Originally posted by synapse79
I have a question. Do brushless motors run on DC or AC?
Well, it starts to get a little sticky depending on how you define it, but basically I think the answer to your question is essentially AC, using the term rather loosely.
A regular brushed motor is clearly DC. At full throttle the controller just feeds a steady voltage to the motor. To run slower, the controller turns that DC voltage on and off - the more on vs. off, the faster it goes.
A brushless motor is a whole 'nother matter. I don't know exactly how it works, but the controller essentially 'turns on' one pair of the three power wires at any given time. I believe it also uses all combinations of 2 wires out of three, depending on which wind it wants to excite, which depends on where in the rotation the rotor is located.
So each pair is excited once each revolution, I think. So the controller has to switch the power on and off to each pair pretty rapidly. At 25000 RPM, the controller would have to switch something like 75000 times. That's a whole lot faster than a brushed controller would be switching at any speed. This is probably the key reason why the Novak controller gets so hot - switching consumes power.
And this brings up the real trick of brushless motors - the controller needs to know where the rotor is in order to know which wind to fire. That's why the Novak has sensors - they detect the location of the rotor. This also explains cogging - if the controller is a little confused about where the rotor is located, then it could fire the wrong wind and the motor will not run very smoothly, which is cogging. The older generation of brushless motors even occasionally started off the line going backwards because the controller wasn't sure where the rotor is. All the new generation brushless controllers seem to have this pretty well figured out, even the sensorless ones.
I may be a little off on the details, but I believe this should give a basic idea of what's going on with a brushless motor.