In this paper, a sliding mode control law is derived for a nonlinear, time varying permanent magnet synchronous motor (PMSM) driven direct drive system (DDS). A sliding controller is developed for set-point tracking. Its existence and the reaching conditions derived for the electromechanical system together with the proof of asymptotic stability by using the Lyapunov method. Experiments are performed by implementing the control law on a DSP32 based PMSM driven single link arm. The results obtained support the developed theory and demonstrate the robustness expected from the control method. The designed control methods which offer solution to common control problems could find a wide range of application especially in industries involved with the control of electrical motors, industrial robots, servomechanisms and other electromechanical systems.