Hello guys, I am building a X8 Octo with apm 2.6( AUW 6.5kg, with 18" props) I am afraid to fly for the first time with the stock pids, do you have any suggestion where and how to start?
I installed the 3.1.5 firmware on the APM.
Please give me a hint.
My humble experience. 
Place your X8 on a flat surface and take off slowly.
You’ll see soon how tit reacts. even if you’re on foot in the air.
If it wobbles a lot (which I doubt) land it.
You can lower the pitch and roll P-PIDs.
For example by 20-30%. Your X8 will become “sloppy” ,but you’ll see that when you’re only 1 foot in the air.
If you thrust it, put it up to 3 meters, put it in alt hold and do an autotune.
Than tune it further.
Good luck and happy flying.
Paul