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This is a small version of Triple Gear, also including an axle. Note that the video here does not show the axle.
In this unusual mechanism three gears mesh together in pairs, and yet they can turn!
If you take three ordinary gears and put them together so that each gear meshes with the other two, then none of the gears can turn because neighbouring gears must turn in opposite directions. Triple gear avoids this problem by having the three "gears" arranged like linked rings - the gears then rotate along skew axes, and the opposite direction rule no longer applies (although see also Oskar van Deventer's Magic Gears for another possible solution).
This is joint work with Saul Schleimer. We were inspired by another of Oskar's designs, his Knotted Gear, which consists of two linked rings that gear with each other, and of course we wondered if it would be possible to do three linked rings!
A note on materials: I have so far printed it in White Strong & Flexible, and Strong & Flexible Polished. It may arrive with the rings slightly fused together, but gently moving them back and forth will loosen them up, and the mechanism gets smoother with use. The polished and dyed versions seem to work fine as well, and may require less working in. I haven't tested any of the "frosted detail" materials, but I imagine that they should work fine. It isn't printable in the other "detail" materials because of cleaning problems.
Here is a video showing how to loosen the gears if they arrive somewhat fused together.