I've made a little video explaining my problems, it looked like the most direct way of explaining them to me.
In short, apart from the fact that i had my pusher and normal prop inverted (and thus i wasn't able to lift), with the throttle lowered at the minimum spinning speed, some of the props are stopped. Trying to tilt the copter doesn't create a behaviour that makes sense to me. The accelerometer of the APM is perfectly calibrated (and i can see it from the flight data panel).
(i've tried to run the motor test utility via CLI, but it doesn't seem to do nothing and the command returns a blank after about one minute)
Any suggestion is welcome. Thanks.
Friend of mine had a similar problem and it was corrected by turning the receiver...making it face the front of the aircraft. Don't know if this will help???
DJI OPTO ESC's cannot be calibrated, if it will not lift off I believe there is some basic configuration errors have snuck into the build.
Cedivad, when the props are rotating, is there air coming off your props that is blowing your hair back? If your wearing thongs (Google it) your should feel a breeze cooling your toes all the way around the copter.
The picture below explains which way your props should be turning, and by the way, your hex does not use pusher type props at all, there all tractor or pull types, the sequence starting at position one is self explanatory.
To get an understanding of identifying the difference between clockwise (CW) and counter clockwise (CCW) rotating propellers go here: CW CCW Props
Oh, and one more thing, you may want to post this problem here: Ardupilot Forum
Hopefully you'll get your Hex to defy gravity.
I just wanted to thanks everyone for their answers, i'm still unable to lift in stabilised mode (it seems unstable and i don't trust it), but loiter mode works perfectly. I can takeoff without any problem. I already had my first crash (most probably due to the battery since that they are now dead at 6V, i have now enabled the battery failover).
What else can i say? Just thanks.
You did mention that loiter works, however i will recommend that you verify your motors + props are correctly setup. While on the ground and armed, try a little roll right, the left of the copter should lift just a bit. Repeat in reverse for roll left and verify the copter lifts to the left. Try with pitch up, the back should lift just a bit and reverse with pitch down. Just push the direction just enough so the side lifts 10 cm or so you dont want to flip the copter. This helps verify the motors and props are correct. Once your happy all the axis are working you can try vertical and take off if your confident now.