Building robots out of liquid may streamline manufacturing

Add this to the list of feats 3D printers can perform: Fully functioning robots made out of liquid.

MIT's Computer Science and Artificial Intelligence Lab (CSAIL) is 3D printing robots.

Not robot parts, but robots. Working machines that function autonomously.

The idea is that one of the biggest barriers to long-promised robotic revolution is in manufacturing. Robots have a lot of parts, and manufacturing them is expensive and highly specialized.

But 3D printers are getting more and more dynamic and could make traditional assembly processes obsolete, even for complex machines.

In a new paper, researchers at CSAIL present a technique for 3-D printing robots that involves printing solid and liquid materials at the same time.

The new method allows the team to automatically 3-D print robots in a single step, with no assembly required, using a commercially-available 3-D printer.

"Our approach, which we call 'printable hydraulics,' is a step towards the rapid fabrication of functional machines," says CSAIL Director Daniela Rus, who oversaw the project and co-wrote the paper. "All you have to do is stick in a battery and motor, and you have a robot that can practically walk right out of the printer."

The proof is in the 3D-printed pudding. To test their concept, researchers 3-D printed a crawling six-legged robot actuated by 12 hydraulic pumps.

So how does it work?

Liquids are a big challenge for 3D printers. Most approaches to printing with liquids require a post-printing step to clean up the messy surface of the resulting printed object. That step makes it hard for liquid-based methods to scale.

With "printable hydraulics," an inkjet printer deposits individual droplets of material that are each 20 to 30 microns in diameter, or less than half the width of a human hair. Using high-intensity UV light, the printer solidifies the substrate materials.

"Inkjet printing lets us have eight different print-heads deposit different materials adjacent to one another all at the same time," postdoc Robert MacCurdy, one of the paper's authors, explains. "It gives us very fine control of material placement, which is what allows us to print complex, pre-filled fluidic channels."

The hexapod robot printed using the printable hydraulics method moves with help from a single DC motor that pumps fluid to the robot's legs. Aside from its motor and power supply, every component is printed in a single step with no assembly required.

"If you have a crawling robot that you want to have step over something larger, you can tweak the design in a matter of minutes [with printable hydraulics]," MacCurdy says. "In the future, the system will hardly need any human input at all; you can just press a few buttons, and it will automatically make the changes."

There are still drawbacks. The hexapod took 22 hours to print, which is far too long if the technology is going to scale in a manufacturing environment. But it's still early going.

"Accelerating the process depends less on the particulars of our technique and more on the engineering and resolution of the printers themselves," says advisor Rus. "Printing ultimately takes as long as the printer takes, so as printers improve, so will the manufacturing capabilities."

The team's work was funded, in part, by a grant from the National Science Foundation.

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