DC motor speed control in the aspects of benefits is relatively simple, only the size of the control voltage can control the speed, but this kind of motor should not be operated under high temperature, flammable environment, but also because of the need to brush as current converter motor parts (motors), so they need regular cleaning brush friction caused by dirt. Motor without carbon brushes is called brushless motor. Compared with brushless motor, brushless motor is more quiet than saving electricity because of less friction between carbon brush and shaft. The production is difficult and the price is high. The AC motor can operate at high temperature, flammable environment, and do not have regular cleaning brush dirt, but it is difficult to control speed, because the speed control of AC motor to control the frequency of alternating current (or the use of induction motor, with increased internal resistance, lower motor speed at the same frequency of alternating current) control. The voltage will only affect the motor torque. General civil motors have two kinds of voltage, such as 110V and 220V. In industrial applications, there are 380V or 440V types.