What does it do? I just updated the APM Planner to 1.1.77 and it changed the TRIM_THROTTLE from 425 to 531. I just started to re-tune my PID and throttle hold went first. Bam! The heli hit right to the ground in a split second as soon as I switch the mode. Bench time again!
I think that all sounds right, if I understand what you're doing.
If Ch1 is purely the "throttle" output, the effect you're doing is due to "throttle boost". Basically, the entire throttle is increased when you lean the aircraft over to attempt to account for the fact that as the aircraft leans, a component of the thrust is to the side, and it's not all going down. So, we automatically increase thrust to try and maintain altitude.
Ch4, probably not surprising. The output should be stronger on rate than on rotational position. It's just the way the maths work out.
If you rotate the board fast, the response should be strong. That is the Rate P acting. If you rotate the board very slow, the response should be lower, but you should see it increase as you rotate the board further. That is Stab P acting. If you increase Stab P, then then you should see the value increase faster with the rotation position error.
Thanks now it's clear.
In this experiment I want to have purely the "throttle" output on Ch1 without "throttle boost". Do you know in which library (or .pde) can I find the code responsable for this mixing?
Finally I want to make other kind of mixing without "throttle boost".
What you're looking for is the variable angle_boost, and the function get_angle_boost which is in Attitude.pde.
Thanks now you put me in the right direction.