This awe inspiring geometry is known as a sphericon. It has a single continuous surface that makes it roll along a very curious wobbly path. This is my simplified 'retro' variation. It has shallow grooves that are fun to decorate.
Download includes a split version optimized for FDM printing. The center connector piece may need to be scaled down 1 or 2 percent depending on your printer... or you can just glue the halves together using E6000 adhesive or similar. Print 2 identical halves, just offset 60 degrees when you stick them together.
This can be printed with a 5% infill, but the heavier it is, the better it tends to roll, so a solid copperfill version would be pretttty cool ;)
Scale however you'd like
Pictured model printed in MatterHackers White PRO PLA