Dynamics and Control of a Two-Module Mobile Robot on a Rough Surface

A two-module (two-body) locomotion system moving along a straight line on a rough horizontal plane is considered. The motion of the system is excited by a periodic change in the distance between the bodies. Friction between the bodies and the plane obeys Coulomb’s law. The conditions for the system to be able to start moving from a state of rest and the steady-state motion are studied. The friction force acting on the system is assumed to be small as compared with the excitation force, and the method of averaging is applied to the equation of motion of the system’s center of mass. On the basis of the averaged equation, necessary and sufficient conditions subject to which the system can start moving from a state of rest in a dry friction environment are obtained. The excitation law that implies a piecewise quadratic time history of the distance between the bodies is considered. For this excitation law, the system can start moving from a state of rest if the bodies have different masses and the times of increase and decrease of the distance between them do not coincide. Closed-form expressions for the steady-state velocity of the system’s center of mass are obtained and investigated as a function of the parameters of the system and the excitation law. The maximum magnitudes of the steady-state velocities and the respective values of the parameters are found. An experimental prototype of the robot under consideration was built. The experimental results demonstrate qualitative agreement with the theoretical predictions.