We’ve probably all used gears in our projects at one time or another, and even if we’re not familiar with the engineering details, the principles of transmitting torque through meshed teeth are pretty easy to understand. Magnetic gears, though, are a little less intuitive, which is why we appreciated stumbling upon this magnetic gear drivetrain demonstration project.
[William Fraser]’s demo may be simple, but it’s a great introduction to magnetic gearing. The stator is a block of wood with twelve bolts to act as pole pieces, closely spaced in a circle around a shaft. Both ends of the shaft have rotors, one with eleven pairs of neodymium magnets arranged in a circle with alternating polarity, and a pinion on the other side of the stator with a single pair of magnets. When the pinion is spun, the magnetic flux across the pole pieces forces the rotor to revolve in the opposite direction at a 12:1 ratio.
Watching the video below, it would be easy to assume such an arrangement would only work for low torque applications, but [William] demonstrated that the system could take a significant load before clutching out. That could even be a feature for some applications. We’ve got an “Ask Hackaday” article on magnetic gears if you want to dive a little deeper and see what these interesting mechanisms are good for.
Thanks to [Phil Pesek] for the tip!
27 thoughts on “Simple Demo Shows The Potential Of Magnetic Gears”
I’ve often wondered about the usefulness/uselessness of magnetic couplings, but I had never thought about such a “gear reduction” setup. Fascinating!
That demo in silhouette at the end is pretty clever.
Aliasing be freaky, yo.
The coolest magnetic gears must be in the Megasonic tuning fork watch which used tiny magnetic gears for the first reduction from 720Hz
You might think of 720Hz as 43,200rpm
I think this is very similar to the manner in which a stepping servo motor works, in that there is a ratio of fixed stator coils to the permanent magnets in the rotor and that the number on the inner and outer ring differ by one … I’m probably completely mixing terminology here, but this did tweak something in my memory about how one could advance the rotor very fine discrete amounts with only something like four stator coils on the outside … can anyone else confirm this?
I agree. If you replace the input gear with two coils it would be half a stepper. If he added another bolt circle to close the flux path he could improve torque or add more steps.
There were plans available through Digital Machinist magazine for this clock fall 2011 – winter 2012:
Fascinating, nice permutation good for school activities, thanks for posting
Very cool, I went down a similar rabbit hole investigating these for a low speed stirrer. There are even magnetic equivalents of planetary and cycloid gears. Lots of potential in the right application.
It acts like a resettable fuse for over torque
Cool concept, but i wonder how efficient it is in terms of power transmission… Have you seen any numbers?
instead of bolts, ferrite cores to reduce the eddy currents would be good to increase efficiency i think.
I was wondering about exactly that. Would ferrite also be better than laminated iron pieces? Is the frequency of flux reversal something that also needs to be taken into account?
Found this one, quite interresting:
Damping of the motion of the domain walls arises from two
factors. The first factor is the presence of eddy currents. This
factor is of no practical consequence in ultra-thin metallic tapes of
1/8 mil thickness, or in commercial ferrites since their resistivity is typically of the order of 10 ohm cm. The second cause of damping is the relaxation contribution which arises from the delayed
response of the atomic spins to a force which would change their
direction; it is an inherent quality of the magnetic material.
As with all work heat is a result. Bad for magnets, if the temperature reaches the Curie temperature magnetism is reduced or is lost.
That‘s what I remembered. If the gears blocks / slips, heat‘s gonna build up even more. Shouldn‘t be a problem to cool the magnets somehow.
I’m not sure I have my head round this correctly but if you have two input discs with two magnets each on them and you could adjust the relative position, either lined up to give two pole or at 90 degrees to give 4 pole would you get a two speed gearbox?
No, the alignment of the bolts with the magnets on the driven gear is such that it “presents” only a two-pole field for pinion to align with. That is what the silhouette model at the end of the video attempts to demonstrate. To achieve a four pole coupling you would need 13 equally spaced bolts. The number of bolts has to equal the pole-pairs on gear plus pole-pairs on pinion.
I’ve also done some magnetic gearboxes. Check them out here. https://hackaday.io/project/169310-3d-printed-magnetic-wobbling-gearbox-with-cv-joint and https://www.youtube.com/watch?v=UU6y7QbaSDs
You could also incorporate a thermal torque limit by taking advantage of the Curie point, at which the magnetic properties of materials change. I don’t know it in much depth, but the rice cooker article goes into some detail.
This is a pretty cool torque limiter as well.
Once in a while HAD has something that is really cool. This is one of those times.
Perfect for weighting the output of an automatic knitting machine.
That’s pretty neat! That display is great at showing how it works too.
I wonder if this could be used to replace the torque converters used in cars?
One advantage that I have not seen mentioned before is the quiet operation. Mechanical gears normally make a good deal of noise.
Check out the Owens Magnetic it had an electromagnetic transmission
If anyone is still looking at this I made a 3d printed version at https://www.thingiverse.com/thing:4405067 that is a direct copy of William Frasier’s version, only not in wood. It works fine.
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