Editing Motor controller (section)

== Servo controllers ==
{{Main| Servo drive| Servomechanism}}
Servo controllers are a wide category of motor control. Common features are:
* precise closed loop position control
* fast acceleration rates
* precise speed control Servo motors may be made from several motor types, the most common being:
** brushed DC motor
** brushless DC motors
** AC servo motors

Servo controllers use position feedback to close the control loop. This is commonly implemented with [[encoder (position)|position encoders]], resolvers, and [[Hall effect sensor]]s to directly measure the [[Rotor (electric)|rotor]]'s position.

Other position feedback methods measure the back [[electromotive force|EMF]] in the undriven coils to infer the rotor position, or detect the Kick-Back voltage transient (spike) that is generated whenever the power to a coil is instantaneously switched off. These are therefore often called "sensorless" control methods.

A [[servomechanism|servo]] may be controlled using [[pulse-width modulation]] (PWM). How long the pulse remains high (typically between 1 and 2 milliseconds) determines where the motor will try to position itself. Another control method is pulse and direction.