These are 3 pole motors - not necessarily steppers.  They are used to
create an exact spin speed, since you have to drive each coil
sequentially.  They require something that looks like a 3 phase AC
signal for correct operation.

One can use them as a sort of stepper, if desired, but it's not
designed for that type of work.

-Adam

On 1/11/06, John Hennessy <john@hennessy.net.au> wrote:
> Hi, I have a box full of Hard Disk Drive spindle motors recovered from IBM
> (Sun) 4.2Gig Hard Disk Drives. They have 4 connections. My question is:
> Are they Bipolar Stepper Motors ?
>
> It appears that 3 connections are active and the 4th does nothing. I
> didn't think there was a 3 wire stepper motor. Anyway I can use an L293
> motor drive IC and sequentially power each of the 3 connectors. I get a
> clean evenly spaced step requiring 12 steps for a complete rotation. This
> may double when I wire up to a PIC and energise 2 connectors at once.
> Reversing the sequence of applying power reverses the step.
>
> I'm a little surprised they worked in this configuration. I expected to
> need 4 wires to ensure that two coils where connected. If they are not
> Bipolar steppers what are they ?
>
> Thanks
>
> John.
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