stepper motors

I've just been messing with an iac stepper motor. I referred to the premium channel and watched again the iac videos. I get how the voltage is reversed and how to test it now. Can anyone point me to a scanner danner video on how the motor works. IE why does it have 4 wires (or 5) for 2 or more coils, when the voltage is just reversed to alter the direction of the stepper motor.

Thanks Guys

Sorted now. A quick youtube search and all makes sense now

YouTube is awesome for learning about stuff

In case others are wondering, stepper motors are pretty much the same on the inside. There may be a number of different wires brought to the outside of the case: 4, 5, 6, or 8. Inside there are 4 coils and 8 wires and some of the wires might be connected internally to get the different number of leads coming out.

4 leads - bipolar stepper motor ONLY
5 leads - unipolar stepper motor ONLY
6 leads - unipolar or bipolar
8 leads - unipolar or bipolar

When the motor is driven with a unipolar driver one or two leads are used are common (DC ground) and the other leads are energized in the correct order to spin the motor. A unipolar drive is 'push only' it is a cheaper type of drive to build but is not able to drive the stepper motor at it full power capability.

When the motor is driven as a bipolar drive you have a push-pull type of drive. The leads to a coil swap polarity. This type of driver is more expensive to make but gets more power out of the stepper motor.

These days there are very fancy stepper drivers which can output something closer to a sine wave which gives you smoother movement and higher resolution. I'm not sure if this type of drier has made its way into the automotive world or not yet.

One curious failure mode of a stepper motor is that if you loose connection to one coil (or one side of the driver fails) it will still rotate, but roughly and typically only in one direction. It may however randomly change directions each time you try to move it. This can lead to some very odd symptoms.