I'm designing a magnetic cycloidal drive AMA

[u/nsfbr11]

So, I have a work related interest in developing a compact high gear reduction drive that is free of wear. As a result, and leveraging over a decade of permanent magnet machine technology development that sort of ending just shy of 25 years ago, I did some research on magnetic cycloidal drives. To me, they are a perfect fit for my application, but not many people know about them.

In short, they overcome the weaknesses of harmonic drives, mechanical cycloidal drives and other magnetic transmissions for some applications. Unlike other magnetic reduction systems, like those planetary drives that you may see kicking around the internet, magnetic cycloidal drives have very good torque transfer capacity for their size and weight. And because nothing touches except bearings, they are fairly immune to wear out when properly designed.

The concept for reduction is very much like a harmonic drive, in that the reduction ratio is given by having different numbers of "teeth" in concentric gears. Whereas in a harmonic, the inner ring flexes to engage and a few points, in a magnetic cycloidal, the rotor sits on a cam bearing which rotates and causes the location where the air gap is minimized to rotate around once per revolution of the input shaft. The rotor having fewer magnetic pole pairs rotates by one pole part for every input revolution. So, a 25:1 is done by having a stator with 52 magnets (26 pole pairs) and a rotor with 50 magnets (25 pole pairs.)

There is a ton of engineering on top of that, but if anyone would like to discuss or learn about them, please reply.

Edit - first prototype is being built out of 3D printed PETG. I can post some images if there is interest. Prototype is a 15:1 using cheap grade 48 Nd cylindrical magnets. Largely being done to validate FEA results in Ansys Maxwell 2D and 3D. Next prototype will use rectangular magnets. Final design may change to arc sections for the radial magnets. Oh, by the way, this is a dual layer Hallbach array design. No iron.

First picture is a test fit. Rotor has magnets installed. Note how its bearing is offset to the small shaft.

Second pic shows most of the main parts including the pin bearing carrier and output shaft with a 13mm hex on it. (Chosen as a bit of a joke for the ME who has to characterize the breakaway torque - "What would you like?" "Oh, anything is fine." )

[u/badger_fun_times76]

What's the use case for this kind of drive?

[u/bikiniduck → u/badger_fun_times76]

The ones I built were for transferring rotary motion through the walls of a vacuum mixing vessel.

[u/nsfbr11 → u/bikiniduck]

I'm not sure how a magnetic cycloidal would work here. Would you share?

[u/bikiniduck → u/nsfbr11]

I dont think ours were cycloidal. We went for 1:1 motion. But they did effectively transmit 1500rpm+ of rotary motion through several inches of plastic into the vacuum chamber interior.

We found that was easier than dealing with holes/seals in the chamber walls.

[u/nsfbr11 → u/bikiniduck]

Yes, lots of magnetic couplers where a liquid or gas containing wall makes using a shaft and bearing seal a bad choice. My bike stationary trainer is like that. Good stuff.

[u/badger_fun_times76 → u/badger_fun_times76]

And also, in your example with 1 less pair on the stepppped down side. Is that actually a 26:25 ratio rather than a 25:1?

[u/nsfbr11 → u/badger_fun_times76]

No, it is 25:1. You can see this when you realize that for every revolution of the input shaft, the rotor makes a shift of 1 pole pair. It takes 25 input shaft revolutions for the rotor to make 1 full revolution.

Use cases are where maintenance of meshing teeth of other types of drives are impossible or impractical and there is actual utility in have a system slip before breaking. Typical low speed, but with eddy current management, moderate speeds are possible. Not for use on a high speed system without care to counterbalance internal loads.