Gearbox with adjustable ratios

thingiverse

I had a need to move slowly a pinion gear on a rack. Using a DC motor controller with my small hobby motors to lower the RPM, I had to give up some torque. A gearbox was the solution. This is a generic but customizable gearbox, that exposes (via arcs in its face) two sides of the "driving" gear so that you can "engage" your motor. Your motor can be attached via your bracket (that you print), through the mounting holes on the faces. A bracket for a "DC 3-12V Gearmotor for ARDUINO Robot Smart Car" has been included. https://www.youtube.com/watch?v=nSY02jBna0w Instructions Materials: 8 off 4G x 9mm self-tapping button head screws. 2 off 2mm wires 25mm long (thin coat-hanger wire). 2 off 608 skate bearings (OD 22mm, ID 8mm, W 7mm). Print one of each face. Print 4 of 16.5mm spacers. Print one axle. Print one of each bearing spacer. Print 2 of 4.5mm gear spacers. Print 3 of 1mm gear spacers. Print 1 of keyed single gear. Print 3 of double gears. Print 1 of MotorGear. Optional: Print 1 of Motor bracket (if the included one does not suit, design and print your own). Optional: hardware for mounting motor to bracket (2 x 25mm M3 screw and nut for 1 supplied). Assembling the gearbox: Drill "out" the 2mm holes in the faces, gear spacers, and gears. Lightly file the rough print surface on all parts. Put a dab of petroleum jelly/grease on touching surfaces. Press 1 off skate bearing into each face, flush with non-bed surface of print. Press 2 off 2mm wires into 2mm holes in rough side of square face. Fasten 1 off 16.5mm spacer in each corner with 1 off 4G x 9mm screws. The spacers will be on the same side as the wires. Position face with wires up, and bearing to the top on a flat surface. Insert 1mm gear spacer on right-side wire. Insert double gear on right-side wire, small gear down. Insert 4.5mm gear spacer on left-side wire. Insert double gear on left-side wire, small gear down, meshing gears of left side. Adjusting ratios with supplied parts: Remove or add pairs of double gears. Create new corner spacers to new width using CornerSpacerMM.dxf (extruded). Print 4 corner spacers. Replace 2mm wires with ones adjusted to new width. Assemble as above. Adjusting ratios with custom parts: Work out desired configuration with paired gears, keyed gear, and motor gear needing to match tooth specs. Print paired gears with large gear extruded 3mm, the small gear extruded a further 4mm, and 2mm central hole cut. Print keyed gear at 3mm extrusion and the axle vector (smallest curve in MotorGearMM.dxf) cut central. Print the motor gear with the gear extruded 3mm to suit your motor (DXF included as a guide). Treating the bearing hole as fixed work out new positions of new 2mm wire holes. Print both faces using the supplied DXF's extruded to 5mm. The 2mm wire holes will need to be moved to the new layout (#4). Assemble as above.