ORIGINAL: Argess
Access: You had mentioned mentioned about plotting the current for one of these motors so we can see what an ESC puts out. I think the question I have is, what does the ESC do during the time a a pole shold be energized....say for 120 Deg of rotation. Can you describe it with out going to too much trouble? Is it just "ON", or does it pulse the pole?
Once you get near holding full throttle (ie. what's happening with that dyno), it's just holding the pole on for that phase. Then the next 120 degrees, it switches to a new pole, and so on. That's partly why, as the RPMs increase, the current drawn decreases. From ~106A to ~10A with the dyno test link above. If full throttle is not being held, then it is pulsing to limit power. When the coil isn't 'in phase', it's being switched not to an open circuit (this was a mistake in the schematic above), but to ground.
I'd say this is why the efficiency at the lower RPMs is so bad. I think you could get almost as much current, hence torque, at the lower RPMs if you turn that switch on at only, say, 25% duty cycle or 50% duty cycle. I don't know if this is going to make sense to anyone other than me, but, if you normalize the phase: At low RPM, when voltage is applied, the rate of current increase is high, and when voltage is no longer applied, the rate of current decrease is low. At high RPM, when voltage is applied, the rate of current increase is low, when voltage is no longer applied, the rate of current decrease is high. This means that even with 50% duty cycle at the lower RPM, you can still get a good deal of torque (more than 50%). The rate of current increase (and decrease) is based on both the impedance of the coil, and the back-EMF from the spinning rotor.