Physicist Heinrich Jaeger turns his granular-materials experience to robotics.

By Benjamin Recchie, AB’03
Photographyby Beth Rooney; Jambot images courtesy Jaeger Group

A newcomer to robotics, Jaeger built a device with properties of both solids and liquids.

The very word “robot” brings to mind metal, wires, and the whir of motors. You might picture the mechanical arms that assemble cars, the Predator aerial drone, the comical droids of Star Wars—or the sinister ones of Terminator. Physics professor Heinrich Jaeger imagines a different concept: the robot as self-propelled beanbag.

Since Jaeger, a condensed-matter physicist, arrived at the University in 1991, he’s become best known for his work exploring the unusual properties of granular materials: although each individual grain is a solid, large agglomerations of them take on the characteristics of fluids. Jaeger has found that this phenomenon holds true for many different kinds of “grains,” from sand in an hourglass to cars on a freeway.

In 2007 Jaeger’s research led to an unexpected undertaking, when a request for proposals from the Defense Advanced Research Projects Agency (DARPA) thrust him into the unfamiliar world of robotics. The U.S. military agency tasked with fostering emerging technologies, DARPA had long been interested in self-propelled robots. (Its list of previous projects includes the aforementioned Predator drone and a self-driving Humvee.) However, such robots have their limitations—wheels, batteries, arms, and motors make them too unwieldy to, for example, squeeze through small holes. “It would be very advantageous,” Jaeger explains, “if you had a robot that could act in some disaster where debris has blocked ordinary entrances or exits—to send something through the rubble that can change its shape in ways that an ordinary robot couldn’t.” The agency wanted a robot that could, among other things, change its diameter by a factor of ten and scoot through a hole less than one inch in diameter. This requirement meant that the robot must be able to alternately change or hold its shape—a perfect application of Jaeger’s research into the jamming of granular materials.

Jamming is a deceptively simple concept. Jaeger gives the example of a vacuum-packed coffee brick: when the brick is sealed, the pressure that the wrapper exerts holds the coffee grounds together like a solid block, but opening the package (and releasing the pressure) lets them flow out like a liquid. After years of working with colleagues, including postdoctoral scholar Eric Brown, on the fundamental physical principles underlying jamming, such as surface tension and cohesion, Jaeger says, he and his group had asked themselves, “Now that we know all of this, can we find an application for it?”

The request from DARPA was just the challenge they were looking for. Because Jaeger was an “outsider to the robotics community,” he says, he and his group rounded up other collaborators to help build what they dubbed the Jambot: a team from the University of North Carolina, Liquidia Technologies, and iRobot, the company best known for its Roomba vacuum cleaner.

Made up of a “secret” granular material encased in elastic membranes, Jaeger's robot can shrink or expand tenfold by turning the membranes rigid or soft.

First, the Jambot team had to find an appropriate jamming material. They settled on a sand-like blend of granular material, designed by UNC and produced by Liquidia. (Jaeger calls it “our secret mixture.”) They contained a few grams of the material in an elastic membrane that could shrink tight around it to make it rigid, or loosen to make it soft and flexible. The final Jambot consisted of several sections of such membrane-enclosed material; by alternately turning them rigid or soft, the robot could push itself across the floor and change its shape as necessary.

A prototype Jambot, which demonstrated only the basic functions of the jamming membrane, was completed in 2008; a finished product that met all of DARPA’s demands was presented to the agency earlier this year.

Yet even after Jaeger delivered the robot, which was the size of a 12-ounce soft-drink can, he wasn’t finished with robotics. He and Brown have designed a gripper using jamming and flexible structures that could replace a robotic claw. A typical claw needs hinges, motors, and feedback sensors to prevent it from crushing the object it’s trying to hold, and the computational power to operate them. But Jaeger’s jamming-based gripper is more like a beanbag, flowing around the object and then holding it gently. “We came at this from a completely different perspective,” he says, “looking for a way to short-circuit this inherent complexity.”

With the University’s Office of Technology and Intellectual Property, Jaeger and Brown are trying to commercialize their gripper. While a robotic hand strong enough to carry a bowling ball but gentle enough to pick up an egg has numerous potential applications, Jaeger has a particular one in mind: an arm that firefighters could use to move objects inside a burning building regardless of their temperature. “Maybe this could be just the ticket.”


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