Robots build new hanging gardens

Working with Müller Illien Landscape Architects, Timbatec and other partners from industry and research, researchers from the group led by ETH architecture professors Fabio Gramazio and Matthias Kohler are creating a green architectural sculpture for the Tech Cluster Zug. Soaring to a height of 22.5 metres, the structure will consist of five geometrically complex wooden pods that are slightly offset from each other and supported by eight thin steel pillars. The sculpture, named after the Babylonian queen to whom the ancient Hanging Gardens of Babylon have been attributed, is being designed and built using innovative digital methods that were developed as part of the project.

AI proposes a clever design

In the conventional design process for projects like this, architects try to take the different requirements of a building or structure into account in its design, and then adjust that design until all the requirements are met in the best way possible. Not so with Semiramis: a custom machine learning algorithm, developed in collaboration with the Swiss Data Science Center, presented the researchers with sophisticated design options. The proposals differed as to the shapes of the pods and their spatial arrangement relative to each other. They also highlighted how each design affected individual target variables, such as irrigation for the pods. “The computer model lets us reverse the conventional design process and explore the full design scope for a project. This leads to new, often surprising geometries,” says Matthias Kohler, Professor of Architecture and Digital Fabrication at ETH Zurich.

In the Immersive Design Lab, an augmented reality laboratory on the Hönggerberg campus, the researchers were able to explore the designs in three dimensions and fine-tune them together in real time. Software developed jointly with ETH’s Computational Robotics Lab makes adapting the designs of the wooden pods easy: for example, if the scientists move a single point within the geometry of one of the pods, which are composed of about 70 wooden panels, the software adjusts the entire geometry. At the same time, the software takes into account the relevant manufacturing parameters, such as a panel’s maximum possible weight, meaning it always generates the most efficient and most load-bearing configuration.

A delicate dance for the highest precision

The best design is currently being manufactured in the Robotic Fabrication Laboratory at ETH Zurich. Always in sync, four suspended robotic arms each pick up the wooden panel assigned to them, perform a high-precision dance and finally put the panels into place according to the computer design. An algorithm calculates the movements of the robots in such a way that no collisions occur during execution. Once the machines have placed their four panels next to each other, craftspeople first temporarily join them before gluing them together with a special casting resin. Each of Semiramis’s five wooden pods comprises between 51 and 88 of these wooden panels.

In contrast to traditional wood construction, robotic manufacturing has several advantages: for one thing, the robots relieve humans of the heavy lifting and precise positioning; for another, the assembly process requires no costly, resource-intensive substructures.

A symbol of collaboration

Robotic prefabrication is currently running at full speed. Individual pod segments are being shipped to Zug by lorry on a regular basis, where the architectural sculpture will be erected and finally planted out in spring 2022. Starting that summer, people will be able to view the wooden structure from the ground or from nearby buildings and catch a glimpse of the greenery in the pods.

For Kohler, meanwhile, the project has already proven its value: “Semiramis has been a beacon project for architectural research, bringing together people inside and outside ETH and advancing the key research topics of the present, such as interactive architectural design and digital fabrication,” he says.