HDD Spindle motor help???

[Minifig666]

I have recently dismantled a computer and got a Maxtor 40GB HDD out of it. The spindle motor in the middle has 4 pins coming from the left they are labelled as this from top to bottom; MTR-C, MTR-B, MTR-A, CT. I'm guessing that's coil 3, 2, 1, and ground.
When the HDD is plugged in to a power supply it spins then stops then spins up again. This is obliviously not very useful.
How would you go about ruining this with a PICAXE? I know it will need power transistors and that sort of thing but I am a bit lost with the code. I wish to use it with an 08-M, using the input to start it and stop it and the outputs to run the transistor circuit. Can anyone give me an example of code? Thanks in advance

 

[Andrew Cowan]

I'd imagine you'd power them up with 12v (though could be 5v) in turn. You might need an H bridge to reverse the polarity of the coils.

A PICAXE probably isn't fast enough to get much speed out of it, however.

A

 

[Minifig666]

I measured 8V across the terminals so I'm geuss it is 12V accountig for PWM. I'm not quite shure what you mean by the H-Bridge though

 

[hippy]

If this is an attempt to get the HDD working and usable with a PC I wouldn't expect to get very far with a PICAXE. For the fun of getting it to spin using a PICAXE that's fair game.

I expect CT is "centre tap" but whether connected to 0V or elsewhere depends on how the motors are actually driven; is it DC stepping or some from of AC control - I have no idea. Perhaps putting a scope on the signals and seeing what they are when it is running will help. You can also do a continuity check to 0V to see if CT does connect to that or elsewhere.

From a quick Google search it seems that 3.5" HDD will likely have 12V motors and can draw over 2A when starting up. There also appears to be a number of projects driving HDD motors so it's possible and it may be worth looking at the commercial control chips designed to do that job.

 

[SAborn]

A Hdd motor is a 3 phase motor (MTR,A,B,C) are your phase wires and the 4th wire (CT)is the star connection.

You could try holding the star conection high or low and toggle the phase wires in order to get rotation, A bit like a unipolar stepper motor.

Try 3 npn transistors off the picaxe outputs connected to the phase wires and hold the star connection high. With the right order of the coils it should rotate.

Something like

low A,B ' (using the phase codes A,B,C instead of pins in example)
High C

Start:
toggle C,B
toggle B,A
toggle A,C

Goto start

You might need to rearange the order of A,B,C before it rotates.
By reversing the correct order it should reverse direction.
You might need a pause between each toggle to get enough drive, and the pause can be used as a speed control

To drive it under phase control i think the phase shift will need to be around 90 deg. out and would be rather tricky to do with a picaxe.

Have fun.

 

[Minifig666]

Yeah checking it with my multimeter it seems to be the centre tap of a star formation. It is pulled high to 5V with some sort of semiconductor as it is more resistive depending on the polarity. I hooked it up too 5V from my PSU and then probed A, B, and C in turn. The motor turned 1/3 of a rotation on each time I moved the 0V probe. Now I think I know how to go about this. Regarding my intentions for using the motor, I am planning a rotating display, probably with a SMD 28-X1 and LEDs. Thanks for all the help

 

[AndyGadget]

SABorn is right - It's a 3 phase motor - star connected.
Pulse the coils in turn but you'll need to ramp up the cycle rate otherwise it will just sit there juddering. Currents will be high.

Andy.