The prototype drone proved to be extremely energy-efficient: it spent more than 24 minutes in the air on a single charge. The maple fruit is a favourite of many children, and when thrown into the air it spins downwards for a long time, but no one had any idea what a great drone could be made from its construction.
The IEEE Spectrum site spotted a drone developed by the City University of Hong Kong, whose lift, unlike conventional drones, is provided not by four rotors but by its own rotation, which is roughly 200 revolutions per minute, according to an article in the South China Morning Post. Two rotors on the wingtips, powered by tiny electric motors, are responsible for the rotation and can be controlled by varying the thrust of the rotor separately. The drone has a wingspan of 60 centimetres, but weighs just 42.5 grams, including its 650mAh battery, which allows it to charge for more than 24 minutes in the air.
Continuous rotation may not seem to be the most advantageous for some instruments, but researchers have found that most sensors do not care if they rotate, and for some devices – such as radars – it can even be beneficial. Only the cameras can have some difficulty with rotation, but the researchers overcame this by matching the frame rate of the monocopter’s camera to the rotation rate, so that they could extract four separate live videos from the single camera fitted, each with a frame rate of 3.5 fps. The drone is thus able to provide camera footage from essentially every direction simultaneously.
A drone rotating on its own axis is rare. However, the fact that it does not need a separate microprocessor for stabilisation compared to similar quadcopters is a design advantage, and the flight above was accomplished without this component. In addition, the researchers observed that their drone spent on average twice as much time in the air as its more conventionally built counterparts of similar performance. That said, its creators believe future versions of the drone could be suitable for reconnaissance or surveillance missions. The researchers published a paper summarising their experiences with the drone in the scientific journal Science Robotics.