Despite the fact that they bang their heads against trees on a daily basis, woodpeckers don't suffer brain injuries. Inspired by the tough-headed birds, scientists have developed a fixed-wing drone that can survive frontal collisions.
Fixed-wing drones are both faster and more energy-efficient than their multi-rotor cousins, but when they hit an immovable object such as a tree, they really hit it – often resulting in irreparable damage to the aircraft. And while multi-rotors can be fitted with protective cages, the design of fixed-wing drones makes such appendages difficult to implement.
Instead, what's needed is a method for the drones to non-destructively absorb impact energy in their existing form. That's where EPFL Switzerland's SWIFT drone – aka flying robot – comes in.
Its name an acronym for "Shockproof Woodpecker-Inspired Flying Tensegrity," it does indeed incorporate a variation on structures known as tensegrities. These are generally defined as self-stabilizing structures made up of rigid (or in this case, semi-rigid) components held in place by taut cables.
A woodpecker's skull consists of a rigid beak; a flexible hyoid bone that connects the beak to the brain-containing main skull bone by wrapping around it; and a layer of spongy bone located between the hyoid and the skull bone. This arrangement, along with the relatively large amount of free space surrounding the brain inside the skull, redirects impact energy away from the brain.
In the SWIFT drone, rigid carbon fiber rods replace the beak, while bent carbon fiber strips take the place of the hyoid bone. The spongy bone is replaced by elastic cables, and the main skull is substituted by carbon fiber plates connected to carbon tubes using polylactic acid plastic brackets.
Instead of a brain, there are the electronic components, the motor, and the pusher propeller. These are suspended by rubber cables inside the "skull," with enough room for them to travel by up to 22 cm (8.7 in) upon impact.
What's more, the woodpecker-inspired, tensegrity-based, crash-mitigation tech extents to the aircraft's wings.
In woodpeckers and other birds, a network of prestressed soft connective tissue in the shoulder joints helps the bones in those joints withstand the compressive force of wing-collisions with trees or other obstacles. In the SWIFT drone, that setup is replicated by a network of 12 elastic cables and carbon fiber rods that connect each wing to the main fuselage.
Not only does this arrangement absorb the impact energy that might otherwise pull the wings right off the drone, it also absorbs energy that could damage the aircraft's "brain," thus also protecting it in the process. All together, the SWIFT drone's two tensegrity-based systems are claimed to reduce impact force by up to 70% as compared to a commercial drone of similar size and mass.
A paper on the research, which was led by Omar Aloui and colleagues, was recently published in the journal Advanced Robotics Research.
