I posted these in the Helicopter forum first, but brought them here for everyone to see.
This is a couple ideas I sketched on how to build a working, synchronized tandem rotor installation, using simple applications. They are rough, but I hope useful to some. [:)]
That’s a great idea. Hope you can do it! The flex-shaft is probably the best solution. You don’t have to worry about gear alignment. Is it going to be motorised or you just want to turn them by hand?