ETH Zurich builds FlexiQuad, a soft-frame quadcopter prototype that survives 25 km/h collisions

Researchers at ETH Zurich have built FlexiQuad, a quadcopter prototype with a soft ring-shaped frame and no central body, according to DEV.UA, citing Tech Xplore. The rotors, batteries and control module are distributed evenly along the frame. The drone was developed by Luca Girard and Stefano Mintchev at the Environmental Robotics Laboratory of ETH Zurich. The authors have filed a patent application, and the project was nominated for the Spark Award dev.uaDEV.UAdev.uaOpen source ↗.

Soft ring frame instead of a rigid body

For more than a century, quadcopters have followed one basic layout: four arms with propellers extend from a rigid central body. This layout suits precise flight, but it is sensitive to unplanned contact, and even a minor hit against a wall can destabilize or destroy the aircraft dev.uaDEV.UAdev.uaOpen source ↗.

In FlexiQuad the frame deforms on impact and absorbs most of the collision energy. The frame is not flexible in every direction. Girard says the team drew on birds and insects, and on how stiff their wings are in different directions. The frame bends easily in the horizontal plane, where deformation is needed, and stays rigid vertically, so the rotors can transmit thrust efficiently dev.uaDEV.UAdev.uaOpen source ↗.

The design is modular and inexpensive: the body materials cost less than 15 Swiss francs. The flat frame elements fold compactly when disassembled, and Girard transported one of the prototypes in an ordinary suitcase dev.uaDEV.UAdev.uaOpen source ↗.

Test results and open problems

According to Girard, the drone reaches 80 km/h, and its linear and angular acceleration is comparable to that of rigid drones. In tests, FlexiQuad deliberately flew into obstacles at up to 25 km/h. The frame deformed briefly, which reduced the load, and the drone continued flying. The same flexibility is used for handling cargo: the drone carried a soft first-aid kit and lifted a load heavier than itself dev.uaDEV.UAdev.uaOpen source ↗.

The authors name possible uses in confined spaces: inspecting ship ballast tanks and other hard-to-reach structures, scouting inside collapsed buildings by squeezing through narrow openings, and taking measurements in dense forests where branch collisions are a risk dev.uaDEV.UAdev.uaOpen source ↗.

Before leaving the laboratory, FlexiQuad needs reliable orientation and autonomous navigation. After a collision, vibrations of the flexible frame blur the camera images, which complicates the work of the sensors. The researchers took insect reflexes as inspiration: the drone is currently being trained to stabilize itself after an impact using onboard motion sensors, and only then to return to autonomous flight. The team is also studying whether the frame's own vibrations and deformations could serve as an additional feedback channel for the flight control system dev.uaDEV.UAdev.uaOpen source ↗.