This model is a simple, cheap motor base for the fantastic Tulio marble run.
You can either download the original model and use the OpenSCAD file to re-generate the stl files, or I have included the updated stl files if you don't have OpenSCAD, or can't be bothered :)
The motor is a ga12-n20 (Search Google for suppliers. Amazon has quick delivery but expensive. AliExpress has cheap but takes a while to arrive). In the video I used a 6V 200rpm motor but it will run slower since I am only supplying 3V. I think a slower motor might be better since with this fast motor the marbles tend to 'catch up' with the slowest one over time. The motor should be a 3mm shaft variant. The positive battery terminal should go to the motor -ve so that the screw turns the correct direction.
The motor coupler is a D slot, so just be careful when pushing it on to the motor. The top of the motor should end up flat with the top surface of the base.
For the battery contacts I used a spring bought at Home Depot, cut it in half and bent out part of the spring to allow it to be pushed down into the battery spring mounting groove. The non-spring end is just pretty much anything you have lying around that can be soldered to. I used a cut and straightened hose clamp.
The power switch again is just what I had hanging around. I clipped off all but 2 contacts. You might need to modify the base model if you can't find a switch that is about the same size.
Solder each motor connection to one of the cut springs then insert the bent out part into the narrow slot in the battery holder to keep it in place. The switch should have each of 2 terminals wired to one of the flat connectors which have been inserted into the narrow slots too. With my switch I was able to simply bridge each terminal to one of the battery connector strips. Make sure to use the correct terminals on the switch, i.e. terminals that short when the switch is 'on' and are open when the switch is 'off'. Batteries can then simply be inserted in opposite directions.
If you have already printed the main track then you will need to cut out a hole in the bottom to allow the spiral to completely drop through the bottom (or at least allow the coupler to fit through the hole. I found it easier to assemble with the hole completely open, but it might be OK smaller just for the coupler. Note the screw is modified and should be aligned with the smaller triangle to the motor and the original cap opening to the top. I spent about 20 minutes trying to work out why balls weren't getting pulled up only to realize I had flipped the screw upside down. It is designed specifically to take in at one end and spit out at the other :)
The base is customizable and the holes in the base can be changed. I liked circles but setting the number of sides to 3, 4, 5, 6, 7 or 8 all look cool too.