Tim's Magnet-Piston Engine Design

[tim123]

Hi Gyula, yes that's exactly the shape I had in mind.

I agree - the magnetic fins would be magnetised thru their thickness, but that will result in the rotor & stator being strongly attracted. Just like a stack of magnets will line up.

This is also like a Reluctance motor - the rotor & stator will come together to minimise the flux-path length. So either way I think it should work.

[gyulasun]

Hi Tim,

You may be right, I possibly mixed up this rotor shape with Butch LaFonte's perpendicular magnetics and his tests with washers placed between two facing (NS) magnets. Obviously, in your latest setup the NS field orientation is shaft-wise while in Butch setup with the washers it is radial-wise hence the washers repel each other.

Butch's tests are in this link: http://98.130.116.247/shared/manager.asp?d=files\ButchLaFonte\Perpendicular%20Magnetics\Video_clips\  and I mean this video:  BalanceTip1.mov (best if you download).

I have a question on your stator shape and drew a rough sketch. Will the stator have the wall thickness at all or it is just not erased in your original drawing fin-motor.gif (like the circle around the rotor)? I believe this is important because as I sketched it reminds me a kind of Faraday cage i.e. blocks magnetic fields to penetrate the inside volume...  What do you think? (This is why I mentioned the stator screening the rotor the other day.) Somewhere the stator ought to be cut into two parts, just due to assembling issues with the rotor and the cut may or may not solve field blocking? Or you think this is not an issue at all, regardless of the stator 'cage' shape (the continuous wall thikness)?

rgds, Gyula

[tim123]

Hi Gyula, I have wondered about the wall thickness for the stator. I think the wall is a problem - not because it will block the field - but because any rotor/stator faces running axially will repel - so an outer wall will reduce efficiency. Ideally only the radial faces would exist. However, that does make it more difficult to build. Thinner fins = less axial faces vs radial...

The rotor & stator have to be strong - it's an engineering challenge. I'll give it some thought...

- The stator fins could be made of steel sheet, cut to the shape shown previously, with tufnol tube spacers between - to provide the spacing for the rotor fins. They would all have to be bolted together - down the length of the coil - and into the casing (non-magnetic bolts). Would lose considerable diameter this way though.

- Could use brass spacers, and machine them to key into the stator plates. Would lose less diameter that way...

- Stator could be made of brass tube, with steel fins braised in place.

- Could make each stator segment a separate coil. So the stator fins would be the bobbin ends. Easy to bolt together from the outside then...

So there are a few options I can think of immediately... I'll have to have think about it some more with a glass o vino...

[Low-Q]

Dont worry about the area. You can focus on the circumference where the torque is strongest. That way the fins do not need to be so big, but narrower and stiffer. This will wash away the problems with magnetic stress that is pulling and pushing on the fins. Only 10 - 15% of the radius is neccessary to have fins. The magnetic flux will find its path through a more narrow path where flux density will be much greater plus that you have focused the torque as far from the shaft as possible. More power and better rigidity. Less inductance also means more power at higher rpm.

Vidar

[tim123]

Hi Vidar, thanks for your input. 10-15% of radius sounds reasonable. I am concerned about stresses on the fins (and axially along the shaft too)...

I guess - if less inductance is better - then only the fins should be made of magnetic material - and the shaft & supporting structures should be non-magnetic... I suppose less iron in the core = less inductance means less input power required, and lower transient time, hence higher frequency...

Thinking about it, I guess there's no benefit in in magnetising / demagnetising bits of the rotor which aren't facing the stator - it'll just result in lost power, eddy currents, heating etc.

:-)
Tim

PS: I've started a new thread for this design - as we're not actually discussing the piston design any more...
http://www.overunity.com/13692/core-rearrangement-fin-motor-open-tech-ou/