Summary

This is #35 from "Five Hundred and Seven Mechanical Movements" by Henry T. Brown.
http://507movements.com/mm_035.html

Instructions

Creating proper elliptic gears is quite sophisticated. I did something like a workaround: I created two gears, sliced and merged them into one. It works fine, but I would not build it into a real gearbox because of the poor efficiency.

You will need a screw M6 by 10mm for fixing the small Gear.
If you scale down

to 66%: a M4 by 6mm should work
to 50%: a M3 by 5mm.

And finally you need a rubber band for the Wedge and Base.

Preview in SketchFab:
http://skfb.ly/5k3ecba

SketchUp model:
sketchup.google.com/3dwarehouse/details?mid=ef3699d62dd4c5f041f50478f7943c0a

Elliptic Gear