Dynamics model of a four-wheeled mobile robot for control applications – a three-case study

Abstract

The problem of dynamics modeling of a four-wheeled mobile robot is analyzed in this paper. All wheels of the robot are non-steered and the servomotors are used for driving the robot. Three cases of the robot drive system are considered. In the first case, two out of four wheels of the robot are independently driven, i.e., a pair of front or rear wheels. In the second case, the same wheels of the robot are driven but drive is also transmitted to the remaining wheels via toothed belts at each side of the robot. Finally, in the third case all four wheels are independently driven. Kinematic structure of the robot and its kinematics are described. The dynamics model of the robot dedicated for control applications is derived. It takes into account tire-ground contact conditions and wheel slips. The tire-ground contact conditions are characterized by coefficients of friction and rolling resistance. A simple form of the tire model, which considers only the most important effects of tire-ground interaction, is applied. The robot dynamics model also includes the presence of friction in kinematic pairs and the electromechanical model of servomotor drive unit. The presented robot dynamics model can be used for simulation-based investigations of control systems under development. Because the model was also formulated in a form linear with respect to parameters, it is possible to use it as a part of the robust or adaptive type control system.