This is an early prototype version. I have created an improved and more advanced version which can be purchased here: https://redpah.com/product/221/deskorbe
Mechanical design, outer casing rotates three separate bevel gears to cause the inside geometries to rotate in the opposite direction. This is my first design, printable as a single working part, no assembly needed.
Simply print and remove the support material, no assembly required. The bottom gears may initially stick due to unexpected melting of the plastic, but this can be easily fixed by pressing up on the gears.