Square Tires on Circular Track

It is well known that square wheels can roll on a properly curved track. In this 3D print design, the square wheels ae designed to rotate around a circular track.

To print the model, you need to print the base track, rotating threaded arm, 2x pyramids, and 2x nuts. The rotating threaded arm needs to be printed with supports from the build plate – and these are easily removed after the fact. The other parts do not require supports.

Make sure the pyramid pieces spin freely after assembly. Depending on the quality of the print, you may wish to sand down the arms where the pyramids contact it to make sure this is smooth. I left generous tolerance between the parts – so this may be unnecessary. My print did not require any smoothing
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I printed this using PLA and there is insufficient friction between the PLA surfaces to make the rolling happen consistently. There are two solutions to this that work quite well. My preferred solution is to apply double stick tape on the track underneath where the pyramids are supposed to roll. The other option is to wrap a small rubber band on the outside of the pyramid so it can grip the track. In the second option – the rubber band increases the size of the square wheels and so loosen the nut a bit to allow the pyramid to move to a slightly larger radius from the center.
Hold the base in your hand and spin by pinching the opposing sides of the rotating arm and pressing down with slight pressure against the base.