Another version of how not to build a model engine

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NickG:
Mad Jack,

Wow, that's impressive, didn't know he was that well known!

The bob shores one sounds interesting too BC.

Nick

sorveltaja:
That magneto thing is interesting... how small can be made?

I have ETW's 'Atomag Minor' plans for miniature magneto and the coil. Drawing has the magnets diameter ~30mm(~1.18"), and its material is alnico.

With modern neodymium magnets, maybe even smaller size (and more efficient?)would be possible?

Bluechip:
Folks

The principal problem with mags. miniature or not, is the HV coil.

This consists of some 15,000 turns of very fine magnet wire. about 44 AWG, or it's metric/SWG equivalent.

The breaking strain on this stuff is near zero. If it lets go, you start again. I have wound coils on a commercial winder with wire a good bit larger. I broke that! You won't do it on a lathe unless you are very lucky indeed.

(BTW, those coils were not for ignition stuff, just rewinding solenoids).

Assuming you have succeeded in making the coil, you then have to vacuum impregnate it. This needs to be done to give a path through the coil to get rid of the heat. Otherwise, you get a hot spot, and the coil will fail.

Then, there is the problem of sourcing the armature stampings ...

There was. at one time, a UK maker of Mini-Mags .. no longer in business I think. (Jim Shelley).

Some reference here.. by some one we once knew, I think.

http://www.floridaame.org/discus/messages/14/321.html?1182878736

There is a wealth of practical information in Bob Shores book. I strongly suggest anyone even contemplating home building coils/ magnetos gets a copy and reads it before committing any significant time or money.

Dave BC

sorveltaja:
Dave, it sure is tricky to wind hair-thin wire. I've been trying that, and there is way too big chance to snap it.

Unless you have a delicate winding setup.

sorveltaja:
In the meantime, I've done some more testings with vapor carb.

Earlier I just couldn't get it to work with ethanol. But today I almost accidentally found out, that it's all about temperature.

With gasoline it hasn't been a problem, since it has lower flash point, than ethanol(just a guess).

I remember reading somewhere, that it could be tricky to start the engine, that uses ethanol with vapor carb on the cold circumstances.

I was in doubt, when I tested following:

But it seems, that even few degrees increase of temperature makes ethanol to vaporize :ddb:. Once the hand is removed, lukewarm is gone, and soon the engine stops.

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