“BEWARE: WILD ROBOTS AHEAD” reads the sign on the cage. Inside, a hexacopter – a drone with six rotors – hovers menacingly. A quadcopter – with four – rests on the ground.

They aren’t really wild robots, of course, and the test arena isn’t much of an ecosystem, but the quadcopter in particular has a rather special skill: it can build its own nest out of foam. In effect, it’s the world’s first flying 3D printer. One day such drones might work together to help remove waste from nuclear sites or help patch up damaged buildings.

Inspired by the swiflets that build nests using their own saliva, Mirko Kovac of Imperial College London and his team wanted an aerial robot that could make structures. The quadcopter carries two chemicals which create polyurethane foam when mixed, and a printing module to extrude the foam. As we watch, it takes off and hovers over a box in the arena, before lowering an arm and squirting the foam on to the box.

[SOURCE](http://www.newscientist.com/article/mg22229683.900-flying-3d-printer-could-seal-off-nuclear-waste.html#.U3C_u_ldV2B)