Motor controller
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A motor controller is a device responsible for regulating the voltage applied to an electric motor. An electric motor controller can be classified by the type of motor it is to drive such as permanent magnet, servo, series, separately excited, and alternating current. A motor controller is connected to a power source such as a battery pack or power supply, and control circuitry in the form of analog or digital input signals.
DC motors are typically controlled by using a transistor configuration called an "h-bridge."([Image:
]) This consists of, at a minimum, of two NPN and two PNP transistors. One NPN and one PNP transistor is activated at a time. Both NPN or PNP transistors can be activated to cause a short across the motor terminals, which can be useful for slowing down the motor from the resistance it creates.
Servos are controlled using a pulse. The pulse length determines where the motor will try to position itself. This posistion is found with a variable resistor which creates a feeback loop. As the motor turns, the resistance value changes. The resistance is then compared using a comporator until it lies within a certain margin of error. At this point the movement stops to avoid it oscilating from it continually overcorrecting.
Stepper motors are moved by rotating which coil to apply electricity to in a circular manner. They are controlled by a timing circuit. This allows extremly accurate control by changing the clock speed for the next firing. Typically these see use in such things as disk drives where precise speed control is critical.
External Links/Bibliography: Frogfot (http://www.frogfot.com/electronics.html#hbridge) DPRG (http://www.dprg.org/tutorials/1998-04a/) Template:Tech-stub