Magnetic gear spinner

A spinner with magnetic gears!

Hardware required

• 18 neodymium magnets (diameter 5 mm, height 2 mm) 

• 9 M4x20 steel screws. I used pan-head pozi-drive. Other heads may work, but the total length must be 23 mm.

Printing

I used PLA and 15% gyroid infill.

You will need to print the following, in any colours you like. Use 0.20 mm layers except where shown. 

• 2x endpiece (blue)  

• rod (black) 

• primary (green) - 0.10 mm layers

• modulator (purple) - 0.10 mm layers

• secondary (red) - 0.10 mm layers

• spacers (white)

Print the central rod first.

The primary, modulator and secondary contain bearings and MUST be printed with 0.10 mm layers. Use the rod to free the bearings as soon as possible after printing. Once the bearings are loose, a squirt of WD-40 will help them run more smoothly.

Assembly

Place the square rod into the first endpiece.

Insert 6 of the magnets into the holes in the primary, making sure that they have the SAME polarity. The fit is designed to be EXTREMELY tight - I suggest using a vice to squeeze the magnets in.

Place the primary onto the rod.

Screw the 9 screws all the way into the modulator (the large central part). I put the screw heads nearest to the primary, but the orientation probably doesn't matter. The screw should be fully contained in the modulator.

Add spacers as required to ensure that the magnet does NOT touch the screw head when the modulator is added. You WILL need to experiment with this! (To help identification, the spacers have a square notch for each mm of width and a triangular notch for each 0.1 mm.)

Check the polarity of the remaining 12 magnets BEFORE inserting them into the secondary in the same way as above. They should be attracted (via the screw) to the magnets in the primary.

Again add spacers to keep a gap between the end of the screw and the magnets in the secondary. 

Then put the second endpiece onto the rod. If there's any gap on the rod, you could add spacers to fill it, or you could resize the rod in your slicer. If it's not long enough, again resize it.

Finally spin it! There are six gear ratios, depending on which gear you hold - see below.

Acknowledgements

The design uses the wonderful printable ball bearing by Beavertank and the knurled surface is made using Ak-Adventurer's OpenSCAD library. Many thanks to both!

The magnets were from www.magnetstore.co.uk.

Magnetic gears are described at https://en.wikipedia.org/wiki/Magnetic_gear.

Inspiration came from this video. I also used https://3dprinteracademy.com/products/magnetic-planetary-gear-simulator-html-browser-app - a free-to-download HTML app to visualise the gearing and calculate the gear ratios shown below.

Gear Ratios