Stepper DC Motors

Stepper DC Motors are brushless, synchronous electric motors which rely on electromagnets to rotate the internal shaft. A typical stepless electric motor will have an iron toothed cog connected around the internal rotating shaft. Around this shaft are four toothed electromagnets, positioned at equal intervals around the cog.

When switched on, one of these toothed magnets (No. 2) will attract the center cog towards it's teeth, until they are perfectly aligned. However, due to the way stepper motors are designed, the next magnet (No. 2) will be slightly offset to the teeth of the center cog. This means that when the first magnet switches off and the second magnet takes over, the cog will partially rotate so that it's teeth align with those of the second magnet. The same thing happens for the next magnet (No. 3), and finally the last (No. 4). So when all four magnets have completed a cycle of partially rotating the center cog, the cog is now displaced by a distance of ONE tooth. And so on and so forth, so quicly that the center cog rotates. 

Computer controlled steper motors are now the most widely used form of positioning motor. They have applications in CD and Floppy drives, printers, scanners, toys, automated facilities, and even satellites. They are extremely controllable due to their operation, and can often be controlled to the nearest fraction of a millimetre. However, they are not high power motors, and do require an external controller to operate.