fischertechnik ball wheel

A ball wheel (caster wheel) block for the [fischertechnik](https://www.fischertechnik.de/en) construction toy system. Needs a [steel ball](https://ft-datenbank.de/ft-article/2866) as included in the fischertechnik marble run line with a diameter of 12.66mm.

The ball wheel block is meant to be used in turtle like robots as a third wheel with 360° freedom of movement. It's height with ball inserted is 15 mm. Make sure to clean out any excess filament to allow as little friction as possible.