@phoenixengr - Mark Kelly had two very unique designs for open loop controllers, the brushed DC controller being one of them. The other was the Synchrotron AC-1, which was an open loop controller for synchronous AC motors. That controller was the most accurate open loop motor controller I’ve ever used, and every conceivable motor parameter (frequency, amplitude, phase angle, harmonic distortion, etc) could be adjusted. This level of parametric adjustment allowed cogging to become nearly non-existent.
I still own both.
I still own both.