MIT Invents A Way To 3-D Print Liquid Robots

Thanks to printable hydraulics, these robots are ready to walk, crawl, or roll from the second they finish printing.

Daniela Rus and Robert MacCurdy, two roboticists at MIT’s Computer Science and Artificial Intelligence Lab, have a dream. One day, they want you to be able to download a robot, 3-D print it at home, and have it walk right off the print bed when it’s done.


That dream is still a little ways off, but Rus and MacCurdy have just taken a big step toward making it happen. Working with Ph.D. candidate Robert Katzchmann and Harvard undergraduate Youbin Kim, the pair have developed a new method of 3-D printing that makes it possible to create half-solid, half-liquid robots. Throw a battery in, and they’re ready to walk, because they’ve been printed with fully functioning hydraulics–the same technology you’ll find in your car.

Admittedly, “half-solid, half-liquid robots” sounds like MIT’s figured out how to 3-D print Terminator 2‘s T-1000s. What we’re actually talking about is a little more mundane: A method for 3-D printing robots with working hydraulic systems like gear pumps, bellows, rotating crankshafts, and more. With this technique, you can 3-D print a six-legged walking robot in a single print job—the only thing you’d need to do to make it work is add a circuit board and power source at the very end. Otherwise, the robot comes out totally preassembled.

Like many 3-D printing technologies, MIT’s technique works by depositing individual droplets of photopolymer on a print bed, layer by layer. Each layer of this material is then cured by blasting it with high-intensity UV light, which hardens it. What makes MIT’s approach different than similar printers, though, is that it mixes in droplets of non-curing material–which never hardens–as it prints. By switching between the two materials within a print job, the printer can create functional hydraulic systems: For example, a crankshaft that pumps fluid to move a robot’s legs. Using this technique, CSAIL already 3-D printed a working hexapodal robot in just 22 hours, a duration that should come down over time.

Rus and MacCurdy hope that their discovery will dramatically reduce the headache of designing new kinds of robots. “Right now, robots are very time-consuming and expensive to make and require a great deal of skill to assemble,” says MacCurdy. “So roboticists make all sorts of decisions throughout the design process to minimize the complexity of the finished robot.” If you can 3-D print a robot with working hydraulics, though, you don’t have to make the same kind of trade-offs due to complexity.

Roboticists can design incredibly intricate robots and then rapidly prototype them without having to worry about actually assembling the damn things. “Because the cost of making a robot with 2 legs or 20 legs is pretty much the same [with our technique], we hope printable hydraulics will allow the proliferation of totally new robot designs,” he says.

Eventually, MacCurdy says that he thinks printable hydraulics could open the door to the automated design and fabrication of robots. So instead of humans designing robots to solve a problem, humans will just tell an algorithm what problem they want to solve–and a few hours later, a custom robot walks off the 3-D printer, ready to get to work.


All CSAIL needs to figure out to get there is how to 3-D print circuit boards and power sources, something Rus says they’re already working on. The future of robotics, she says, is going to be a lot like the App Store: For any given task you want to accomplish, there’s a bot for that.