Since some of us are getting more in depth into the PID issues with the quads, I figured I would post a link to this little demo. It's old, clunky, and written in visual basic 6 but it is a good learning tool to play with a PID simulator. http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=32561&lngWId=1
I attached a compiled version for those who want to play with it but don't have vb6.