LEGO Micro motor
thingiverse
I'm going to give this a try. I am currently watching this video on YouTube: https://youtu.be/yLcMHgs7VZg. The motor used in this project is the same one found in a typical gearbox. You can find detailed instructions and design files for this project at Thingiverse, specifically with thing number 686321. I printed this model using my ToyRep printer. If you're interested in printing this project yourself, you can find the design files on Thingiverse under thing number 1113688.
Download Model from thingiverse
With this file you will be able to print LEGO Micro motor with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on LEGO Micro motor.