Serpentine motion of a trimaran robot

Abstract

An aquatic robot is proposed that moves due to the motion of an internal flywheel. The body of the robot represents a trimaran that consists of a capsule and three floats rigidly attached to it. The floats are submerged into the water and ensure that the capsule is afloat. The horizontal cross-section of each float has the shape of an airfoil. The body moves in a horizontal plane. The rotation axis of the internal flywheel is vertical. The control system makes the flywheel to oscillate, which results in oscillations of the robot body together with the floats. It is known that, when an airfoil oscillates in pitch in fluid, a thrust force is produced. As a result, the center of mass of the body moves along a serpentine trajectory. The goal of the study is to describe the effect of geometrical parameters of the robot and coefficients of the control law on the average speed of propulsion. A quasi-steady model is used to describe the hydrodynamic forces acting upon the trimaran. In order to take into account non-steady effects, added masses are considered. This approach allows for describing the robot dynamics with the ODE system. Numerical simulation of the system behavior is performed. Attracting periodic solutions are found using the relaxation method. Parametric analysis of such solutions is performed. A laboratory model is manufactured, and a series of experiments is performed. It is shown theoretically and experimentally that the speed of propulsion of the robot depends non-monotonically on the control frequency.