A collision with a wall is usually enough to destabilize and bring down a drone. Its four propellers are attached to a rigid structure that does not handle contact well. At ETH Zurich, researchers chose a different solution: allowing the aircraft to deform when it encounters an obstacle.
Their prototype, called FlexiQuad, looks like a large ring fitted with four propellers. It has no rigid central body. The batteries and control components are distributed around its frame. During an impact, the frame briefly bends and absorbs some of the shock before returning to its original shape.
The FlexiQuad drone has four rotors and a deformable body.
Image: Luca Girardi / ETH Zurich
That said, this drone is not flexible in every direction. Its frame can bend sideways but remains sufficiently rigid from top to bottom. This rigidity should allow the propellers to lift and steer the aircraft. The researchers drew inspiration from the wings of birds and insects, which can bend without losing their effectiveness.
Tests showed that FlexiQuad could continue flying after hitting obstacles at around 25 km/h. This speed is comparable to that of a cyclist riding quickly in a city. And its flexibility does not prevent it from moving fast: in flight, the prototype can reach 80 km/h.
This capability could change how cluttered environments are explored. In a collapsed building, for example, a drone sometimes has to pass close to rubble to search for people. A branch or an undetected wall could then bring its mission to an end. With a frame that can absorb contact, some passages would become less risky.
Another distinctive feature is that the ring can also be used to grasp objects. The researchers have already had it transport and then drop off a soft first-aid kit. In another test, the drone lifted a load heavier than itself.
FlexiQuad is still a laboratory prototype, however. To operate independently in the field, it will need to detect obstacles more effectively and regain a stable trajectory after each impact. Vibrations in its frame can notably disrupt images from its camera. The team is working on controls capable of automatically correcting these movements using the onboard sensors.