The compass (magnetometer) is a critical sensor for UAVs based on ArduPilot. It is responsible for determining the course, GPS coordinates and flight stability (Loiter, RTL, Auto modes). Incorrect calibration leads to:

• Drone rotation – in position hold mode.
• Navigation errors – the drone is flying in the wrong direction.
• Attitude/FBWA failures – due to data conflict with the gyroscope.

Let's look at how to properly calibrate the compass of our drone in LOGOS GCS.

When compass calibration is necessary?

• First setup of a new UAV – without calibration, the controller receives distorted data about the device's position.
• If the drone is spinning in hovering or autopilot modes.
• Does not hold course in autonomous flight mode.
• Gives errors related to the operation of the compass.

Preparing for calibration

• Avoid magnetic interference - from metal, electronic devices, power lines.
• Connect an additional power source (LiPo battery) to the drone.
• Connect the drone to the computer via USB or telemetry.
• Run the LOGOS GCS program.
• Connect to the drone from the program by selecting the network type "AUTO(SERIAL)".
• Make sure that the satellite communication sensor in the program shows a sufficient number of devices (at least 5).
• Go to "UAV settings" → "Compass".

You do not need to select a compass. The program automatically detects all of them and gives preference to an external compass over the built-in one, when one is available.

The program sends a command to the drone about the calibration completion if the procedure is successful.

How to calibrate the accelerometer in LOGOS GCS?

Calibration

• Set the "Fitness" parameter, which is responsible for the strictness of the calibration (it is enough to select 'Default').
• Click the "Calibrate" button - the first image should be outlined in white.
• Holding the drone in the horizontal plane, rotate it as shown in the 1st image in the program until it is outlined in green color.
• Holding the drone left side down, rotate it as shown in the 2nd image in the program until it is edged in green.
• Continue to change positions and rotate the drone, following the instructions in the images until they are all edged in green and the program confirms successful calibration.

Checking the results

• Connect to the drone via telemetry or USB modems.
• Open the mission planning tab.
• Make sure the compass sensor is showing the correct data.

Common problems and solutions

• Compass not healthy → check the sensor connection, reboot the flight controller.
• The drone is spinning after calibration → interference may be interfering (try again in another location).
• Calibration error → try reducing the calibration severity or calibrating outdoors, away from magnetic influence.

Conclusion

Correct compass calibration is the key to stable operation of GPS modes in ArduPilot. The procedure takes 2-3 minutes, but significantly improves the drone's behavior in autonomous flights. If problems persist, check vibrations, interference, and the physical condition of the sensor.

Tip: For multi-rotor UAVs, it is better to use an external compass mounted on the tripod (as we did) to minimize the influence of electromagnetic fields from the motors and ESC.

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