"Twin Tops" is my rendition of Grand Illusions "Magneturn" (grand-illusions.com). Spinning either top induces motion into the remaining top thanks to magnetics. The design also minimizes rotational friction via opposing magnetics between the Base tower tops and each Top. As combined these features create a great magnetics educational tool. My rendition is larger than the original to make it more "grandkid friendly" (easier to grasp, more difficult to swallow).
You will need to purchase 10 neodymium disk magnets 12mm in diameter and 3mm thick in order to complete "Twin Tops". I have purchased these magnets from a local hardware store (Ace) and online (Amazon).
Designed using Fusion 360, sliced using Cura 2.3.1, and printed on an Ultimaker 3 Extended.
Step 1: Print the Parts.
Print two "Top.stl", and one "Base.stl", in the colors of your choice.
I printed the parts at .1mm resolution with 50% infill, but to save time and plastic, .2mm and 20% should work fine.
In order to minimize warping when printing large flat parts such as "Base.stl", if you have a heated build plate (as do I), remove the build plate from the printer then thoroughly wash it with a degreasing dish washing detergent (I use Dawn) in hot water to remove any residual fingerprint smudges. Once dried, carefully examine the build plate surface for any residual print material build up and if found remove it with a safety razor and repeat the wash cycle. When completely cleaned and dried, re-install the build plate then perform the build plate leveling procedure being very careful to not touch the build plate surface.
In order to minimize warping when printing large flat parts such as "Base.stl" on non-heated build plates, start by removing the build plate from the printer then remove the old painters tape (if you use it). Next clean and dry the build plate as previously described. Finally, carefully install fresh blue painters tape (I recommend using it), then re-install the build plate and level it.
And finally, using either a heated or non-heated build plate, if your printer has a raft option, use it for large prints. While it does increase the print time and uses slightly more plastic, a raft will minimize warping and almost eliminate the first layer "oozing".
Step 2: Prepare Your Magnets.
As noted, you will need to purchase 10 neodymium disk magnets 12mm in diameter and 3mm thick.
In order to correctly orient the magnets in the printed parts, I started by stacking all 10 magnets together, then one by one I placed an "X" on the topmost magnet using an indelible ink pen, then slid that magnet off the stack, and repeated the process with the subsequent magnets until all 10 magnets were marked.
Step 3: Install Base Magnets.
Press the Base "tower" magnets into the base towers with the "X" facing upward.
Step 4: Install Top Magnets.
Press the Top "arm" magnets into the 6 arms of the two Tops with the "X" facing outward. I used slip joint pliers to press these magnets into position.
Press the Top "center" magnets into the inside center of the two Tops with the "X" facing downward (the "X" must be visible when looking into the inside center of the Top). I used an 8mm deep socket to press these magnets into position.
Step 5: Place Tops on Base.
Slide the two Tops into position on the Base towers.
You should now be able to spin either top and examine the reaction of the remaining top. Try differing speeds and directions and notice the reaction. Also, with just one top in position on the base, notice how long it spins thanks to the magnetic repulsion between the Base tower magnet and the top center magnet.
I hope you enjoy it!