Quadcopters may be all the rage at the moment, but they are also very easy to break due to the fact they need to be so lightweight. Crash a cheap quadcopter into a wall or have it run out of battery and come crashing to the ground, and it may never fly again. But the École polytechnique fédérale de Lausanne (EPFL) working with NCCR Robotics have a solution, which combines flexibility and magnets.
Adding any kind of protection around the frame or propellers of a drone adds weight and therefore is undesirable. Alternatively, designing a drone that's flexible may protect it from impact damage, but makes it more unpredictable during normal flight.
As IEEE Spectrum explains, the EPFL design manages to create a quadcopter that switches between rigid and flexible at appropriate times. It does this by creating the frame out of a flexible foam material, but then making the frame rigid with a detachable magnet that sits at the center.
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During normal flight, the magnet keeps the frame rigid allowing for predictable flight. However, when an impact happens the magnet detaches from the frame allowing it to become flexible and handle the impact forces without damage. As the magnet is tethered using elastic bands it doesn't go far and usually ends up reattaching to the frame once the crash is over allowing for flight to resume.
The design is inspired by insect wings, which demonstrate "dual stiffness" allowing them to transition between rigid and soft states for resilience during flight. The fact the drone is made using foam, elastic bands, and magnets to replicate this dual stiffness also means it remains relatively lightweight and cheap.
This method of dealing with impact damage works for drones, but could also be applied to other areas of robotics. It could lead to robots that are capable of moving, climbing, or interacting much more precisely and efficiently.