This N20 Micro Gear Motor With Encoder is intended for use at 12V. Though in general, these kinds of motors can run at voltages above and below this nominal voltage; so they should comfortably operate in the 3 12 V range (rotation can start at voltages as low as 0.5 V).
Lower voltages might not be practical, and higher voltages could start negatively affecting the life of the motor. The micro metal gear motors are available in a wide range of gear ratiosfrom 5:1 up to 1000:1. Except 1000:1 gear ratio versions, all of the micro metal gear motors have the same physical dimensions; so one version can be easily swapped for another if your design requirements change.
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