Hello,
I have a question regarding the Ardupilot Autotuning.
Is there any documentation about the tuning method from a flight control perspective?
Thanks in advance!
How to methodically tune (almost) any multicopter using ArduCopter 4.4.x contains explanations on how to use it and what it does. It also contains links to the System ID Mode Operation — Copter documentation where you can see detailed control diagrams. If you have any other questions just ask.
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I have a question: To what size can a quadcopter be adjusted using auto-tune?
Any size, From 80 g to 400 Kg.
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I would divide the lower limit by two, from my own experience 
Most people’s trouble with Auto Tune is they believe they can take a completely untuned vehicle perhaps with the initial tune parameters set, take off, hit a button and the magic happens. That is rare and the reason there are error messages given during Auto Tune telling you why it won’t run. On small craft the PID’s are often way too high and the outputs are oscillating wildly. On large craft the PID’s are too low and it lacks authority to perform the aggressive moves Auto Tune demands. The fact is some work is usually required before running it.
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Yes, I agree, people don’t want to understand the intricacies of the little things. And this is the key to success. To be honest, I made a lot of quadcopters, but I had a break for a year and I thought that some algorithm had changed. Because before, a quadcopter was enough to simply assemble well. I have I mean, the balance of traction and weight, the rigidity of the frame and good equipment, then you could turn on auto-tune and it would adjust everything
I think the question was asked for an airplane autotune. I control the plane on a radio control channel without a flight controller and it flies the way I want. For this case, the plane doesn’t need the PID parameters from my head because the plane is designed for stable flight and if I don’t control it, it has to fly itself. I choose planes that have this property of flying on their own, so with the PID parameter setting, one flight is enough.Documentation can be found here Automatic Tuning with AUTOTUNE — Plane documentation (ardupilot.org)
Good video for auto-tuning https://www.youtube.com/watch?v=vzFQEb9WnfU
This is my video of setting up a PID in one flight https://www.youtube.com/watch?v=bIjCWCS65aM
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Yes, sorry for the digression. I was responding to Ilya’s post and didn’t realize he had missed the context of the thread too.