This is a planetary gearbox for use with 130 size, 3v dc motor. The gear ratio is 1 : 15.5. Print 3 copies of the gear9 as the planet gears.
The 5 holes in the support are to be tapped for 3mm screw. 4 screws secure the annulus part, and the central screw (30mm length) become the axle for the sun gear and the wheel.
The central holes in the gears and the wheel are 3.2mm diameter by design, they should allow an 3mm screw freely rotating inside but I still need to drill clean the holes with 3mm bit due to z axis wobble on my printer. The 3 other holes on the wheel are to be tapped for 3mm screws (10mm length) too, for the planets' axles.
I used a rubber band cut from a bicycle inner tube as the tire. I made this design for a mini sumo robot (10cm x 10cm limit). Maybe the gear ratio is too low but I will give it a try.
Use wheel2 for use with 36mm i.d. x 3mm o-ring tire.