Hello,

Thanks for the comment, slotless motors are having veyr low inductances, so have you tried increasing PWM frequency to values like 40kHz and 60kHz and see how the behaviour changes? also pls try to reduce Current Controller Kp and Ki and see if that vibration gets better ( power recycle after changing these two gains needed)

Milad

Increasing the PWM frequency seemed to have no impact. I left it at 60 KHz.

Motor identification sets the Kp to approximately 0.9 and the Ki to approximately 0.008. I tried reducing them and it improved things a lot! The lowest I went was a Kp of 0.2 and a Ki of 0.002. This resulted in the following as shown on the performance monitor (under no load conditions):

For a setting of 800 RPM:

Minimum =   762  Maximum =   828  Average =  795

For a setting of 1080 RPM:

Minimum = 1063  Maximum = 1100  Average = 1081

The motion of the motor is now very smooth and quiet - just what I want. I will be using this to drive a DIY turntable platter, so I want it as smooth and quiet (and accurate) as possible. Obviously, I would prefer no variation, but I imagine that the inertia of the platter will filter this variation out. I can also reduce the diameter of the pulley that is mounted to the motor shaft, thereby being able to run the motor faster. The speeds of 800 and 1080 were based on a pulley diameter of 0.5 inches. I can probably go with a 0.25 inch pulley and double those speeds.

Are there any tradeoffs / drawbacks with reducing the Kp and Ki like this? Would it perform better if I went even lower and is there a lower limit I should not go below? I would have tried even lower, but I don't want to cause any problems for the motor or controller.

I really appreciate your help!

Hello Paul,

Thanks for the update, reducing the gains can cause the system to become slower in response, but as you experienced before, too high response rate also comes with its own perks, the idea is majorly to tune the system to have minimum Error and maximum performance per application, so the gains are completely dependant on your system, if you are happy with the performance while the machine is in use, then there's no worries.

Milad