Hard disk motor - DC or stepper?

[forgie]

Hi there. I am knocking up a prototype of something for a friend (yeah, I couldn't be more vague then that, hey!)... anyway, I somehow need to get the motor in an old hard drive to run. That's all I need to do for now. All I know about the motor is that it has 3 terminals.

Does anyone have any experience or knowledge when it comes to HDD motors? Are they normally DC or steppers? If it is a stepper, how would the coils be likely to be arranged (there's three terminals on it).

Any thoughts or wisdom would be much appreciated.

I think in the end I'll have to pull out ye olde scope and see what happens when I spin the spindle, but I don't have the time right now, so I figured if anyone has any pointers in the right direction that'd be a good start.

Thanks folks.

[Melanie]

Which motor? A Hard Disk has two. The Head Motor is a Stepper. The Spindle Motor isn't... it's a conventional DC motor.

[forgie]

It's the spindle motor we're talking about here.

So would the third terminal be some sort of encoder output to regulate a constant speed?

Any guesses as to what voltage it would run on? HDDs have 12V and 5V connections to a computer....

[Melanie]

Well, if it's a 2.5in Drive, it probably doesn't use the 12V connection.

As for the (physically) larger sizes, 12V ceratinly was for the spindle motor when I played with drives (no saying that they don't have a regulator to drop the 12v to something else nowadays - check your PCB). Going back to when I was a teenager and I used to pick up old 5.25in HDDs at the junk store for a few cents, they would have a jumper (or switches) to stagger the power-up time of the spindle motor at initial switch-on, so as not to overload the 12v line if you had multiple drives in a system.

[forgie]

It's a 3.5" drive, and I think it's about 10 years old, but I only have the skeleton (one part of the mounting chassis + spindle motor) to work on right now.

I think I'll rig up a variable regulator. Shouldn't be too hard.... I'll grab a 7805 and figure something out.

Any clues on the encoder output? Could it be a hall effect sensor or something? I have no idea what sort of sensor would be used in this type of DC servo motor. It's not THAT important that I get the feedback working, it's more so I can work out which terminal is which. I guess if I plug it into my PC scope and spin the spindle, two of the terminals should show a (relatively) constant voltage, which will hopefully be the two motor drive terminals.

Thanks for the info, Melanie.

[forgie]

Double post.....

[forgie]

I have tried applying 9V across each of the two terminals.... but it seems to act like a stepper motor!? When any particular pair of terminals has current through them, the spindle will jump to a certain position and lock there... was there any stage in HDD history when stepper motors were used in the spindles?