# Would this be the best permanent magnet design for vertical rod?

I'm trying to design and build a small vertical wind turbine that is held in place by permanent magnets, i.e. the rod with the blades on is held using magnets and gravity and allows the rod (that the blades are attached to) to spin with as little friction and as little magnetic resistance as possible.

I'm going to build this with a 3d printer, and I'm just starting out and wondered if there was a design that someone knows of or could think of that would allow such a rod to be held in place (given that wind will be pushing against it) but allow it to spin at the same time.

My initial idea is to have a disc magnet on the rod (rod is shown as the vertical black line) - where the rod goes through the middle of this disc magnet (shown in red in the diagram below) and have its outer circumference poled differently from it's inner circumference. Then have a disc magnet above and below this disc (shown in blue) where the same pole is facing the disc around the rod, but the inner diameter of these two discs are larger than the diameter of the rod and is not touching the rod. Each of these will oppose the disc attached to the rod thereby holding it in place but allowing it to still spin.

See below for a very basic diagram of my initial design:

The black bar in the middle is the rod. And for clarity, the south pole on the red disc is at the innermost part of the disc magnet and the outer edge is all north polarity.

Couple of quick questions:

1. Do you think this would work?
2. Do you think there would be any magnetic resistance on the spinning of the rod due to this design? Or more importantly, would the resistance be more than say the friction resistance of using ball bearings?
3. Do you think it would have to have nanometre accuracy in order to remain stable? Do you think with the slightest breeze pushing against it, it might jump to some point of highest polar attraction?

If anyone can think of a better design, I'm open to suggestions or modifications to this to make it more stable or reduce resistance.

Edit: The size of the wind turbine blades will likely be no longer than 250mm in length and a width of only 70-80mm each blade so this is NOT a large turbine. The aim is to achieve (if possible) about 10 watts at 5mph wind speed.

• this design is not feasible until you add structures to keep your magnets from being repelled off, flipping, and smashing into your rod. (in this case the blue N attracted to the red S would smash blue into black.) once you start adding structures to prevent that, you will likely lose benefits associated with floating the rotors very quickly. get yourself some magnets and try to float something...
– Abel
Jan 31, 2022 at 12:15
• It seems to me that this is a good example of a metastable system. It remains stable in the floating state only if all elements are ideal and exactly, perfectly identical. The slightest perturbation moves the system to a different stable state where the rod is no longer suspended or free to rotate. Jan 31, 2022 at 13:08
• Just make your life easier and use a ball bearing. Jan 31, 2022 at 16:35

## 2 Answers

What you ask for is prihibited by the Earnshaw's theorem

You must use other methods to provide stability. Few extreme cases exist where magnets can hold an item, such as diamagnetism, superconductivity, levitron toy. Also few examples of magnetic bearing, where either stability is achieved through rapid rotation like in levitron, or through active sensing and acting.

None will work for a magnetic bearing for a cheap device that can also stop, and stay unpowered for days.

1. Your design wont work. It is not stable.

2. There is some resistance due to magnetic field unevennes, but it is orders of magnitude less than in a ball bearing.

3. It will not be stable even if done with nanometer precision. Even smallest thermal movement of particles will make it unstable over time. Time of stability can be increased from fraction of a second to a few seconds or minutes with the best tech and cooling available.

As mentioned previously, this design, while it does illustrate repelling force fields, is not complete enough to be stable. Stability may be achieved if another such set of magnets was placed either above or below.

If the outside magnets shown represent halves of ring magnets, then thier magnetic fields will repel all sides of the center pole magnet; that will function ok. But if those are separate magnets, then a third set of magnets must be used equidistant from the other two, otherwise the center magnet will slip out from between the two illustrated.