Stackable Heavy Duty Coaxial Planetary Gearbox

I designed this gearbox for actual mechanical applications, so quite a few bearings are used.

I don't have actual photos available right now, but I build a two-stage version printed with regular PLA that runs at fairly high input speeds (~ 3000 rpm) with no problems using tea light wax as a lubricant for the gears.

The included input pulley is designed to provide some airflow for cooling.

In theory, you can stack as many stages as you like. Each has a gear ratio of 4.4(05286344 to be exact).

The gears are helical so the gearbox runs very smooth with low backlash. To change the helical direction, simply mirror all geard parts in the slicer.

Optionally, you can use a 8 mm shaft as a coaxial output, so the input and output can be on the same side of the gearbox. In this case, you should provide some of the sun gears with 8x12x3.5 mm (flange) bearings for stability.

One stage fits easily on a i3 print bed. There are only a few parts that need some support and everything is very easy to print.

To connect multiple stages, m5 threaded rods of appropriate length with nuts on both ends are used.

Also needed for each stage:

•  three m3 or m2.5 15 mm spacers (to connect carrier halves) 
•  six m3 or m2.5 12 mm countersunk screws (to connect carrier halves) (other lengths might be suitable)
• three m3 28 mm countersunk screws (axels for the planet gears) (other lengths might be suitable)
• three m3 (lock) nuts
• six (three are enough) m3 16 mm countersunk screws (to connect sun gears to carrier) (shorter lengths might be suitable)
• six flange bearings 3x8x3 mm
• two bearings 50x65x7 mm
• one bearing 25x32x4 mm

Realizing, the 15mm spacers might be a bit annoying to source, I added a STL for a printable m3 spacer and a third option for the primary side carrier which uses three m3 28mm screws and nuts instead of the standard six shorter bolts that would screw halfway into the spacers from each side.