Hi Bob
If is better to run them at there rated current. If they are overdriven the excess heat can eventually damage the motor. Also you will get better speed performance by not overdriving them.
Do the motors have any markings on them as you may be able to determine the rated current from that?
Also what is the length of the motor body? That will determine if it is a single or double stack motor.
The shorter single stack motors don’t usually draw more than 2.8A. So that may help.
Consider using a set of these DB-9 breakout boards. They allow you to easily set the current without having to solder in resistors as they have an inbuilt adjustable potentiometer.
https://www.homanndesigns.com/index....roducts_id=111
Cheers
Peter
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