This drone is barely visible, but it’s deafeningly loud
Researchers at Northwestern University are using motion blur to make a drone virtually invisible whilst in flight. It could be used for covert surveillance or to create hologram effects.
Researchers at Northwestern University in the US state of Illinois have developed a virtually invisible drone. Instead of using camouflage patterns, transparent materials or mirror systems, they have relied on the effect of motion blur: the human eye cannot perceive very fast movements. This makes the object appear blurred or even transparent. You’ll be familiar with this principle from aeroplane propellers and helicopter rotors.
In the drone’s prototype, the «Phantom Twist», it is not just the rotor that rotates, but the entire aircraft. At 15 to 25 revolutions per second, it appears in flight as nothing more than a blurred speck and can therefore easily be overlooked.
At first glance, the palm-sized drone does not look like something capable of flight. It is propelled by a three-bladed propeller. The motor is connected to the control board, the batteries and a counterweight via several delicate struts. The team used a computer model to develop the prototype: It calculated 20,000 drone designs that would enable stable flight. An AI then analysed these designs in terms of their visibility in flight and, through several feedback loops, generated the optimal design for a prototype.
Almost invisible, but uncomfortably loud
The researchers envisage their robot being used, for example, as an inspection device. They state that animals, humans and «other systems» behave differently when they perceive a robot. Observations may therefore be distorted. «Phantom Twist» is designed to observe unobtrusively and thereby collect valid data.
To carry out its task, the «Phantom Twist» can theoretically carry a payload of up to 40 grammes. A so-called line scan camera could continuously capture a three-dimensional image of the surroundings thanks to its rapid rotation. However, the drone could also be used as a flying display: equipped with LEDs, it could generate a floating, three-dimensional hologram at up to 25 FPS, much like a flip book.
At present, the device is barely visible in the air, but all the more audible for it: the drone emits an unpleasantly loud whistling sound. This puts a spanner in the works for unnoticed observation. In their paper, the research team state that reducing the noise level has not been a priority so far. For future development, the authors suggest specifically optimising the propeller for quieter operation. Alternative propulsion concepts without moving parts could also make the drone quieter.
Up to ten minutes of precise hovering
Unlike helicopters and quadcopters, the «Phantom Twist» cannot take off from a standstill. A manually operated launch device, which can be seen in the video, sets the drone spinning until it reaches the rotational speed required for stable operation. It can then fly autonomously.
According to the research paper, the drone’s position can be controlled with an accuracy of up to three centimetres. However, tests in strong winds have not yet been carried out. Currently, a single battery charge keeps the «Phantom Twist» airborne for up to ten minutes.
Feels just as comfortable in front of a gaming PC as she does in a hammock in the garden. Likes the Roman Empire, container ships and science fiction books. Focuses mostly on unearthing news stories about IT and smart products.
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