Approximated Generalized Torques by the Hydrodynamic Forces Acting on Legs of an Underwater Walking Robot

Abstract

In this paper, we present a concept of an underwater walking robot Crabster (Fig. 1) including the main missions of the robot. The main focus is on the modeling of drag and lift forces on the legs of the robot, which makes main deference of dynamic characteristics between the on-land and underwater. Drag and lift forces acting on the underwater link are described as a function of relative velocity of link with respect to the fluid using strip theory. By describing the translational velocity of link as rotational velocity of joint, we describe the drag force as a function of joint variables. Generalized drag torque is successfully derived from the drag force as a function of generalized variables and its first derivative, even though the arm has roll joint and twist angles between joints. To verify the proposed model, we conducted drag torque simulations with simple scara robot example.