Barometer altitude fluctuates

1. Symptoms

• Altitude oscillates by a fraction of a metre to metres while the robot is still or hovering.
• Steps when a door closes, a fan starts or the sun hits the board.
• Slow drift over minutes.

2. Possible causes

• Airflow over the port: wind, propwash, a cooling fan, or a vehicle’s motion.
• Enclosure pressure: a sealed case whose internal pressure changes with temperature or airflow.
• Temperature changes at the sensor (sunlight, self-heating).
• Weather: real changes in atmospheric pressure over hours.
• Noise: unfiltered readings at a high rate.
• Conversion error: a wrong reference pressure or a constant offset.

3. Measurements to collect

• Pressure (Pa) over time with the robot still, with fans and motors on and off.
• Sensor temperature.
• Noise (standard deviation) in a still, closed room.
• Pressure inside and outside the enclosure.

4. Diagnostic commands

Commands are not executed by the site’s automated tests (they need a ROS 2 Jazzy installation or the robot).

ros2 topic echo /pressure --field fluid_pressure
ros2 bag record /pressure /temperature

5. Step-by-step investigation

1. Record still pressure in a calm room and compute the noise. This is the floor.
2. Switch fans and motors and watch for steps (airflow).
3. Warm the sensor (hand, heat source) and look for a change.
4. Check the enclosure venting and the port position.
5. Check the conversion: altitude from pressure needs a reference (sea-level or a ground reading at start); weather moves the reference.
6. Filter and fuse with the IMU or GNSS instead of using it raw.

6. Corrective actions

• Move the port away from airflow and shield it with foam or a baffle; vent the enclosure to a still region.
• Isolate the sensor from heat sources and sunlight.
• Low-pass filter, and fuse with the IMU vertical acceleration.
• Re-zero at start and for relative height use differences only.
• Compensate temperature as the datasheet specifies.

7. Validation after the fix

• Still-air noise is within the datasheet figure.
• No steps when fans, motors and doors change state.
• Relative height error over a flight or run is within the requirement.

References

• sensor_msgs definitions (Jazzy): ros2/common_interfaces, read 2026-11-05. FluidPressure: absolute pressure in pascals plus a variance (0 means unknown).
• Related guide: inertial and positioning sensors guide.