In this paper the equations of motion and the control of the RoboTenis system are presented. The dynamic model is based upon Largrangian multipliers. The main innovation is the use of forearms of non-neigligible inertias (1.315 Kg) in the dynamic model of the manipulator for the development of control strategies. A PD control law (nonlinear feedforward PD control) is applied. Several trajectories have been programmed and tested on the prototype. The experimental results demonstrated that the speed and acceleration of the robot can be satisfying the proposed task.