After struggling with taking of for about 2 weeks, I think that I finally found out that my APM card makes BAD outputs for the motors.
In fact, when I look at the logs I can see that :
With auto-analysis I have a WARNING message (highlighted in blue in the first screenshot, link below) : Test: Motor Balance = WARN - Motor channel averages = [1248, 1268, 1149, 1209] Average motor output = 1218
Difference between min and max motor averages = 119
By analysing manually, I can see that in fact, the outputs are bad (on the second screenshot, you can see the legend with the arrows I drawed in green : arrow 1 shows the legend , arrows 2&3 the big differences between the motor outputs in response to the " RCin " and arrow 5 shows what I looked at.
I could confirm that something was wrong when I looked at the the "failsafe" section in MP (under "mandatory hardware" ), the radio 1-2-3-4 outputs in the right culumn (called "2nd flight mode") reacts a bit weirdly ( 3rd and 4th screenshots show what I have when I put throttle at maximum) even without props, and even without the connection to the ESCs, so I don't think it's because of them...
I'm quite frustrated because I can't take off, the quad reacts as if it was drunk, and eventually always crashes as soon as I stop to compensate with the joysticks)... even if everything seems really fine ... (I have been through the troubleshooting guide of ardupilot many times, recalibrated and rebuilt the quad 3 times, checked everything was alright). Rmq: I have a 2-3% difference in the minimum throttle between 1 and the other 3 motors, but I calibrated the ESCs 10 times and can't make it any better...and I read that this should be an acceptable difference.
--> So does andbody have an idea about HOW to correct the motor outputs of the APM ?
Thanks a lot for your time