Using Multiple Magnets to make a single pole.

[modern_messiah]

Hi all,

Just a really quick and lame question - I don't currently have the items (nor past experience) to be able to figure this one out on my own so I thought I'd ask here.

Is it possible to create a single pole using multiple magnets? So say you need a 12 pole rotor, but certain design constraints and a lack of appropriate tools led you to attempt to make the 12 poles from 24 magnets, could you place 2 magnets directly beside each other (touching) with both of their north magnetic poles facing outwards and repeat but with the next set facing in. Obviously there would be a gap between each magnetic 'pair' - the poles of your motor.

Is that explained clearly enough? At first thought I figure it can be done but then I can't decide if the 2 magnets would screw with each other and defeat the purpose.

Stupid I know - but I hope simple and easy enough to explain that someone can help me out.

Thanks.

- Matt.

 

[amberwolf]

I don't know if it will work or not, but it is going to be pretty hard to put them together--have you ever broken a (powerful) magnet, then tried to push it back together? It's really hard, because even though all the parts' poles are the same as the original orientation, they repel each other and attempt instead to stack some other way.

 

[Kingfish]

The answer is Yes.

There are numerous studies by enthusiasts and students that have used that very same concept to build out their designs. Early on I too have considered using cube-shaped magnets to create the desired configuration. See my sig: AF motor studies midway down on Page 2.

~KF

 

[modern_messiah]

Thanks Kingfish - I was hoping you'd reply. I have been following your theory thread but it so big now it's hard to remember some of the contents :?

Amberwolf does raise an interesting problem however, and something I wonder if you (Kingfish) have actually attempted in practice and not just theory - placing the magnets side by side. I might just cough up a few $ for some small rare earths and try it for myself.

It'd be the smart thing to do lol.

 

[Kingfish]

Thanks Kingfish - I was hoping you'd reply. I have been following your theory thread but it so big now it's hard to remember some of the contents :?

Amberwolf does raise an interesting problem however, and something I wonder if you (Kingfish) have actually attempted in practice and not just theory - placing the magnets side by side. I might just cough up a few $ for some small rare earths and try it for myself.

It'd be the smart thing to do lol.

If you arrange them N-S in a row then you’ll have a longer magnet. I dropped the idea in lieu of better design; didn’t want to mess around with 2-, 3-, 4X more parts. Try to consider ease of assembly; make it simple if you can.

And to be clear, two magnets side-by-side with the same poles at each end will repel with all their might. I’d avoid that type of configuration.

Cheers, KF

 

[modern_messiah]

Here's a diagram. Hopefully it helps. The motor is a traditional in-runner - the whole point of this is to reduce the air gap between the rotor and the stator. Larger magnets are all well and good (and more powerful) but the air gap is HUGE and 3 smaller magnets of say a pull force of 2 kilo's is almost as strong as a single larger magnet with a pull force of 6kg....in my head anyway. I'm not try to create something fantastic or even approaching the level of thought that you are with the AF motor - just something easy, gung-ho and workable. If this spins when I'm done i'll consider it a success.



Please note this is looking along the axis of the motor rotor. Each gray block represents 1 magnet of dimensions 4x2x30mm with the magnetized direction through the height of the magnet (2mm). In this example (and I've done a lot of fiddling) each pole of the rotor is made of 5 magnets. The red dooted line represents the inner surface of the stator coils. The rest of the circles are just air holes and other random cr*p.

Here's a link to the magnets used in the above example: http://www.frenergy.com.au/products/Block-4x2x30-mm-N48.html

 

[Kingfish]

That configuration looks promising; I think you have it sorted 8)

I'd give it a shot and see what happens.

Neat! KF

 

[modern_messiah]

Unfortunately I am currently in possession of 65 next to useless magnets

My 'plan' (I use the term plan very loosely lol) to use 5 to make a single pole has not worked as the magnets are impossible to place touching each other with the same poles pointing outwards from the rotor. I actually managed to snap one magnet in half(!) trying to get them side by side. I thought this might be the case but took a punt anyway. The term "Fail" seems appropriate.

Could I possibly use 3 instead of 5 to make the poles? Basically remove the magnet either side of the centre magnet for each pole. They do repel each other but it’s much easier to hold them in place. The magnets in each pole would all have the same magnetic pole pointing outwards. There would now be a gap between them, but the group of magnets would be attracted/repelled by the same tooth at any given moment. I'm just worried that the air gap between the magnets will cause issues and I'm not technically inclined enough (yet) to determine how detrimental this would be to the performance of the motor.

A quick test shows that 3 close to each other magnets, all with their outward facing pole pointing in the same direction, act like a single larger magnet. However the magnet that I use to test the attraction/repelling forces can be pulled into the gaps between the magnets. Despite this I am using the same type of magnet to test the ‘super-pole’ as the ‘super-pole’ itself is made from. With a larger magnet the attraction into the gap is smaller because the repelling/attraction forces are larger. The larger magnet better represents the teeth of the stator. See my very basic and rough musing below:





Any ideas? Is it worth attempting or should I just go for larger magnets and increase my air gap between the magnets and the stator?

 

[modern_messiah]

I tested this last night using the setup exactly as described above. The smaller 2x3x30mm magnets arrange as 3 side-by-side to create one pole. The magnet I used to test the setup was a single 45(L)x20(W)x10(H)mm magnet. This is ROUGHLY the size of the coils in the stator. The larger magnet definitely felt as if it was being repelled/attracted (depending how I was holding it) but the entire pole. It wasn't trying to be pulled into the gaps between the 3 magnets or anything.

I feel doing this is better than single larger magnets for the poles as the air gap between the face of the magnets and the stator is over 5mm which may in turn negate the benefits of the single larger magnets over the 3 smaller magnets.

Seems like a go-er to me. Winging it big time!

 

[EDS]

If you're going to use multiple magnets together, check out the Halbach array. If you arrange adjacent magnets with the poles alternating in a particular pattern it effectively makes 2x the flux on one side, and no flux on the other. You'd want to use magnets with a square cross section though since half of them will be sideways. It would still be a pain to hold them in until the glue dries but it should be much higher performance than any normal arrangement.

I heard somewhere that a motor company has a patent on using this. I'm curious if anyone knows who that is or anything about the motors with this magnet arrangement. It would be too much trouble (expensive) for most applications, so it's probably some big industrial model. I'm sure some enthusiasts would go for it also. One of the kit motor sites could have the option - if the patent isn't too restrictive.

Good luck.

 

[modern_messiah]

I don't think I could create a Halbach array with the magnets I have but I had not even considered the option (though I know a little about Halbach arrays).

I will look into it tonight a bit more. Maybe I can create a pseudo halbach array :?