Here is a 3D printed marble machine with a feed screw that brings the marbles to the top without a simple turn. It has 3 different tracks to the bottom. Two of the tracks are connected, so marbles will alternate between them. The design is by MRoek on Thingiverse.
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The Cyclone: 3D Printed Marble Machine ★ Gadgetify
The Cyclone marble machine is 3D printed in PLA. It is made for 8mm steel balls.
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