casainho wrote:walls99, could you please tell me if you think the motor could work (with load, like on a bicycle wheel, starting from 0 velocity) only with current feed-back and not BEMF?
I got my motor running but without BEMF.
I made some simple but interesting tests.
With 15% duty-cycle and 10ms the motor were running very slow (about 12 RPMs, motor Cute85 for 20'' wheel). But I were using the variable power supply and I could change the power applied to motor by defining the voltage supply.
(Case 1) I found that with a lower voltage, like say 15V, the motor don't turn or vibrates/makes noise/small turns. (Case 2) If I rise slow the voltage it starts to turn up to a velocity which seems to be perfect (but slow due to the 10ms), no noise, no vibrations. But if I brake the motor with the hand, it starts to vibrate/make noise and stops...
(Case 3) Continuing, if I rise the voltage (without braking the motor with my hand) the motor starts vibrating/making noise again but this time rising also the current/power used!!! Then I tried to brake and it stopped to make noise/vibrations but the current still high. I had a bit difficult to brake and stop the motor. I rise again the voltage and keeping brake the motor, until I found I couldn't no more brake it!! it turns with strong power, no vibrations nor noise.
It looks like you are running in open loop, so this is the expected behaviour. This mode of operation is not really usable as you can't control timing or torque, however it's a good 1st step to understand brushless motor control
BEMF sensing/timing and close loop control is the logical next step but it's also more complicated. Using only current feedback is possible but a lot more complicated, see FOC theory.