I purchased 3 Pololu 37D 70:1 motors with encoder, initially, I heard 2 of them were making a “chopping” sound but I thought it was not much of an issue. Today, I ran some tests using a microcontroller using PWM to control motor speed along with a Pololu TB67H420FTG motor driver. I then realised that there seems to be an issue with those 2 motors as an oscillation appeared when using 2 of the motors. Here is a plot that shows this.
The 3rd motor works perfectly, is there possibly a defect with the motors?
The chopping sound (oscillation) still persists even when plugged directly into the power supply. It is not an issue with the PWM control, which works perfectly for the 3rd motor. I also tested without the motor gears and the issue still persists.