The open sky is a forgiving place to fly. Apart from the occasional bird or other aircraft, the obstacles are few and far between and almost always below. Flying inside buildings, or tunnels, or caves, or other confined architecture requires a somewhat different approach, even when it comes to uncrewed vehicles. A cheap drone that crashes into the walls of a cave is wasted resources. What future militaries operating underground will want is dedicated robots, built to fly in enclosed airspace.

Designed by German grone maker U-ROB, the ROBi quadcopter is a specialized machine designed to fill the small but useful niche of indoor flight.

"This includes applications such as the inspection of pipelines and combustion chambers in power plants, the inspection of chimneys and the interior of bridge structures as well as the inspection of tanks and sewage pipes," said U-ROB founder Joseph Metz in a release.

Those spaces are undoubtedly of commercial interest. They are also spaces of increasing municipal and governmental focus and military research.

DARPA is actively managing a competition where teams design autonomous machines for indoor and underground exploration. Researchers in Russia are working on remote control snake robots with redundant processing systems to scout underground spaces.

While the ROBi drone is not yet marketed at military customers, it’s design can offer some lessons for such drones bent towards military applications. Minor features, like rotors slung under the body and light cages around their perimeter, are somewhat simple to adopt. Requiring somewhat more care is the precise hand-soldering of lights, allowing its cameras and electrical connections to function even in the bumps and bounces of underground flight.

“It was with our camera lighting system that we had to develop our own solutions. In the course of the development, these solutions were constantly adapted and optimized. This was done with our development department," said Metz, describing how U-ROB’s process involved new LEDS soldered by hand on the printed circuit board to achieve the desired packaging density and miniaturization.

Such precision is unlikely to add much value for robots flying through the open sky. In the tight confines of indoor spaces, dense and deliberate sensor clustering might provide real utility.