Motor control from the simplest and off, starting, stopping, to clamp phase, transformer, inverter, vector, torque control, motor repair tool detail is nothing more than to make the brushless hub motor more accurate positioning, more stable speed and torque changes in more detail.
Maintenance of common motor control AC induction motors method has the following two kinds:
a. a test voltage control method: change the stator coil voltage, you can change the speed. For example, household fans, the use of switch to change the fan speed. Servo motor
b. Frequency control method: the mains frequency is 60Hz, if you use a micro controller or digital signal processor, operating rectifier component, the power switch into a different frequency, which can change the AC motor speed.
Stepper motor AC induction motor inverter, transformer control, the advantage is small, lightweight, low price, But the problem is the low efficiency of energy conversion easy to heat, electromagnetic interference noise is easy to produce strong, high noise and vibration.

To solve the above problems, academia and industry are actively involved in the DC motor, brushless DC motor to overcome. DC motor has good stability, speed should be, its input and output is almost linear between the characteristics, so that it can have a good control performance, it is widely used in high-precision control applications. However, because the brush and commutator DC motor is a mechanical friction contact with, easy to wear, sparks and electrical noise, resulting in lower reliability. Brushless motor is the DC brush  electronic circuit in lieu of, and retains the advantages of DC motor, quick starts and stops; speed proportional to the voltage; turn moment proportional to the current advantages for high-accuracy, high stability and high speed applications. The disadvantage is limited by a permanent magnet material and size, big horsepower output system, the relative increase in difficulty.