What kind of motor is this?

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Hi,

I have a small motor that I would like to use, but I don't know much about motors, so I don't know what it is.

It is about an inch across and has four connections. When I rotate the shaft, it turns smoothly without any clicking feel like a stepper motor might do. When I measure between the pins, I get an ohm reading of around 6.8 ohms between one pin and any one of the other three. When I measure between the other three pins, they are all 13 ohms between them.

When I attempt to look inside, I can just see the tops of some windings. It looks like there are somewhere between eight and ten windings. Or perhaps they are connected differently than it looks from the tiny slit in the top and there are four.

Anyway, if someone could tell me what kind of motor it might be so that I could then find information on it, I would appreciate it.

Thanks,

Daniel

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Standard 3-phase sensorless brushless motor like you find on the bottom of a harddrive.
Your first problem will be that it's sensorless; To detect when to switch to the next state you can use the back-EMF generated by the motor, this however can only be done when the motor is in motion so you'll have to have a startup mode to acquire position.

This article looks like useful reading. True, it's not AVR, but it looks like something one would do with an AVR:
http://www.eetasia.com/ARTICLES/...

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This would, from the resistance, seem to be a "Y" connection of the coils.

That would strongly suggest that its not an ordinary DC motor.

But, what is it? It might be an AC motor intended to be used with a phasing cap to control the direction of rotation.

It might be a stepper motor, even though you don't feel the "cogging" as it is called.

Most likely, however, it is a 3-phase "DC motor". That is, the power supply is connected to the terminal that reads the low resistance to the other three. Then, each winding is grounded, in sequence, to cause it to rotate (stepper-like).

IF it is the latter, you could use three FET switches (suitably protected from flyback voltages) and drive it with a micro.

Jim

 

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Could be a reluctance motor.

No permanent magnet just shaped pole pieces