I'm thinking about making a helicopter pigeon where, to turn, I would need a seperate motor to spin a propeller and move the front/rear which would be activated by pressing a key. How could I do this?
I don't think this is possible, at least not easily. A better solution I think would be making it controllable with some LUA function rather than a motor, however I have no idea how that could work. Maybe take a look at how it's done in the Super Gnat mod.
Possible but could have side effects so I don't advise it, unless you are able to set the force of them just right, enough to make it rotate at the speed you need but not more
Take a look how it's done with JATO, it doesn't need a full on controller btw, just a LUA file that defines the variables you will use for it, but making it a controller is good because this way you won't have errors if you click the button when the part isn't equipped.
I guess similar to what you would have when using hydros, could be very simple, only a small portion of the JATO LUA is actually for the thrusters and controls, you could figure out which parts are for sound, glowmaps, fuel, etc. and not use them (though it would be cool to have fuel that can run out in the motor). If you can't figure it out I could try to do it for you later.