A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small enough to fit through narrow gaps and holes.

The foldable drone could be particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is an ideal job for a drone. The drone could look for people trapped inside and guide the rescue team towards them. However, in many cases, the drone would need to enter the building through a crack in a wall, a partially open window or through bars. The typical size of a drone does not allow this.

Inspired by birds

To solve this problem, researchers from the Robotics and Perception Group at the University of Zurich and the Laboratory of Intelligent Systems at EPFL (the Ecole polytechnique fédérale de Lausanne) created a new kind of drone.

Inspired by birds that fold their wings in mid-air to cross narrow passages, the new drone can squeeze itself to pass through gaps and then go back to its previous shape, all the while continuing to fly.

The researchers’ drone can also hold and transport objects along the way.

Davide Falanga, researcher at the University of Zurich and the paper’s first author, explains: “Our solution is quite simple from a mechanical point of view, but it is very versatile and very autonomous, with onboard perception and control systems.”

The ace in the hole

The Zurich and Lausanne teams worked in collaboration and designed a quadrotor with four propellers that rotate independently, mounted on mobile arms that can fold around the main frame thanks to ‘servo-motors’.

The team calls its innovative control system “the ace in the hole”. The control system adapts in real time to any new position of the arms, adjusting the thrust of the propellers as the centre of gravity shifts.

“The morphing drone can adopt different configurations according to what is needed in the field,” notes Stefano Mintchev, co-author and researcher at EPFL.

The standard configuration is X-shaped, with the four arms stretched out and the propellers at the widest possible distance from each other. When faced with a narrow passage, the drone can switch to an ‘H’ shape, with all arms lined up along one axis or to an ‘O’ shape, with all arms folded as close as possible to the body. A ‘T’ shape can be used to bring the onboard camera mounted on the central frame as close as possible to objects that the drone needs to inspect.

Autonomous rescue

In the future, the researchers hope to further improve the drone structure so that it can fold in all three dimensions. They want to develop algorithms that will make the drone truly autonomous, allowing it to look for passages in a real disaster scenario and automatically choose the best way to pass through them.

“The final goal is to give the drone a high-level instruction such as ‘enter that building, inspect every room and come back’ and let it figure out by itself how to do it,” says Falanga.

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