This drone is barely visible, but deafeningly loud
Researchers at Northwestern University are using motion blur to make a drone almost invisible in flight. It could be used for unobserved observations or hologram effects.
Researchers at Northwestern University in the US state of Illinois have developed a nearly invisible drone. Instead of camouflage patterns, transparent materials, or mirror systems, they rely on the effect of motion blur: the human eye cannot perceive very fast movements. This makes the object appear blurred or even transparent. You know this principle from airplane propellers and helicopter rotors.
In the prototype of the drone, the "Phantom Twist", not only the rotor rotates, but the entire aircraft. At 15 to 25 revolutions per second, it appears only as a blurred spot in flight and can therefore be easily overlooked.
At first glance, the palm-sized drone does not look like a flying object. It is carried by a three-bladed propeller. The motor is connected to the control board, batteries, and a counterweight via several delicate struts. For the development of the prototype, the team used a computer model: It calculated 20,000 drone designs that allow for stable flight. An AI then analyzed these designs for their visibility in flight and, in several feedback loops, generated the optimal design for a prototype.
Almost invisible, but unpleasantly loud
The researchers see their robot, for example, as an inspection device. They state that animals, humans, and "other systems" behave differently when they perceive a robot. Observations can therefore be distorted. "Phantom Twist" is intended to observe inconspicuously and thus collect valid data.
To perform its task, the "Phantom Twist" can theoretically carry up to 40 grams of payload. A so-called line camera could continuously capture a three-dimensional image of the environment through rapid rotation. The drone could also be used as a flying display: equipped with LEDs, it could create a floating, three-dimensional hologram like a flip book at up to 25 FPS.
Currently, the device is barely visible in the air, but all the more audible: the drone emits an unpleasantly loud whistling sound. This thwarts unnoticed observation. The research team states in its paper that reducing the volume has not been a priority so far. For future development, the authors suggest optimizing the propeller specifically 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, shown in the video, sets the drone in rotation until it reaches the speed for stable operation. Then it can fly independently.
According to the research, the drone's position can be controlled with an accuracy of up to three centimeters. However, tests in strong winds have not yet taken place. Currently, one battery charge keeps the "Phantom Twist" in the air for up to ten minutes.
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