Auto Trim¶
Auto Trim (ported conceptually from Rotorflight/iNav's BOXAUTOTRIM) captures trim automatically from sustained stick input: hold a small, steady correction in cruise flight, and Auto Trim gradually folds that correction into the aircraft's trim so you no longer need to hold it.
This is particularly useful for dialing in trim on a new airframe without repeated land-adjust-relaunch cycles.
How the capture works¶
Flip the switch on while armed and hold a steady correction for about 2 seconds -- Auto Trim averages the actual, already-mixed servo output over that window, and the difference from the servo's center becomes its saved trim: the value in the Servos tab's Trim column. Mid and the Min/Max end stops don't change, and the trim is limited to 20% of the servo's Scale like any other trim. Only servos actually fed by a stabilized axis (roll/pitch/yaw) are touched -- outputs driven purely by a raw RC channel, an override, or a logic condition are left alone, since those aren't part of the drift this feature corrects for.
Flip the switch back off before disarming and the capture is abandoned, restoring the previous trims exactly -- nothing is written unless you disarm while the new trim is still active, at which point it's saved the same way any other live-adjusted value is (on disarm).
If a Mapped Servo Trim knob is also in use, its offset is left out of the trim Auto Trim saves. The captured trim is what the aircraft needs without the knob, so the knob keeps working on top of it instead of being baked in and then applied a second time.
A bus servo cloning a PWM output isn't trimmed itself: it already carries its PWM servo's trim.
For a manual alternative -- nudging an axis's trim by a fixed amount per switch press, rather than capturing a sustained stick correction -- see Trimming in flight on the Servos tab. To make a trim part of the center, use Move trims into Center on the Servos tab.
Trying it on the bench
Auto Trim only starts while the aircraft is armed, and arming is blocked while the Configurator or the CLI is connected over USB, so it can't be tried that way. To check it on the ground, power the model from its battery with the props off and no USB, arm, tilt it so a surface moves off center and hold it there, switch Auto Trim on for a few seconds, and disarm with the switch still on. Then connect and check the Trim column on the Servos tab. On an aircraft that is still and level the servo is already at center, so nothing visibly changes.
Auto Trim fixes a steady, always-there offset -- it isn't the right tool for a pitch change that only shows up when flaps go down. If the plane trims out fine clean but balloons (or dips) with flaps out, see Mixer → Flap-to-Elevator Compensation instead.