The IMU consists of acceleration and angular rate sensors to determine the change in position around its own three axes. The measured values are processed in the flight control system and passed on to the motor controller as manipulated variables. Unlike fixed-wing aircraft, a multicopter cannot fly without an IMU.
The air pressure sensor measures the altitude barometrically. The further away you are from the earth's surface, the lower the air pressure becomes. This can be measured and is used to maintain the flight altitude. If there are rapid changes in air pressure due to gusts, this can also be seen in the drone's flight behaviour.
The magnetic compass is used to orientate the drone. If the compass is disturbed by electromagnetic fields, such as high-voltage power lines, this has a negative impact on the straight-line flight of the drone. The GPS-supported mode in particular will then not work safely. This uses the magnetic compass to compensate for changes in position in the correct direction, usually caused by wind.
The GNSS helps the drone to determine where it is on the earth. The more satellites there are, the more accurate the position measurement is. Data from various satellite systems such as GPS, GLONASS, Galileo or Beidou can now be used.
Acoustic sensors such as ultrasound are used by some drones to measure distance. For example, the distance to the ground can be measured for automatic landing and take-off.
Optical sensors, like ultrasound, are used for distance measurement, but also for obstacle detection or for measuring changes in position over prominent surfaces. Infrared or stereo cameras are primarily used for this purpose.
All of these sensors work together to make flying a drone easier for the pilot.
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