Metal Micro Gear Motor speed variation

Some months ago I purchase two of the motors and encoders shown below. The motors drive a Mini Robot Cart i made, which has a Pi Zero and camera. All items work nicely.

But …
There is a 6.5% difference in the speed of the two motors. The encoders indicate one motor is turning faster than than the other. The slower motor also has more gear noise. Because the motors are geared so high the cart moves very slowly, which is what I was after, but it turns slightly as it moves requiring constant adjustment.

I have considered altering the speed of one motor to match the other using the encoder pulses to determine by how much.

Is this difference in speed normal, it is a little higher than what I would have expected.
Has anyone else experienced this …


An unfortunate reality of life. There’s really only two solutions:

  1. Mechanically lock them together (like a tank or bob cat, or

  2. Control them so they spin at the same speed.

If you opt for the second one you can either do it manually or automatically as you’ve already considered. If you just want them to match each other, I’d suggest running a PID controller on the faster drive so it just follows whatever the slower one is doing.

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