3-wire stepper motor? need help on understanding.

Hi all,

So I was able to find a salvaged stepper motor from a laser printer, and think I have figured out the 13 wires coming out of it. I disassembled it and found the following:

3 wires are for the electromagnets ( I assume a center tapped coil). there are 6 coils on the PCB within the motor case. 8 wires are for the Hall-effect sensors ( 2 for sensor power and 6 for sensor pull-off, 3 hall-effect sensors placed 120* apart) They look like tiny white squares. then there is some sort of rounded square-wave pattern formed into a circle on the back of that pcb. there are 2 wires for that.

Soo, all the stepper motors I have come into contact thus far have just been the 4-wire variety, and this is just throwing me for a loop.

Anyone have any idea how this should work? I put an ohm meter to the 3 leads, and no matter which combo I do, they are all within 2-3 ohms of eachother.

Any help on this subject would be appreciated.



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This sounds less like a stepper and more like a brushless DC motor. If this is indeed what it is, without the controller it's vitrually useless without a lot of work. I suppose there are some three-coil steppers out there, but this is a common arrangement for brushless DC motors.

-- Gordon

Reply to
Gordon McComb

Clearly it's a brushless DC servomotor. Not sure about that "rounded square wave" thing. Picture?

Is this the mirror drive motor or the paper drive motor?

You can probably run the thing using only the three drive lines (the ones that go to the electromagnets) with a controller like this:

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But you won't be able to servo down to zero speed with tight position control without a more elaborate controller.

John Nagle


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John Nagle

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