IEEE Sens. J. (2019)

Monocopters — small unmanned aerial vehicles with a single rotor — could be of use in agriculture, surveillance and package delivery. To generate lift for take-off and hovering, monocopters rotate along their vertical axis, generating turbulent air flow. Accurate measurements of the rotation speed and air flow during flight are thus essential for controlling their navigation. However, current approaches for measuring the rotation speed in drones, such as magnetic sensors, image processing microcontrollers or sophisticated inertial measurement units, are bulky and expensive. Current air-flow sensors are also problematic: anemometers are costly and pitot tubes are unreliable in monocopters. Shaohui Foong and colleagues at the Singapore University of Technology and Design have now developed lightweight, compact and low-cost sensors that can measure rotation speed and air flow in a monocopter.

Credit: IEEE

The researchers integrated a microelectromechanical system (MEMS)-based barometric sensor and a sensing element (a steel sphere) into a silicone elastomer in order to create a soft, tactile sensor. During rotation, the sphere pulls away from the centre of the sensor, changing the pressure inside the elastomer. This change is measured by the barometric sensor and can be used to extract the rotation speed. At the same time, the air flow causes a compression of the elastomer and can be monitored.

During tests under controlled conditions, the sensors could measure rotation speeds up to 10 hertz and air-flow speeds up to 60 metres per second, performing better than a commercial inertial measurement unit and anemometer, respectively. However, tests on a custom-built monocopter were carried out at a rotation speed of 5.1 hertz and air-flow speeds below 20 metres per second.