, we spoke about direct drive torque ripple, and how we need to constantly adjust the driving current to compensate for the imperfections that exist in any motor. We also need to periodically check on our direct drive motor to make sure it's still rotating at the prescribed speed, right?
This appears to rule out what the specialists call "open loop motor control
"—the way to run a motor by feeding it appropriate current, and simply ignoring whatever data might be given back on what the motor is actually doing. This is how most belt and idler drive motors operate.
The opposite of open loop control is "closed loop motor control
"—a type of control that considers the feedback of motor signals like current and position. As far as I know, all historic and current turntable DD motors use closed loop control. The deviation from an ideal is measured and is used to correct the speed in a negative feedback loop.