Robotic arms and 3D printing gantries can already be found on construction sites – albeit mostly as heavy, permanently installed systems on the ground. They quickly reach their limits on rough terrain or at great heights. A team led by researchers from the Laboratory of Sustainability Robotics at Empa and EPFL has therefore investigated how aerial robots could be used as autonomous construction platforms in the future. In the cover story of the current issue of Science Robotics, the researchers show the state of the art and the potential of this upcoming technology. The advantage is obvious: Construction drones can reach places that are inaccessible to conventional machines, be it in the mountains, on rooftops, in disaster areas or even on distant planets. They also do not require a fixed construction site, can be deployed in swarms, and therefore offer a high degree of flexibility and ease of scalability. At the same time, they could shorten transportation routes, reduce material consumption and make construction sites safer.

Repairs and operations in extreme situations

Aerial robots are particularly suitable for disaster relief operations – for example, in flooded or destroyed regions where conventional vehicles can no longer get through. Aerial robots could transport building materials and autonomously erect emergency shelters. Their use is also promising for repairs in places that are difficult to access. They could autonomously detect and repair cracks on high-rise facades or bridges without scaffolding. “Existing robotic systems on the ground often weigh several tons, take a long time to set up and have a limited working radius,” explains Yusuf Furkan Kaya, the lead author of the study, from the Sustainability Robotics Laboratory at Empa and EPFL. "Construction drones, on the other hand, are light, mobile and flexible – but so far they only exist at low technology readiness levels. They have yet to be used for industrial purposes."

In fact, there are already numerous academic prototypes that demonstrate different methods of airborne construction, from the placement of individual building elements and the tensioning of cable structures to the layer-by-layer printing of building materials. At Empa, for example, flying robots have been programmed to work together as a team to print materials layer by layer for the construction or repair of structures.

Interplay of technology, material and design

The potential of drones is disruptive – they can theoretically fly and build anywhere, if energy supply and material transportation are guaranteed. And they are easily scalable: In the event of a disaster, hundreds of aerial robots could immediately set up temporary infrastructure in remote areas.

At the same time, future construction with drones faces new challenges. According to the researchers, a key hurdle is the interdisciplinary nature of the technology: Aerial Additive Manufacturing (Aerial AM) requires simultaneous progress in three areas: robotics, materials science and architecture. Mirko Kovac, Head of the Laboratory of Sustainability Robotics at Empa and EPFL, describes the interplay as follows: "A drone may be able to fly precisely, but without lightweight, stable and processable materials, it cannot develop its full potential. And even if both are available, building designs must be adapted to the limited precision of the aerial robots to enable load-bearing structures."

Complementing existing robots

In addition to this cross-disciplinary coordination, there are other technical hurdles within robotics, such as limited flight time, payload or autonomy. The study therefore presents an autonomy framework in five stages – from simple flights along a route to full independence, in which aerial robots can analyze the construction environment, detect errors and even adapt the design in real-time. According to Yusuf Furkan Kaya, this is not only a theoretical model but also a clear development plan. “Our goal is to have aerial robots that understand what material they are building with and in what environment, and intelligently optimize the resulting structure during construction.”
For the time being, Aerial AM remains a complementary solution to existing ground-based robotic systems. Drones' energy consumption is currently eight to ten times higher, and their construction volume is also limited. The researchers, therefore, recommend a combined approach: While conventional systems build the lower areas of a structure, drones take over from a certain height and bring their strengths in flexibility and range to bear there.


Box: DroneHub

The new DroneHub in Empa's NEST research and innovation building plays a key role for Aerial AM. This multi-environment robotic testbed was designed as a bridge between the laboratory and industrial applications. “Construction drones can be tested here under real-world conditions, further developed and brought to market maturity,” says Mirko Kovac, who heads the NEST unit developed in collaboration with Imperial College London. The DroneHub supports the new joint professorship for Sustainability Robotics between Empa and EPFL and is central to the extended partnership with Imperial College London. This infrastructure, which is unique in Europe, provides Empa with a platform on which flying construction machines can be tested outside the laboratory for the first time. The first field trials are planned for this year.