Here's a simple example: six sizes of ball, and six pieces of track, each slightly different widths. Some balls fall through, some don't.
How to use this code: Click the code, press Control-C to copy it to your clipboard, then in Marble Run Maker hit
Here's an example of using it:
Remember, you can use and re-use any track profile you want. Pick the track whose profile you want, then hit
C (or click Option, Track, Capture Track Profile). Any track you draw now has this profile. You can also apply this profile to other tracks in the scene. Pick other tracks and hit
A (Option, Track, Apply).
rekindle command allows your contraptions to regenerate themselves as many times and as frequently as you want. Here are two examples: