Piston-wheel mechanism

I’m trying to animate a simple piston-wheel mechanism, like the ones in the locomotives, but after trying different constraints it still doesn’t work. Can you help me?
Thank you in advance!
Finally, a simple solution:
After studying the tutorial sent by SoylentGreen, I’ve obtained a simple solution (just one armature with two bones and three empties) that you can find in: http://www.pairal.net/3d/Flywheel.blend

Yeah, this is not so easy.

Thank you, I’m going to study this (it seems much more complex than I thought).

After studying the tutorial in http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Advanced_Tutorials/Advanced_Animation/example/_Piston%2C_Rod_and_Crank I’ve found a simpler way to obtain the same, with only one armature.
You can ge the blend in http://www.pairal.net/3d/Flywheel.blend

I’ve simplified a little more the mechanism. Now there are only one armature (with two bones) and three empties.