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Finding out Micromotor gear ratios



As part of a past project we were left with a lot of Micro Metal Gearmotors of which we don’t know anything about.

We have started trying to identify the Micromotors gear ratios by using a mini encoder (https://www.pololu.com/product/1217) and applying 6V directly to them to find out the RPM on the outer shaft. However, we are still getting some motors that don’t really fall in any of the RPM categories of the Micromotor specification table (https://www.pololu.com/category/60/micro-metal-gearmotors), for example we have found one that reads 868 RPM in average and we don’t really know whether to classify it as a 730 RPM or as a 1000 RPM motor.

Is there a better or simpler way to find out what is the gear ratio of each of the motors?

Thank you,



When you are running the motor it might be good to keep in mind that the wheel with the encoder adds a little load to the motors, so they will not be running at full free run speed. If you have any order information and you email us at support@pololu.com with that information, we might be able to tell you more about which gearmotor you have. Otherwise you can use some of the physical characteristic to narrow down the possibilities. For example, the motor leads and back of the motors are a bit different between the carbon brush and precious metal motors. Here is a picture where you can see the motors side by side:

Also, in this forum thread Derrill explains how you can tell the difference between the HP, MP, and LP micro metal gearmotors (precious metal).




Thank you, I am going to check the motor leads, unfortunately we don’t have any order information left from the project.