I couldn't find a 3d printed ball reducer so I finally figured out how to make one.
+s to open sketches and add ins. I use vs code to run it.
Main params should be edited. You can use this visualizer to play around with them for a preview https://github.com/Tomato1107/Cycloidal-Drive-Animation 
Running the script produces 3 sketches; balls, eccentric moving track , fixed track
sketch 1: the balls
sketch 2: the moving eccentric disk
I used the center spline for the path for a sweep. this creates the ball track.
You also likely need to add a ball bearing cage like this:
it is pretty much impossible to operate without this
Stl files can be found here: https://www.thingiverse.com/thing:5413119
video here: https://youtu.be/AjoCcUVM0n8