I just saw https://www.youtube.com/watch?v=4gkbb2CBzQI and decided to make one to play with and evaluate.

See it in action : https://www.youtube.com/watch?v=fnSvYcbAfJw

It has herringbone teeth.

The first stage has

"ring_teeth", 50 "sun_teeth", 18 "planet_teeth", 16 while the second stage has

"ring_teeth", 51 "sun_teeth", 17 "planet_teeth", 17

The model is parametric in openscad so you can customize it easily, build upon the PolyGear library https://github.com/dpellegr/PolyGear

Just edit splitRingPlanetary.scad to customize it.

You can use for the second stage ring_teeth+k,sun_teeth-k in the splitRingPlanetary.scad to obtain various ratios ; the same k must be used so that the top and bottom stage planet share the same center.

If you want to be able to replicate what Levi Janssen did, you can use badSplitRingPlanetary.scad which allows to remove the standard parity constraint on the number of teeth for a planetary drive. (In theory the sun on the second stage violate one geometrical constraint, so there is a flag to remove it).

The file badSplitRingPlanetary.stl does have tighter backlash, a sun and same number of planet teeth on both stages and works fine therefore it has an even bigger reduction ratio.

First stage : "ring_teeth", 50 "sun_teeth", 18 "planet_teeth", 16

Second stage : "ring_teeth", 51 "sun_teeth", 17 "planet_teeth", 16

The openscad needs roughly 8GB of RAM to render the STL.

I have updated the model to make it easier to print. And I've printed it successfully.