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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