Servers by jDrones

Proper plane trimming procedure?

(Gabriel DeVault) #1

Can someone please explain the correct procedure to establish trims for a new aircraft from scratch?

Do I enable servo_auto_trim?

I’m going to assume I 1st fly my maiden flight in “manual” mode and set the RC trims where I want them. I am unclear on the next step. I assume I switch to FBWA or FBWB, but how do I apply trim in this mode without affecting my manual trims?

A very clear, step-by-step tutorial, would be extremely helpful.


(Gary Mortimer) #2

What I do is find the trims in manual as you suggest, then land and then change them physically on the control surfaces and set the RC Transmitter to zero again. Then I run an autotune, that normally is enough.

(Gabriel DeVault) #3

Thanks Gary, that seems like it would get us “close” but never “perfect”. And it seem inelegant, and there should be a way to just do it in software?

In one of the wiki docs I read to trim the plane in manual, then land and re-cal the RC channels in AP. This way the manual RC trims are unchanged and AP sees this as neutral.

Can’t find that link any more, and still seems like this is a very fundamental “low-level” setup thing that should be well understood and documented…

(Gary Mortimer) #4

You can add auto trim in after that autotune and it will be as perfect as it ever can be. You could chase your tail forever seeking a perfect tune, At the end of the day a well set up properly balanced and true airframe always beats something where the autopilot does all the work.

(Gabriel DeVault) #5

Totally agreed. Additionally, squishy foam airframes will never hold “true” anyways, so a quick and easy software trim process would be highly desirable.

How does one “add auto trim”?


(Greg Covey) #6

Hi Gabriel,

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.
  • Autotune
  • Skip TRIM_AUTO and simply enable SERVO_AUTO_TRIM
  • Probably others…

Here are some tips that Tridge gave me:

[quote=“tridge, post:8, topic:21444”]
The RCn_TRIM should be set according to your transmitter (via Radio Calibration), and has nothing to do with the servo outputs.[/quote]
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.