A completely new version of the copter recently did it's first flight. I rebuilt chassis, electronics and replaced the battery. I was able to save 35% weight (996g -> 628g). Outdoor flight tests still have to be done. But I am really looking forward to that. Lowering the kinetic energy might significantly increase flight performance.
P.S.: In the meantime I did three outdoor flights: Absolutely great!! I can hardly believe that I built this thing on my own ;-D. Lots of power, very agile and absolutely precise and fun to fly!
Currently, I am working my way through the source code (cleaning up and adding comments), so I can post it here. The electronics circuit + PCB will also be made available.