These tracks are designed to work with a 25mm diameter marble. For best results, use a glass marble, but there is an stl included for a marble which you can print with supports and I used 50% fill for a bit more weight. You can print all of these models (except the marble) in PLA without needing any supports. The curved tracks may require minimal trimming and light sanding can help with speed and reliability, but the level tracks should work without any tidying up. The tracks are designed to snap together with plenty of space to allow for imperfect printing. The tracks are designed to fit on to duplo blocks, but very snugly, as I went for stability over ease of connection there. So with the short/up/down and loop tracks you'll need to push them on to duplo blocks with some force. The long straights and long curves are not as tight, and the helix tracks need to be loosely supported in some other way. You'll need to experiment a lot with various configurations to get the right speeds to pull off the loop and helix reliably, but that's part of the fun! To make a single layer of the helix you can use: - 1x helixStart.stl - 8x helix.stl - 1x helixEnd.stl To make a loop, you can use: - Approx 2x down.stl at the top - Approx 3x straight.stl - 1x up.stl - 8x loop.stl - 1x up.stl - some straights and ups to slow it down after The loop needs to be held solidly in place, as too much wobble can make it unreliable. You can lock the bottom two loop tracks in place with duplo. Also, you could probably print everything at 50% scale and use a 12.5mm marble, and lego for supports. Enjoy!