In Its Own Image: Simple robot replicates itself block by block

Peter Weiss

No robot can reproduce the way that algal cells, begonias, and people can. However, an automaton that's little more than a stack of blocks has shown that it, too, can make more of its own kind.

JUST LIKE ME. In frames from a video (bottom), a stack of modules of the type shown in the top image builds a duplicate stack. The dots on some of the modules' faces are magnets and electrical contacts. V. Zykov et al./Nature

Self-replicating robots could be a boon for space exploration and for jobs such as clearing minefields, says Hod Lipson of Cornell University, who led the new research. Ideally, he says, self-copying robots would build coworkers from materials on hand and also repair themselves.

The researchers describe their robotic-block constructions, composed of modules they call "molecubes," in the May 12 Nature. Harboring a microprocessor, a motor, and electromagnets, each fist-size cube consists of plastic halves that swivel along a diagonal plane. As an assemblage of cubes copies itself, the modules execute a sequence of rotations programmed into their microprocessors. At the same time, the modules use their electromagnets to release cubes or pick up others that researchers place within the robot's reach.

The parent assumes a variety of shapes, such as L's and upside-down U's, as it twists and bends to build a copy of its original shape. Lipson says that his team plans to develop millimeter-to-micrometer-size modules.

Jordan B. Pollack of Brandeis University in Waltham, Mass., says the Cornell work "is a tour de force of elegant engineering ... and a precursor to some tremendously flexible microrobotic machinery of the future."

Scientists and engineers have pursued self-replicating constructions since the 1940s, when theoreticians began working out concepts of mechanical replication, notes Moshe Sipper of Ben-Gurion University in Beer Sheva, Israel. A few researchers have made mechanical gadgets of materials such as wood or plastic blocks that made copies of themselves using components in their surroundings.

The new molecubes may be better suited to self-replicating complex devices, says Mark Yim of the University of Pennsylvania in Philadelphia. Lipson notes that his group has already simulated on a computer an F-shaped self-replicating robot made of the blocks, but not yet built it.

Ultimately, more-complex structures may be possible. Think of a car made of many identical modules, adds Sipper. "It hits a wall maybe, but it's able to self-repair."

Not all scientists developing self-replicating machines are impressed with the Cornell research. Gregory S. Chirikjian of Johns Hopkins University in Baltimore faults the work for assembling complex starting materials in a trivial manner, rather than the other way around. More impressive, he says, would be a robot that starts with simpler parts and assembles them into a more-complex result.

Although Sipper also points out such limitations of the molecube approach, he says that it "opens up nice avenues."

Letters:

This article makes the common claim that self-replicating robots could be a boon for clearing minefields. In truth, a complex electronic device simply does not last long in the field. When it breaks and you are 3 days from the nearest town, where do you get a spare part or battery? Tools for removing land mines need to be affordable, simple to manufacture and repair in a mined area, and 100 percent accurate under highly variable conditions. What robot meets these criteria?

Andrew Heafitz
Massachusetts Institute of Technology
Cambridge, Mass.

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References:

Zykov, V. . . . and H. Lipson. 2005. Robotics: Self-reproducing machines. Nature 435(May 12):163-164. Abstract available at http://dx.doi.org/10.1038/435163a.

Further Readings:

Lipkin, R. 1994. Simulated creatures evolve and learn. Science News 146(July 23):63.

Weiss, P. 2000. Robots making robots, with some help. Science News 158(Sept. 16):189. Available to subscribers at http://www.sciencenews.org/articles/20000916/note15.asp.

A version of this article written for younger readers is available at Science News for Kids.

Sources:

Gregory S. Chirikjian
Department of Mechanical Engineering
Johns Hopkins University
Baltimore, MD 21218

Hod Lipson
Department of Mechanical and Aerospace Engineering
Computing and Information Science
Cornell University
Ithaca, NY 14853

Jordan B. Pollack
Department of Computer Science
Volen Center for Complex Systems
Brandeis University
Waltham, MA 02254

Moshe Sipper
Department of Computer Science
Ben-Gurion University
P.O. Box 653
Beer-Sheva 84105
Israel

Mark Yim
GRASP Laboratory
3330 Walnut Street
Levine Hall, 4th Floor
Philadelphia, PA 19104