An effective controller and compensator is designed by using the system identification and constant structure theory to realize the effective control. The experimental results indicate the extraneous torque can be decreased by 90% and the characteristics can be improved greatly by means of this kind of method. An effective controller and compensator is designed by using the system identification and constant structure theory to realize the effective control. The experimental results indicate the the extraneous torque can be decreased by 90% and the characteristics can be improved greatly by means of this kind of method.