3rd April 2017, Switzerland
Researchers at the Swiss National Centre of Competence in Research (NCCR) and the Floreano Lab at the Swiss Federal Institute of Technology in Lausanne (EPFL) have developed a new, crash resilient quadcopter, designed to withstand collisions.
The drone is made of a central case and a thin fibreglass external frame with four arms held together by four magnetic joints. As this fibreglass frame is only 0.3mm thick, it is soft and flexible, making it able to withstand collisions without permanent deformation. The four magnetic joints connect the frame to the central case and rigidly hold the frame in place during flight.
Stefano Mintchev, the lead researcher on the project, developed a quadcopter utilising the dual stiffness properties seen in insect wings. Insect wings are composed of sections made of cuticle, a stiff material that takes the load bearing portion of the wing, connected with flexible joints made of the protein resilin that have evolved to be shock absorbent and compliant. These two factors together allow insect wings to be both strong and load bearing, and compliant and durable. This principle is applied to the mechanical design of quadcopter arms, modelled after hard insect exoskeletons, that reversibly transition between stiff and soft states.
“Abstracting the biomechanical strategy of collision resilient insects' wings, the quadcopter has a dual-stiffness frame that rigidly withstands aerodynamic loads within the flight envelope, but can soften and fold during a collision to avoid damage,” researchers explain.
“The dual-stiffness frame works in synergy with specific energy absorbing materials that protect the sensitive components of the drone hosted in the central case. The proposed approach is compared to other state-of-the art collision-tolerance strategies and is validated in a 50-g quadcopter that can withstand high-speed collisions.”
During impact, the frame magnetic joints are supposed to break, meaning that the drone transitions to a soft state where the frame becomes disengaged and can safely deform without damaging itself or the inner core. Soft elastic bands ensure that the frame is held close enough in place that the magnets snap back after the collision, allowing the frame to realign and thus ensuring that the drone is once again ready to fly.
The collision resistant drone was tested by dropping it from a height of 2m whereby it completely disengaged the magnetic joints and automatically restored to its pre-crash configuration. Experiments showed that the frame of the drone withstood roughly 50 collisions with no permanent damage. On top of that, the design means that the drones can have as many rotators as desired and is not limited to a quadcopter configuration.