Air gap problem in hub motor

[arjun]

Hello,
I have a chinese controller of 35A having function of self tuning. And i have made 2 BLDC hub motors A & B having following parameters:-
MOTOR A
No. of poles- 52
No. of slots- 48
Stack length - 30mm
No. of parallel strands- 10
No. of turns - 7
Air gap- 0.6mm
Wire gauge - 24 swg


MOTOR B
No. of poles - 52
No. of slots - 48
Stack length - 30mm
No. of parallel strands- 10
No. of turns - 7
Air gap- 0.2mm
Wire gauge - 24 swg



Now, when I connect motor A to controller ,and self tune it, it works perfectly without any humming noise and low current. But as soon as I connect Motor B with the same controller, and self tune it, there is humming noise (this happens when self tuning is not done properly). Only change in both motor is of air gap, every other parameter is same.


Initially I thought there might be problem with controller. So to check it, I wound another 2 motor with 6 turns , other parameters being same. Now, there was no problem with self tuning and both motors works perfectly with same previous controller.

Can anybody tell me why there is problem with self tuning when there are 7 turns with low air gap. And not with 6 turns??

 

[fechter]

Just a wild guess: with the smaller gap, there will be a higher cogging force and the self-learn function may not be putting out enough current to overcome the cogging. Tune it with the big gap motor, then change motors without re-tuning the new motor and see if the motor runs OK.
Another possibility is the smaller gap motor has another problem, like a bad hall sensor signal.

 

[arjun]

Just a wild guess: with the smaller gap, there will be a higher cogging force and the self-learn function may not be putting out enough current to overcome the cogging. Tune it with the big gap motor, then change motors without re-tuning the new motor and see if the motor runs OK.
Another possibility is the smaller gap motor has another problem, like a bad hall sensor signal.

If problem is with smaller air gap than why is 6 turns winding self tune properly in smaller air gap. But 7 turns does not.
Is it possible that with 7 turns magnetic flux generated is more than permanent magnet flux and due to this sensor is not able to get proper signal during self tune??