Sensor Hardware & Setup

This section describes the mandatory and optional sensors and their setup/configuration.

Overview

PX4-based systems use sensors to estimate vehicle state, which is needed for stabilization and to enable autonomous control. Vehicle state information includes: position/altitude, heading, speed, airspeed, orientation (attitude), rates of rotation in different directions, battery level, and so on.

PX4 minimally requires a gyroscope, accelerometer, magnetometer (compass), and barometer to measure the above states. Fixed-wing and VTOL-vehicles should also include an airspeed sensor. A GPS or other positioning system is needed to enable all automatic modes, and some manual/assisted modes.

Pixhawk Series flight controllers already have the minimum set of sensors (other controller platforms often do too). Additional/external sensors can be attached to the controller — an external GPS and compass are recommended, along with an airspeed sensor for VTOL and Fixed wing vehicles.

Sensor Topics

Mandatory (included in Pixhawk series FCs):

• Accelerometer — Measures changing acceleration.
• Gyroscope — Measures orientation.
• Magnetometer (Compass) — Measures heading/direction. External compass recommended!
• Barometers — Measures altitude (via air pressure).

Recommended:

• Airspeed Sensors — Measures airspeed. Highly recommended for VTOL and Fixed-wing as they are the only mechanism to detect stall.
• GNSS (GPS) — Measures global position. Needed for missions, and some other automatic and manual/assisted modes.
• RTK GNSS (GPS) — GNSS with centimetre-level accuracy. Some setups also allow heading to be determine from GNSS rather than a magnetometer.

Optional:

• Distance Sensors (Rangefinders) — Measures distance to target. Aids landing, object avoidance, and terrain following.
• Optical Flow — Estimates velocity using a downward facing camera and a downward facing distance sensor. Enables a more accurate position lock than GPS alone, and can be used indoors when no GPS signal is available.
• Tachometers (Revolution Counters) — Only used for logging.

Other optional:

• IMU/Compass Factory Calibration — Save calibration settings to persistent storage.
• Sensor Thermal Compensation — Compensate sensors for temperature variations.