DC motor is to rely on direct current working voltage operation of the motor, widely used in tape recorders, video recorders, video machines, electric shavers, hair dryer, electronic watches, toys and other. 1 electromagnetic DC motor electromagnetic DC motor consists of stator poles, a rotor ( armature commutator ( commutator ), commonly known as ), brush, shell, bearing components, electromagnetic DC motor stator poles ( the main magnetic pole ) composed of an iron core and a field winding that forms. According to its excitation (the old standard called the exciting ) the different ways can be divided into series DC motor, DC motor, separately excited DC motor and compound wound DC motor. Because of different excitation mode, stator pole flux (by the stator magnetic pole coil excitation electricity generated ) of different. The series excitation DC motor excitation winding and the rotor winding is connected in series between the brush and the commutator, field current and armature current proportional to the stator magnetic flux, with the excitation current increases, the armature current and torque is approximately proportional to the square of the speed, torque and current increases with the rapid decline. The starting torque to rated torque 5 times above, short time overload torque can reach more than 4 times the rated torque, speed change rate is larger, no-load speed is very high ( generally do not allow the no-load operation ). Can use external resistor and the series winding series ( or parallel ), or the series winding in parallel to achieve the speed change. Shunt excited DC motor excitation winding and the rotor windings are connected in parallel, the excitation current is constant, the starting torque and the armature current is proportional to, starting current is about 2.5 times of the rated current of about. Speed with the current and torque increases slightly, short-time overload torque Rated torque 1.5 times. Speed change rate is small, from 5% to 15%. Through the weakened field constant power to the governor. Separately excited DC motor excitation winding received independent excitation power supply, the excitation current is constant, the starting torque and the armature current is proportional to. Speed variation for 5% ~ 15%. Through the weakened field constant power to increase the speed or by decreasing the rotor winding voltage to reduce speed. Compound wound DC motor stator magnetic pole in addition to the shunt winding, also fitted with the rotor winding connected in series with the series winding ( of the relatively small number of turns ). The series winding to generate a magnetic flux direction and the main winding of the magnetic flux direction, starting torque Rated torque of about 4 times the left and right sides, short time overload torque Rated torque is about 3.5 times. Speed variation rate is 25% ~ 30% ( with the series winding related). Speed through the weak magnetic field strength to adjust. Commutator bar the use of silver and copper, cadmium and copper alloy materials, high strength plastic molded into. Brush sliding contact with a commutator, provide for rotor winding armature current. Electromagnetic DC motor brush generally use a metal graphite brush or electrochemical graphite brush. Rotor iron core made of silicon steel sheet laminating, generally 12 slot, with 12 groups of armature winding, the winding is connected in series between the rear, connected with the 12 commutator bar connection.