Affordable brushless motors are great for a variety of motion applications, but often require a gearbox to tame their speed. Michael Rechtin decided to try his hand at designing a stackable planetary gearbox. For a brushless motor that allows him to add or remove stages to change the gear ratio.
The gearbox is designed for 3D-Printing around a cheap, 5010 size, 360 KV, sensorless motor from Amazon. Each stage consists of a 1:4 planetary gear set that can be connected to another stage. Or to an output hub. This means the output speed reduces by a factor of four for each added stage. Thanks to the high-pressure angle, straight-cut teeth, and fairly loose clearances, the gearbox is quite noisy.
To measure torque, Michael mounted the motor-gearbox combo to a piece of aluminum extrusion. And added a 100 mm moment arm to apply force to a load cell. The first test actually broke the moment arm, so a reinforced version was designed and printed. The motor was able to exert approximately 9.5 Nm through the gearbox. This number might not be accurate, since sensorless motors like this one can not provide a smooth output force at low speeds. As Michael suggests, adding a sensor and encoder would allow for better testing and low speed applications. Check it out in the video after the break.