Airspeed Sensors¶
Airspeed sensors are highly recommended for fixed-wing and VTOL frames. They are so important because the autopilot does not have other means to detect stall. For fixed-wing flight it is the airspeed that guarantees lift — not ground speed!
Hardware Options¶
Recommended digital airspeed sensors include:
- Based on Pitot tube
- MEAS Spec series (e.g. MS4525DO, MS5525)
- mRo I2C Airspeed Sensor JST-GH MS4525DO (mRo store)
- Digital Differential Airspeed Sensor Kit (Drotek).
- EagleTree Airspeed MicroSensor V3 (eagletreesystems)
- Sensirion SDP3x Airspeed Sensor Kit
- Holybro Digital Air Speed Sensor
- Based on Venturi effect
- TFSLOT Venturi effect airspeed sensor.
All the above sensors are connected via the I2C bus/port.
:::note
Additionally, the Avionics Anonymous Air Data Computer can be connected to the CAN bus to determine not only high-accuracy airspeed, but also true static pressure and air temperature via onboard barometer and an OAT probe.
:::
Configuration¶
Enable Airspeed Sensors¶
Airspeed sensor drivers are not started automatically. Enable each type using its corresponding parameter:
- Sensirion SDP3X: SENS_EN_SDP3X
- TE MS4525: SENS_EN_MS4525DO
- TE MS5525: SENS_EN_MS5525DS
- Eagle Tree airspeed sensor: SENS_EN_ETSASPD
You should also check ASPD_PRIMARY is 1 (see next section - this is the default).
Multiple Airspeed Sensors¶
:::warning Experimental Using multiple airspeed sensors is experimental. :::
If you have multiple airspeed sensors then you can select which sensor is preferred as the primary source using ASPD_PRIMARY, where 1, 2 and 3 reflect the order in which the airspeed sensors were started:
0: Synthetic airspeed estimation (groundspeed minus windspeed)1: First airspeed sensor started (default)2: Second airspeed sensor started3: Third airspeed sensor started
The airspeed selector validates the indicated sensor first and only falls back to other sensors if the indicated sensor fails airspeed checks (ASPD_DO_CHECKS is used to configure the checks).
The selected sensor is then used to supply data to the estimator (EKF2) and the controllers.
Sensor-specific Configuration¶
Other than enabling the sensor, sensor-specific configuration is often not required. If it is needed, it should be covered in the appropriate sensor page (for example TFSLOT > Configuration).
The specific configuration for sensors that do not have a separate page is listed below:
- Sensirion SDP3X: CAL_AIR_CMODEL (provides overview of required settings), CAL_AIR_TUBED_MM, CAL_AIR_TUBELEN.
Calibration¶
Airspeed sensors should be calibrated by following the instructions: Basic Configuration > Airspeed.