Developed by engineers at MIT, Columbia, Cornell and Harvard, the particle robots are palm-sized discs with a series of magnetic connectors around their edges. Each of these ‘particles’ can both expand and contract, affecting the surrounding particles connected via their own magnets. This coordinated movement allows a cluster of the robots to travel in a particular direction, with onboard sensors guiding the swarm towards a light source.
Despite working in apparent harmony, none of the particles directly communicate with or rely on one another to function, so particles can be added or subtracted without any impact on the group. In a paper published in the journal Nature, the researchers described how particle robot systems could even complete tasks when several individual units malfunctioned.
“We have small robot cells that are not so capable as individuals but can accomplish a lot as a group," says Daniela Rus, director of MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL).
"The robot by itself is static, but when it connects with other robot particles, all of a sudden the robot collective can explore the world and control more complex actions. With these 'universal cells,' the robot particles can achieve different shapes, global transformation, global motion, global behaviour, and, as we have shown in our experiments, follow gradients of light. This is very powerful."
Each particle robot has a cylindrical base that houses a battery, a small motor, sensors that detect light intensity, a micro-controller, and a communication component. Mounted on top is a children's toy called a Hoberman Flight Ring - invented by one of the paper's co-authors - which consists of small panels connected in a circular formation that can be pulled to expand and pushed back to contract. Two small magnets are installed in each panel.
Particles that sense the most intense light move first in each wave of coordinated movement, with every particle broadcasting its light level to the rest of the swarm and onboard algorithms working out the sequence of action.
"This creates a mechanical expansion-contraction wave, a coordinated pushing and dragging motion, that moves a big cluster toward or away from environmental stimuli," said first author Shuguang Li, a CSAIL postdoc. According to Li, precise timing from a shared synchronized clock enables the cluster of particles to move as efficiently as possible: "If you mess up the synchronized clock, the system will work less efficiently,” he said.
In the lab, the researchers demonstrated a physical particle robotic system moving and changing directions toward different light bulbs as they're flicked on and working its way through a gap between obstacles. The team was also able to show that simulated clusters of up to 10,000 particles maintain locomotion even with up to 20 per cent of units failed.
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