. Through the force transmission, the overall swimming dynamic model of the hind leg is established, and the propulsion and lift force of the hind leg to body are obtained. The ANSYS Fluent simulation of the movement of robot's hind leg and underwater single-leg swimming experiments verify the correctness and effectiveness of the dynamics model. Comparing the theory, simulation, and experimental results of the propulsion and lift force of the robot's hind legs under bionic swimming, increased amplitude swimming, and reduced amplitude swimming, it further verifies the correctness of the proposed rigid–liquid fusion dynamic modeling method, and proves the superiority of the robot's bionic swimming trajectory. This study can provide new ideas for the leg dynamic modeling of underwater swimming robots with bendable webbed feet, and lay a theoretical foundation for exploring the swimming mechanical process of underwater robots.