Sensor Calibration

Introduction

The Vertex One contains multitude of sensors, like accelerometers and a magnetometer which in certain cases may require calibration.

Magnetometer

To increase navigation accuracy and offer sensor redundancy the Vertex One contains two magnetometers:

  1. Internal magnetometer (placed in the drone’s body)
  2. External magnetometer (placed on the magnetometer bracket)

The magnetometer measures magnetic field around Vertex One including earth’s magnetic field. This measurement, in principle like a navigation compass, is one of the sensor inputs to determine the flight orientation of Vertex One. When experiencing issues with position hold, specifically circling behavior (often referred to as 'toilet bowling'), calibration might be required.

The measured Earth’s magnetic field is variable depending on the location, while it can also be (locally) disturbed by the presence of:

  1. Large (metallic) structures, e.g. tanks, poles, masts, cranes
  2. Power distribution net, e.g. high-voltage lines
  3. Other electromagnetic fields, e.g. in the proximity of transmitters, broadcasting devices or other electronic devices.

Depending on the nature of these, the disturbances might cause intermittent orientation readout inaccuracies or a constant readout inaccuracy or a readout drift. For these environmental influences the sensor can not be calibrated.

A different magnetic declination can however be set using the parameters. Ensure that this value is set correctly before re-calibrating the magnetometer.

Calibration is advised in the following situations:

- Adding a custom payload to the Vertex One which may influence the body fixed magnetic field.
- Experiencing circling behavior in position hold without any custom payload in an open field (e.g. no external magnetic disturbances).
- Experiencing non-forward flying in manual position mode and commanding a forward velocity using the RC.
- The Vertex One does not pass the stage of magnetometer initialization after start-up in a magnetic disturbance free environment. This indicates that the current calibration is no longer valid.
- The magnetometer is repaired or replaced.

Magnetometer calibration procedure

Caution

Only perform this calibration in a relevant environment (outdoors) without any obvious local disturbances to the earth magnetic field (e.g. away from metallic structures and powerlines). Do add any custom payload to the drone which will be used during operation and may influence the body magnetic field.

Caution

Ensure that the person performing the re-calibration has by them no devices that might cause disturbance of the magnetic field such as a mobile phone or a watch.

Required tools:

  • Vertex One with propellers fixed using the foam prop guards.
  • Windows computer with Cerebra Lab installed.

  • USB cable or WiFi connection to the Vertex.

  • Download the magnetometer calibration application here. Make sure to get the correct version based on your Vertex One gen type and Vertex One software version.

  • Start Cerebra Lab.
  • Power on the Vertex and connect through Wi-Fi or using a USB cable.
  • Stop the current application by holding the pause button.
  • Upload the calibration application to the Vertex One using the following instructions.

If indoors, first power off the Vertex, go outdoors to a location with minimal magnetic disturbance and power on the Vertex again to continue calibration. If already outdoors, make sure to disconnect the USB cable and move away from the computer before continuing the calibration process.

Calibration sequence

Once movement starts the indicator LEDs will flash blue. During the flashing data is gathered for the calibration, with too little movement the indicator LEDs turn purple again. Repeat the following sequence until the indicator LEDs are solid blue. After a few seconds the indicators LEDs should turn green indicating the the calibration is successfully written to the memory. For the calibration visualize that the Vertex needs be have been pointed towards as many directions in a 3D sphere. An advised sequence is:

  1. Rotate the drone 360 degrees with 'pitch' maneuvers while rotating around yourself
  2. Hold the drone from the carbon side rods (90 deg roll) and 'yaw' the drone around this axis
  3. Rotate the drone around its diagonal axis ~90 degrees back and forth.

Post calibration

After the calibration the flight controller for your Vertex One generation must be downloaded from the release page for your release and uploaded again to the Vertex. The flight controller uses the latest calibration data at startup.

Troubleshooting

The LED indicators are rapidly flashing red, what is going wrong?

Verify that the external magnetometer is connected and working properly. The signals in Cerebra Lab Workspace named 'main_mag_status' and 'secondary_mag_status' should both be zero. Restart the model if the external magnetometer was not connected to try again. Contact Avular if this issue persists.

Accelerometer

Accelerometer Calibration Indication

Accelerometer measures acceleration. As this gravitational acceleration is slightly different across the Earth, the sensor might have slight offsets in the measurement. Consider re-calibrating the accelerometer when you are:

  • Experiencing large drifts while flying with the default parameters for mass and center of gravity without any custom payload constant throughout the flight.

Accelerometer Calibration Procedure

Please contact Avular support if you think calibration is required.