HANGZHOU -- A team of Chinese researchers has achieved a drone technology breakthrough by demonstrating multi-rotor flying robots that can swap tools while flying one above the other in winds strong enough to invert an umbrella.

In a study published this week in the journal Nature, engineers at Westlake University showed two quadcopters — a toolbox carrier laden with scalpels and a surgeon-type operator fitted with an extendable arm — repeatedly docking at a vertical gap with an average error of merely 8 millimeters.

When a drone hovers directly above another, its propellers create a powerful downdraft that destabilizes the lower aircraft. Tests show that at a vertical separation of just 0.6 meters, the downwash reaches over 13 meters per second, the equivalent of a Force 6 "strong breeze" on the Beaufort scale.

Using an operating system called FlyingToolbox, this collaborative flight is the first of its kind globally, and has resolved the technical challenge of achieving both close-range flight and high-precision operations simultaneously, according to the researchers.

The Westlake team devised a soft electromagnetic docking unit, which is an intelligent interface that snaps together on contact, thus boosting alignment accuracy dramatically.

In the released video clips, the system also pulled off even tougher tasks: three-drone coordination and mid-air grasping by two drones in motion.

In the future, such cooperative aerial-robot systems could take on far more intricate jobs in tasks like snatching and setting down hazardous objects, contact-based inspections, and even airborne additive-manufacturing.