Ball Track Spinner

- a spinner design I wanted to try based on D13mm steel balls
- balls can run freely inside their tracks, will go to outmost position during high rotation speeds
- kind of mini marble run during slow rotation
- added revolving grooves for better haptic feel
- needs 1x 608 skate ball bearing and 3x D13mm steel balls
- bearing will need to be fixed with a bit of glue
- added first test version with straight tracks in files (V2)
- model units are [mm]

***EDIT 09.06.2017*** new stl model added:
- "_inch" for 1/2" (12.7mm) balls (untested)

***EDIT 05.01.2018*** new stl model added:
- "_8mm for 8mm balls (untested)