For anyone having balance issues, a few tips i've learned from this past weekend:
1. Having both rotors on the same precise vertical axis helps. A lot. By this i mean you should build your copter so that the fixed rotor and free rotor are essentially 1 above the other (not distance wise, i am NOT referring to the ditance between the two rotors, just in terms of relative position).
2. Make sure your rotors are balanced. Now, assuming your building a ribbed mylar rotor (or other type of material, i think japanese tissue paper is also popular?), the wooden frame should be made of wood that is hand picked for the right mass. Use strong stiff sticks for the main long pieces, and use lighter stuff for the ribs. Make sure the mass on both sides is about the same by massing the cut pieces before hand. This helped me a lot going from my 2nd heli which was terribly unbalanced to my 3rd heli, which wobbled nowhere near as much. Continuing on, when putting on the mylar, assuming you make no mess ups and don't have to patch (and a little bit on that later), the finished product should be fairly well balanced.
3. About that patching up business. Don't even go there. Unless it's a very minute error and can be fixed with just a little bit of covering and glue, just start over. Patching up a tear that's more than a few millimeters in size is going to 1. add more weight on one side, making the rotors unbalanced, and 2. if you happen to care about aesthetic value, it just makes for an ugly copter. Either way, with a good jig, it should take less than 45 minutes to make a complete rotor, and hey i do it by myself so i would know,
Hope that helps, balance is a key to making your copter as efficient as possible.
2011 Season Events~
Fossils (Regionals ~1st) (State ~6th)
Towers (Regionals ~1st) (State ~3rd)
Helicopter (Regionals -3rd gahhh) (State ~5th)
Wind Power (Regionals ~1st) (State ~3rd TIERED!)
Hooray for getting everything i wanted?