brushless and varying speed

[bartinla]

Hey everyone,

I am controlling a 12V brushless motor with Hall sensors. I am also using discret MOSFET drivers to get 24V on the top MOSFETs.  When starting everything goes well,  but when I reach a certain speed, the motor starts shaking. So I first thought that there was something wrong in the way the commutation was done, but the signals look really nice, except that they don't raise all the time anymore to 24V. So of course I thought then that it was due to the MOSFET drivers, and that the bootstrap capacitor didn't have time to recharge, then again the signals told me that I am wrong.

Finally I put my finger on the axis of the motor and it is then working perfectly... could someone explain me why the motor cannot work properly at full speed and without a load?

thanks in advance for your help

Gaetan

[AnalogKid2DigitalMan]

Is this a closed loop control? If so, sounds like the tuning (pole/zeroes) of the loop filter response may be out of tune.

Your power supply may also be reaching it's current limit and folding back the voltage.

Without much details posted to go off of, these are just a coupel wild guesses. Is there even any DAQ or NI motion control hardware involved?

Message Edited by AnalogKid2DigitalMan on 01-19-2007 07:29 AM