Hugh Piggot 6' Question

[bluehunter40]

Hello all,

So I received my book yesterday, and started reading. Once I noticed that the 6' HAWT uses only a steel disk and not a full rotor I skipped around and don't see much explanation for that (not that he needs to explain to me). I was just thinking about it, does this better focus the flux? I will keep reading maybe I will find the answer I am looking for, but it would be nice to know my logical thinking about this is "on track".

Thanks

Tim

[bluehunter40]

Okay, it uses one rotor with magnets and one steel disk, I can't type as fast as I think... So the second steel rotor w/o magnets does what?

[ghurd]

It completes the magnetic flux path,

meaning it gives the flux a place it wants to go.

It focuses the flux, instead of having it go off the magnets willy-nilly.

Might google search the board for "FEMM".

There are renditions showing how the flux acts under different circumstances.

Tighter flux is better.

G-

[Flux]

I thought you would come back with more questions.

Ideally we should use the magnets to best advantage but sometimes other factors come into play.

With a range of machine sizes Hugh has standardised on a magnet that is cost effective and readily available. For the little machines it makes a lot of sense to use the same magnets. Realistically it is difficult to use less than 8 magnets without running into trouble with the space for the hub. It is therefore not a bad idea to use those cheap magnets in less than the most ideal way.

The 4ft machine is just a single rotor with no return path for the flux and it suits the 4ft blades and is nice and easy to build.

The larger machines use dual rotors with magnets on both discs. This makes best use of the magnet. The 6ft machine could have been built dual rotor with magnets on both but it is possible to get enough flux with magnets only on one disc so this version is cheaper.  It does use the magnets far more effectively than the single rotor and is really the equivalent of having magnets on both discs but half thickness ( non standard magnets). There is a bit more flux leakage with this method and it needs a thinner stator for best results but as it suits the 6ft prop well then it is a cheaper machine to build than using magnets on both sides and having to increase the gap to drop the flux to a level that suits the blades.

I hope Hugh agrees with this, this is my take on why these things are done this way.

I have used this method with the magnets on one disc and return disc for the flux and in some cases it actually makes better use of the magnets to do it this way than use a similar number on smaller discs. Apart from effective magnet use, the hub takes up a lot of space in the centre of the stator and if you try to use small discs you just run out of space.  I think this is why the magnets are turned round in the 4ft machine as the original version had a strange mechanical layout to solve the hub problem.

There is always more than one way to get the same end result but many factors come into making a good design. Doing a design for one machine may have led to another solution but with a range of designs it helps to use many common parts.

Flux