Finally my x550 and APM2 quadcopter is complete! And I have successfully flown!.
Right now I seem to have a bit of yaw problem, as well as a trim/balance issue. Since the frame is not quite flat it can be hard to tell exactly what should be level, and when I yaw in a different direction, it seems to always return to original. I think I need to check my motor position perpendicularity and possibly PIDs.