this post was submitted on 26 Jul 2024
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The weight of the blades on a typical windmill is aligned with the plane of rotation, so most of the forces are taken up by radial bearings:
They do need thrust bearings as well, but only to resist the force of the wind that isn't converted into rotation.
Vertical windmills, however, rotate perpendicular to their load and require a thrust bearing to support the full weight of the blades at all times:
This means that vertical windmills wear down the single thrust bearing that supports their weight significantly more quickly than others who can distribute the weight of the blades across multiple radial bearings. It's not a huge problem at a small scale where the weight is minimal, but as the weight per bearing increases, the rate of wear does as well.
I was going to respond, but you did way better than I would have!
Non-engineer here, thank you for a strong ELI-average-adult.
Fantastic explanation and diagram inclusion
True that, and very well explained I might add.
Now, if I were on their engineering team, I'd probably try a combination of magnetic and roller bearings. Use magnetic bearings to support the weight, while securing everything in place with radial bearings.
That way, the mechanical bearings don't have to support the weight, magnets can take care of most if not all of that, saving undue wear and tear on the mechanical bearings.
I dunno, just a thought.
Actually, magnetic bearings experience wear as well.
So called "permanent" magnets gradually lose their charge over time through interactions with opposing magnetic fields, heat, and mechanical stresses. Neodymium, for example, loses about 0.1% of it's field strength per year even when it isn't being used for anything. This is why you can't use magnets to make perpetual motion machines:
Magnets are basically batteries that store energy in the form of a magnetic field, eventually they run out of charge and need to be re-magnetized.
This makes passive magnetic bearings really tricky to design, so most of those in use are active types that also employ sensors and electromagnets to ensure stability. These electronics also degrade over time, so usually a mechanical bearing is a better choice unless the use-case requires a frictionless axle.
Everything degrades over time, that's a given, nothing lasts forever. But if they relieve the weight from the mechanical bearings with magnets, then they might last quite a bit longer before needing service.