a system for controlling the rotation speed of a shredder motor is disclosed . it consists of a bridge rectifier circuit , a forward / reverse controlling switch , a motor speed switch , and ac motor coils . by changing a switch , it is possible to activate the following four modes : forward fast , reverse fast , forward slow , and reverse slow . a user can thus operate a shredder at high torque and low rotation speed or high rotation speed and low torque depending on the number of sheets to be shredded .