I have designed and printed a collection of add-ons and spare parts for the Hape marble run Quadrilla. Have fun with it!
This is a small tower to be placed at the end of a track where the marbles should move downwards but sometimes don’t, because there are too fast and run beyond the hole.
Edit 25.01.2018: I did some minimal changes to the hole diameter and position, because I realised, that on some wooden tracks the marbles could get stuck.
Print upside down, like shown in the picture.