3-phase BLDC motor driving frequency formula

[daveatol]

Hi all,

I found some 3 phase motors on scrap and was wondering how to work out the rotation speed based on the drive frequency. The motor has 63 coils and 56 magnets.. does anyone know the formula to calculate the number of electrical cycles to attain a mechanical cycle?

Also, just showing my ignorance, but what stops an RC ESC being used to drive a larger motor? Is it just the rotation speed? e.g. could a 60A, 25V ESC http://www.ebay.com.au/itm/160631159669 be used to drive a 24V BLDC motor?

Thanks.

PS I did ask this on another forum a week back but couldn't get the answers I was after.

[peter.mitchell]

generally, RC based ESCs have a pretty tight frequency range, designed for 2-4-6 pole motors, if you use them on a high pole motor the motor won't spin very fast and the ESC may not be able to accurately judge the position of the rotor form the back EMF.

Also, to a certain extent, on BLDC motors, the "voltage" doesn't matter; provided you don't overload the motor or go outside its RPM range, it will most likely be fine

[daveatol]

Thanks for the reply Peter. So the problem may be with the drive frequency and feedback at low RPM.

Would you happen to know how to calculate the RPM from the number of coil triplets and magnet pole pairs?