1, brush refers to the commutation brush. The motor rotation is need fixed excitation (small motor is fixed magnet), the armature winding generates a magnetic field, the two field can produce force, if it is a DC motor, originally the direction of the current is not change, if not change, the armature turned half circle are the magnetic force will instead. So when the armature commutating brush can turn half circle way to switch the current direction.
Brushless motor is in the stator part, by changing the current wave alternating frequency and waveform input to the stator winding of brushless motor, it forms a magnetic field around the winding coil, which revolves around the motor's geometric axis. This magnetic field drives the permanent magnet steel rotor on the rotor to rotate.
2, there is a lot of harm to the brush.
The friction is large and the loss is large. After using the motor for a period of time, it is necessary to turn on the motor to clean the carbon brush of the motor, which is time-consuming and laborious, and the maintenance strength is no less than a family cleaning.
High fever, short life: because of the structure of motor brush, brush and commutator contact resistance is large, resulting in overall motor resistance is high, easy to heat, and the permanent magnet is a sensitive element, if the temperature is too high, will make the magnet demagnetization, motor performance, influence of brush motor life.
The efficiency is low, and the output power is small: the problem of the brush motor heating is mentioned above, largely because the current work is done on the internal resistance of the motor, so the electric energy is largely transformed into heat energy, so the output power of the brush motor is not large, and the efficiency is not high.
In addition, the inductors generated by the switching current will lead to the electric spark in the switch, which is not much used in industry.
3. The power of the brushless motor is related to the logarithm of the pole, the frequency and the frequency of the motor.