Slopeless marble run for Lego bricks

This is a marble run for Lego bricks, designed for 14mm ball bearings.

The tracks are parametrically generated in OpenSCAD and are made up of five track types:

• Straight (flat)

• Straight (down)

• Curve

• Speed variation

• End piece

The marble run is designed to use no slopes that end up as staircases when 3D printed. Instead it uses rails with an increasing distance between them, so the marble runs down between the rails onto the next track.

Aside from this, most pieces should be self-explanatory except for the speed variation piece. This changes the rail distance without lowering the center of mass for the marble, which changes the ratio of translational and rotational energy. In other words: The marble slows down momentary and then returns to its original speed. Well, almost. Friction limits what can be achieved here and the effect is admittedly rather subtle. If you want to lean more about it, check out the video or blog post (https://there.oughta.be/a/lego-marble-run).

Because of the flat design, track pieces are easy to print without support and should work at any reasonable layer height.

I am providing the OpenSCAD file to generate customized pieces and as a generator for sites that support it. For convenience, you can also use the following packs:

Starter packs

• S (15 pieces)

• M (26 pieces)

• L (45 pieces)

Collections of different sized track pieces

• Straights flat (length 2-12 studs)

• Straights down (length 2-12 studs)

• Curves (length x width 2-8 studs)

• Speed variation (length 2-8 studs)

• End pieces (length x width 2-8 studs)

Note: I recommend to stick to pieces of up to 8 studs. Those are easier to handle, mix better with Lego pieces and you will have to battle warping for longer pieces.