This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
When you imagine a robot, you might picture R2-D2 in Star Wars, the Omnidroid from The Incredibles or the big-armed machines that build cars on an assembly line. But there’s a new robotic system that doesn’t resemble any of these. Instead, it looks like some kids forgot to pick up their toys.
The robot is a collection of plastic, neon-green disks. Each is about 15 centimeters (6 inches) across. Alone, a single disk can’t do much of anything. It can only expand and contract.
But when a bunch of disks huddle together, things change. Tiny magnets on the disks’ outer rims make them stick together. When one disk expands or shrinks, it pushes or pulls on its neighbors. All of those small pushes and pulls add up. Suddenly the entire blob starts to move — very slowly.
The designers refer to each individual disk is a “particle.” When working as a system, they become what the designers call a “particle robot.” The researchers shared their invention March 20 in Nature. In the new study, they also showed how such a particle robot can accomplish simple tasks, like shuffling toward a light.
“It’s an innovative mechanism,” says Katia Sycara. She’s a computer scientist at Carnegie Mellon University in Pittsburgh, Pa., who designs multi-robot systems. She did not work on the new invention. But she says it illustrates the wild variety of ways that people can build robotic systems.
At one end of the spectrum of robots you find single-bodied devices. Think R2-D2. These are robots contained in just one body. At the other end of the spectrum are modular robots. These are groups of individual robots that each have their own job but together work on some common task. They include “swarm” robots, which talk to each other and share information about where and how they’re moving.
The new system, says Sycara, is somewhere in between. The disks are individual units, but they bunch together to form a unified team. Their behavior results from their interactions and the laws of physics, not someone telling them what to do.
“We wanted to make robots that are very simple and that can respond to changes in the environment,” says Richa Batra. She’s a graduate student at Columbia University in New York City and part of a multi-university team behind the new particle-robotics system.
Scientists behind the project were inspired by nature, Batra explains. In the human body, for example, individual cells work together as muscle tissue. Many other types of cells also move together as a group.
The motion of the robot also reminds Batra of something else in the living world. The blob shuffles along “like a caterpillar moves,” she says. “It bunches up a little, then stretches out.”
Even though the disks don’t communicate directly with each other, they can respond as a group to some signal. The scientists showed this by installing sensors on each disk that could detect light. Then they programmed the disks to expand and contract faster or slower, depending on how intense the light was. When the researchers shone a bright light, their robot crept toward it — the result of all those individual expansions and contractions.
To make sure the group of particles would not get stuck, the researchers had to consider how friction would affect the disks. Friction is the resistance between two surfaces rubbing together. The disks had to push hard enough to overcome friction. But they couldn’t push each other so far away that their magnets stopped working.
Another challenge the researchers faced was deciding what the disks should look like. For help, they turned to Chuck Hoberman at Harvard University in Cambridge, Mass. He had created what are known as Hoberman Spheres. The clever plastic toys are made of interconnected arms that expand into giant spheres when thrown in the air, and then collapse back into small spheres when caught. The new robotics team recruited Hoberman to design the disks that would become their “particles.” Like his spheres, these, too, get bigger and smaller with minimal effort.
Finally, the scientists had to create a system that could work at different scales. So far, they have built physical robots with more than two dozen disks. But they wanted to show what would happen with groups of hundreds, or even thousands, of particles. That’s where Batra came in. For two years, she wrote computer programs that could predict the behavior of big groups. She showed how a system with 100,000 particles would move. Her software also predicted what would happen if individual disks in the group stopped working.
“That was one of the really beautiful things we were able to look at,” she says. “How many of these particles could be killed off and still have it move?” A lot, as it turns out. Batra ran calculations on robots made from hundreds — even thousands — of particles. Her program predicted that even if one in five disks malfunctioned and stopped moving, the system would still be able to move as a group.
Right now, the robot only moves across a flat surface. Batra says she wants to know what a three-dimensional system might look like. The researchers also don’t know yet how their flat system might be used.
Still, that’s normal for robotics, says Sycara. Each new approach adds to the toolbox that other researchers can later use.
Sycara predicts that future robots, such as this one, will continue to take cues from nature on how they might look and move. “We are going to be seeing more and more biologically inspired designs,” she says.
behavior The way something, often a person or other organism, acts towards others, or conducts itself.
caterpillar The larval stage of moths and butterflies. Somewhat wormy-shaped crawlers, caterpillars tend to eat leaves and other plant bits. Some will, however, dine on other insects.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
computer program A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.
contract To activate muscle by allowing filaments in the muscle cells to connect. The muscle becomes more rigid as a result.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).
friction The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage a surface of some material as it rubs against another.
graduate student Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).
magnet A material that usually contains iron and whose atoms are arranged so they attract certain metals.
mechanism The steps or process by which something happens or “works.” It may be the spring that pops something from one hole into another. It could be the squeezing of the heart muscle that pumps blood throughout the body. It could be the friction (with the road and air) that slows down the speed of a coasting car. Researchers often look for the mechanism behind actions and reactions to understand how something functions.
muscle A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.
particle A minute amount of something.
physical (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
resistance (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.
robot A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.
sensor A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.
software The mathematical instructions that direct a computer’s hardware, including its processor, to perform certain operations.
spectrum (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.
swarm A large number of animals that have amassed and now move together. People sometimes use the term to refer to huge numbers of honeybees leaving a hive.
tissue Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.