Scientific Method / Science & Exploration

Flexible robots, in (not quite) living color

If you model your robot on a cephalopod, it should change colors, right?

S. Morin, Harvard

Last year, we covered a radically different approach to robotics. Instead of the hard, mechanical skeletons that are features of most robots, a team was inspired by squid, and built a soft, flexible robot that ran on air. By pumping different segments of their robot full of air using a set of pre-programmed commands, the rubbery creation could flex its legs and stride across surfaces, slipping neatly under barriers when needed.

But if the researchers were inspired by cephalopods like the octopus and cuttlefish, then they seemed to also have been a bit jealous of one of these creatures' other abilities: rapidly changing color to match their surroundings or make a warning display. So the team is back with a modified version of their previous robot—one that can change color on demand.

The method for doing this was a straightforward variation on the technique used to propel the robot: an external compressor was used to pump material into the robot from an external reservoir. Instead of air, however, the material was a fluid that contained a variety of dyes or fluorescent molecules that gave the robot some color.

The fluid went into a separate set of channels from those that propelled the robot, giving the team a great deal of flexibility. This allowed them to create patterns like the stripes shown above, which are probably closer to a zebra's than anything that would typically show up on a cephalopod. But the team also crafted some patterns that were more like a mottled patchwork, which could be more useful for camouflage (as they demonstrated on a backdrop consisting of small rocks).

Although their robot is shaped like a squashed X, it can easily move while carrying an irregular sheet of tubes on top. This let the authors build more elaborate camouflage patterns, such as the one shown below. The whole process is reversible, too, so the robot could be restored to its translucent, colorless form, or have one set of colors replace another.

Enlarge / The robot above, covered with a flexible plastic cover, filled with a patchwork of fluorescent dyes.
S. Morin, Harvard

Although these images use some pretty garish dyes, the system can use pretty much anything that will work in liquid form. It would even work with gasses. For different environments (rocks, leaves, patterned flooring), the robots were fed liquids with appropriate colors. The authors also tested fluorescent dyes, as well as materials that absorbed or reflected infrared light. All of it worked about as well as you'd expect, given that there was nothing more elaborate involved than pumping liquid through a series of tubes.

There are a few obvious limitations to this approach, but they're pretty big ones. The system can only work with whatever dyes it has prepared in advance, so it can't do the huge range of arbitrary colors that many animals can generate (Although it could be possible to blend a set of dyes and get a pretty broad range). And, although a potentially infinite set of patterns of dye tubes could be crafted, any robot is stuck with whatever it was made with—you cant just go from a patchwork to stripes when desired.

It's also very slow. Fluid can only move through the tubes at a set speed, and many of them wind across the surface of the robot. Completely filling out a pattern can take dozens of seconds.

All of these limitations mean that this is mostly a proof-of-principle, albeit one with a very high coolness factor. The authors suggest that it could provide a useful tool for others—they specifically mention people who study animal camouflage as one group who might find uses for it, as well as seeing some potential in medical simulators.

Still, it's hard to get too cynical about the robot's future prospects. With two major publications in under a year, it's clear the people behind it are busy thinking up new things to do with their platform.

Science, 2012. DOI: 10.1126/science.1222149  (About DOIs).

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