A typical electronic speed control system is normally designed to track a speed level through reference signal or sample feed extracted from lever of a motor throttle, joystick, or other similar feedback source, and auto adjust the PWM rate on the motor through a proportionately switched FET device. The controlling is implemented by varying the PWM duty cycle at the gate or base of the switching control transistors, resulting in a proportionate amount of speed variation on the motor. One downside of these controller at lower speeds is the emission of noise from the motor due to narrower PWMs which may be quite wide apart giving rise to RF interference unless of-course it is dealt with suppressors and snubbers. These speed controller modules may have different configurations and specifications depending on which type of motors is being used. As you will find under the following articles that for brushed motors the PWM control is applied to the armature of the motor, while industrial induction type of motors working with electromagnetic field winding may have controller adjusting the the magnetic flux of the field winding to regulate its speed. For unique cases such as for brushless motors the control is achieved by implementing a calculated switching of the involved multiple sets of winding position across a fixed magnet rotor. More on such concepts can be studied by referring to the following in-depth analysis.
