Multiwii Drones

Any DIY drone builders out there with experience using Multiwii? I teach high school and have some students who are trying to build their own drone, but we are having problems that we can't find solutions to on the Internet. Would anyone be willing/able to help us out? There is a MultiWii forum, but no way to register.
Right now, our biggest issue is with an imbalance in motor speed. Two motors have a quicker response time than the other side and so the drone just flips on take off.
I can give more details if anyone thinks they are able to help, but I don't want to spend too much time posting if their isn't anyone out there...

Thanks!