Since the beginning, the development of quadcopters and drones has been
strongly influenced by sensors in combination with microprocessors.
These flight systems would not be feasible without sensors, because
gyros, acceleration sensors and inertial measurement units, for example,
are absolutely necessary to make them fly. These are used for axis
control. Others, such as the electronic compass, the air pressure sensor
or GPS, make control considerably easier for the pilot. Together with
sophisticated software, additional sensors such as ultrasonic, infrared
or cameras allow additional functions such as automated take-offs and
landings, obstacle detection or object tracing. All these sensors and
their physical principles are explained in this booklet and their use
and possibilities in quadrocopters and drones are discussed.