What’s possible with 3D printing is largely driven by two things: How patient you are, since printing large or complex structures can take a while, and what kind of build volume you have to work with. Most 3D printers are boxes, and inside those boxes are smaller boxes, and inside those boxes are the area in which a thing can be printed. If your thing is larger than that box, you’ve either got to print it in pieces that can be assembled later, buy yourself a new printer, or give up entirely.

You can certainly 3D print very large things, but there are still usually build volume constraints. We’ve seen examples of robot arms that can print anywhere they can reach, as well as gantry systems that can print structures like houses, as long as the structures are slightly smaller than they are. The way to avoid constraints like these is to have a robot that can both 3D print things and move around, and once you’ve decided to go that route, there’s no reason not to use multiple robots to speed things along. Roboticists at Nanyang Technological University in Singapore have, for the first time (as far as they know), performed “the actual printing of a single-piece concrete structure by two mobile robots operating concurrently.”