Motor in non-linear magnetic field

J

Thread Starter

j. daniels

Hello,

I'm having some issues with a motor controller. I have a brushed motor but one different part is that for operation the motor sits in a magnetic field which is external to the motor housing. The field in which it sits is 1.5T, but what I think might be one issue is that the field varies from 1.6T on one side of the motor to 1.4T on the other side. The controller is a PID set up with a locked anti-phase pwm into the H-bridge. The problem is that when I attempt to run in this configuration the motor will move at slow command speeds. As the command increases it eventually starts to turn but is very bumpy/choppy. At high speeds it will run smoothly. So it appears that the motor is fighting itself at low speeds.

I have put the motor in a linear, but much lower (0.4T) magnetic field, an it operates as expected. The motor will also operate smoothly over all speeds with straight DC (not pwm) applied, or using sign magnitude pwm. The magnetic gradient cannot be changed and I would rather keep the locked anti-phase configuration as sign magnitude creates a number of other issues.

Sooo... does the gradient issue hold any water? Is there something with the locked anti-phase configuration I might be missing. I realize it's an oddball problem but any thoughts would be appreciated.

Thanks,

jack
jd710 @ hotmail. com
 
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