Building the Minimag

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NickG:
Yeah you're right John, I don't think it'd be a simple task to modify it. It'd have to be hidden away under a box I think too, don't think it'd look pretty.

Peter, the point of this is, it is self sufficient i.e. doesn't need anything else to make it run other than fuel and authentic!

HS93:
It was realy just to see if it would help madjackghengis from the post above mine. I prefer the mag as well for older engines, but some members also build more modern engines as well.

Peter

kvom:
As someone who failed his electricity classes, can someone confirm my understanding of this?

The shaft of the minimag is connected to the shaft(?) of the IC engine and acts as a generator to provide energy to the engine's spark plugs.

I haven't attempted an IC engine yet, and won't likely do so for a while, but I enjoyed following along with the build.

Bogstandard:
Kvom,

You are quite correct.

The shaft thru the Minimag should be driven at half engine speed for a 4 stroke, either thru gears or chain from the engine crank or direct from the camshaft, which runs at half engine speed. But having said that, you could run it at crankshaft speed and use the 'wasted spark' method of ignition. For a two stroke engine, you run it direct from the crankshaft.

As the magnetic rotor turns inside the soft iron laminations, it produces energy which is stored in the coil. As the mechanical points on the magneto open, the charge inside the coil is released to the positive lead (red), which, if connected to a spark plug with the outside of it earthed to the magneto, a spark will be fired across the gap in the plug.

But if you hold onto the bare wired red lead with your fingers, and turn the rotor with your other hand, you end up with a curly haircut and brown trousers, as up to 10,000 volts is produced, and your body reacts to this high voltage with the previously mentioned symptoms.

Basically, it is a stand alone unit, driven by the engine, and produces it's own power to fire the spark plug, with nothing else required at all. Turn the engine, spark plug fires, engine continues running until it runs out of fuel, or the line to the spark plug is broken.

John

madjackghengis:
John, Nick, Kvom, Peter and all, I've built Harleys for a living my whole life, as a side job most of it, with two decades in the Marines on active duty, and the single factor which most often causes breakdowns is batteries and electrical problems. I've run magnetos on every bike I've had, as well as every kind of ignition available, and having the ignition in its own, dedicated package, is as close to getting a gas engine self-sufficient as a diesel is, as is practicable. I can very easily make the points distributor or the electronic ignition distributor with hall effect parts, that are both in the engine's plans, but as John says, that leaves a battery in a box, and electronics in the box, and I want the reliability and stand alone capacity of a weedeater. While a magneto on a full sized radial engine is perhaps shoe box sized for each of two, on an engine six or seven feet in diameter, and I'll be lucky if I can get the mag under half the size of the engine its self, simply being self standing is important to me, because it more closely matches reality. In truth, I could use glow plugs and just eliminate the sparks, but then it would not be a timed, well running engine. The engine which I use for my icon, is a 103 cu in Harley engine, with both an electronic distributor, and a centrifugally advanced magneto, and it has dual plugs, one set fired by electronics, the other pair fired by the distributor. The electronics is a high tech bought piece of equipment, while the magneto set up is custom built into the engine, designed and built by myself, to match the specs of the electronics for timing and advance. I don't know at this point, if I will be successful in my endeavor to build a nine cylinder magneto, but John's build has given me high hopes for the first time since I started the radial engine three or so years ago. I have perhaps fifteen or twenty different kinds of magnetos on my shelves, dating from turn of the last century to brand new on engines, all working, and except for the very new ones, all doing it exactly the same way, with the new ones using a hall effect pickup built in to eliminate the points. John's build shows me it's possible, so I will pursue it until it fires my engine, or I give up in failure, and put a distributor on the engine. The magneto was among the greatest advances in i/c engine design, to this day, IMNHO, and it remains almost unchanged and equally effective more than a hundred years after it made its debut. I like them, they fit my ideals: "KISS, or keep it simple, stupid" and it looks possible. What more could a model engineer ask for? :nrocks: :headbang: :beer: cheers, mad jack

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