What determines the revs on a Brushless motor?

[Norman Adlam]

I've just got my first brushless controller (Phoenix 10) and, whilst waiting for my Hacker Brushless motor to arrive, tried it out on an old CDROM motor (ala. thread in EZone regarding CDROM motors etc).

Sure enough it works! :)

It looks like the revs are around 5k-ish, and this led me to think of what was the overall determining factor for revs on a brushless motor!

Is it numbers of poles? The wire diameter (so more current can be dumped, which might establish a magnetic field quicker etc)?

I think that the onboard processor is waiting for the motor at the moment, so I don't think it is the controller!

Any thoughts, guys?

Cheers,

[vintage1]

As far as I know its RPM per volt depending on the windings. As it reaches that the back EMF will block the incoming volts, reducing the current to the amount needed to overcome losses.

Fewere turns of thicker wire will reduce back EMF this getting more revs per volt.

At the upper limit, commutation of the controller will start to fail in the above 40kRPM range, and beyond that the thing will disintegrate anyway...:-)

The number of poles affects the torque I think. i.e. if you are energising a lot of poles simultaneously, you get more torque per amp as it were. So if you like a mulitipole motor is a bit like a geared three pole or whatever. Better efficiency at lower RPM.

If you want to get max efficiency use the very best magnets, and drop the windings down to something lower - and let it scream at 20k plus ;)