Using the Servo Autotrim Function (SERVO AUTOTRIM Mode)

I. Principle

SERVO AUTOTRIM is mainly used for automatic adjustment of servo center positions on fixed-wing aircraft.
Due to factors such as servo arm, control surface linkage, installation errors, uneven wing surfaces, motor torque reaction, and thrust line deviation, the aircraft may fly unstably in Manual mode and be unable to maintain straight flight.
Through SERVO AUTOTRIM mode, the flight controller can automatically adjust servo center values to compensate for these errors, allowing the aircraft to maintain straight flight when the controls are released (hands off the transmitter).
Parameters Affected by This Mode

• Only affects servos with Stabilized mixing, does not affect manual control range (1000~2000us)
  
• Affects ANGLE (stabilized mode), ACRO (manual stabilized mode), MANUAL (pure manual mode), navigation modes, etc.

II. Equipment Preparation

1) Flight Controller: This tutorial is applicable to any of the following flight controllers: SpeedyBee F405 WING APP / SpeedyBee F405 WING MINI / CoreWing F405 WING V2
2) RC Transmitter: Any CRSF protocol or SBUS protocol transmitter will work.
3) Ground Control Station Software: INAV Ground Station.
4) GPS (Optional): Method 2 requires a GPS, such as BZ-251.

III. Specific Operations

Method 1: Manually Enable AUTOTRIM
1. Enter the ground station, find SERVO AUTOTRIM on the MODES page.
2. Add channel range, bind this mode to a switch channel on the transmitter.

3. Flight Adjustment:

• Arm and take off, fly in ANGLE or ACRO mode.
• In the air, toggle the switch to enable SERVO AUTOTRIM mode.
• Stably fly for 1-3 minutes to allow the flight controller to automatically correct the servo center values.
• Switch to MANUAL mode and observe if the aircraft can maintain straight flight.
  4. Adjustment Result Processing:
• If satisfied with the adjustment: After landing, disarm directly, and the new servo center values will be permanently saved.
• If not satisfied: First turn off the SERVO AUTOTRIM switch, then disarm. The flight controller will discard the new center values and maintain the original settings.
  5. Enter the ground station "Output" page to check if the servo center values have been successfully adjusted (if not the default 1500, it has taken effect).
  Method 2: Automatic Adjustment (GPS-dependent)
  1. Enter the ground station "Configuration" page, enable the "Continuously adjust servos on fixed-wing" option (blue = on, gray = off).
  
  2. Take off and adjust:
• Arm and take off, enter ANGLE 模式, and fly steadily for 1-3 minutes.
• Switch to MANUAL 模式 and observe if the aircraft can maintain straight flight.
• If the aircraft still yaws, repeat the above steps until it can fly straight in MANUAL mode.
  3. Adjustment Result Processing:
• If satisfied with the flight controller's automatically adjusted servo center values, land and disarm. The new servo center values will be automatically saved.
• If not satisfied, land and disarm directly. You can manually adjust the servo center back to 1500 and repeat the adjustment process until flight is normal under MANUAL 模式.
  4. Enter the ground station "Output" page to check if the servo center values have been successfully adjusted (if not the default 1500, it has taken effect).

IV. Q&A

Q: After enabling AUTOTRIM, will all modes be affected?
A: Yes, after adjusting the servo center values, ANGLE, ACRO, MANUAL, and all navigation modes will be affected, but the maximum servo range (1000~2000us) will not be affected.
Q: How to determine if AUTOTRIM was successful?
A: Enter the ground station "Output" page and check if the servo center values have changed (e.g., 1500 → 1570us). Switch to MANUAL mode and observe if the aircraft can fly straight without input.
Q: What if the aircraft still yaws after adjustment?
A: Repeat the AUTOTRIM operation until the aircraft can fly stably straight in MANUAL mode. If yawing still persists, manual adjustment of servo linkages or mechanical structures may be necessary to avoid hardware errors.

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