If you start with TRIM_AUTO enabled and trim the plane initially in Manual mode, those trims will get transferred to the flight controller when you change to any other mode. This can be a good start if you are unsure that your plane is even close to trim.
If you then disable TRIM_AUTO and enable SERVO_AUTO_TRIM, this enables automatic servo trim in flight. It works great!
In between these steps above, there are many "options" to choose from.
- Use Gary's technique of physically changing the linkage and reset trims.
- Skip TRIM_AUTO and simply enable SERVO_AUTO_TRIM
- Probably others...
Here are some tips that Tridge gave me:
Paraphrase: The SERVOn_TRIM controls trim of the servo outputs.
On my last several projects, one plane and one quadplane, I simply enabled SERVO_AUTO_TRIM and the first (forward) flight was done in FBWA mode. It was amazing to watch how quickly I could let go of any stick offset and it would fly straight.
For example, on my mini Talon QuadPlane, it was built as a QuadPlane so I never flew it before hovering it. The first transition from hover to FBWA worked great! I used the same path on my FireFLY6 conversion from AvA to APM. Other plane projects, I have used Manual mode and TRIM_AUTO and then Gary's linkage correction technique. These were on releases before v3.8.