These were designed for my little lad. There are 4 different sized gears, the two larger ones (gear 3 and 4) have handles so that they can be easily spun round.
They use standard 608 skateboard bearings (available from amazon/eBay)
They also require 10x3mm Neodymium magnets again, available from online retailers.
All parts are press fit so probably best to use a vice, or simply warm up with a lighter and press them in place.
All parts were printed on a Creality Ender 3 with the following settings:
0.2mm Layer height
205/60 Degrees (PLA)
20mm/sec First layer - 50mm/sec rest of print
NO SUPPORTS NEEDED
Print as many as you like in all different colours - the more the merrier!
Side note - if you can get bearings with ceramic/glass balls inside, this would be better as the magnets do very slightly create resistance in the gears, but nothing that causes the parts to not work.