I wanted to play with a Gravitrax funnel having a small/medium size. I decided to design this piece.
Ring connector is taken from: https://www.thingiverse.com/thing:3510861
The funnel works well. You would like to apply sanding to let the surface be smooth and adapt the slope.
Extra grey spacers on the right can be put in place should you decide to send to the funnel many marbles all together (to avoid unabalancing).

Funnel can be used as is (with the ring connector on one of the transparent plates letting the marble fall down) on inserted on top of this support I created for it: https://www.thingiverse.com/thing:5358423.

Video here: https://www.youtube.com/watch?v=mXCkNnEmhEI

Hope you enjoy.

Artillery Genius