ORIGINAL: gkamysz

Reducing diameter of the magnet for the flywheel causes reduced speed as the magnet passes the magneto coil. The speed of the magnet passing the coil is directly proportional to the induced voltage. If it gets too low it won't fire the plug. Stronger magnets could improve this a bit, but it really depends on what is currently used by the engine manufacturers. The magnets aren't exactly small, so a rare earth magnet would have to be quite large. A magneto system has two poles in the system, a north and a south. This could be one or two magnets. The magneto coil can't get much smaller without increasing the magnet strength considerably. The problem with making a new coil is the lamination used for the back iron in the coil. The laminations would have to be designed and made. Design is possible with some study. Producing a handful of lamination is not easy or cheap. And by handful I mean a few hundred or thousand. The thin flat plate "flywheel" would probably fail quickly due to the stresses involved when the magnet passes the magneto. This type of arrangement would not be rigid and would flex. You'd have to be careful to make sure it didn't resonate throughout the expected RPM range.

The generator idea is useful if you are going to fly for hours at a time where carrying a large pack isn't practical. For models I see no point. I have a single 2200mAh LiIon running my RCEXL in my .40 size trainer. It should give several hours of run time. I could not in this case make a generator lighter than or equal to the weight of the battery.

Link to Minimag info:

http://www.modelenginenews.org/ed.2006.01.html#5

I can see where a smaller lighter magneto system is desirable, but at the same time I don't see why a battery operated system is so undesirable.