298:1 Gearmotors Variation

298:1 Micro Metal Gearmotor HP

I need these High Torque motor so my small robot can climb up reasonable slopes.
but… I bought 10 of them and they are RADICALLY different. The no load speed can vary ± 30%.
As in - one rotates 4 times in the time it takes the other one to rotate 3 times.

I was expecting there to be some variation, but 30% is enormous!
Anybody else have similiar problems and have some advice?
Are the Pololu products typically this off spec?


I would not expect an RPM variation of 30% for these motors. Are they all very different, or is just one different? One thing you can check right away is that the gearboxes on the motors all look the same. If the gears look different, you might have motors with different gear ratios.

Also, what voltage were you running these motors at? When you tested the motors were they all being powered from the same power supply? A variation in supply voltage can definitely lead to a variation in RPM.

- Ryan