Researchers from Cornell University and the Max Planck Institute for Intelligent Systems have developed a swarm of tiny spinning robots that can work together to move objects. The microrobots use fluid forces to turn gears and push items without touching them.
The team published their findings on February 25 in Science Advances. Steven Ceron, Ph.D. ’22, now an assistant professor at the University of Michigan, is the lead author of the paper.
At very small scales, touching objects to move them becomes difficult. Flowing liquids offer a better way to handle delicate materials. The researchers wanted to see if many tiny robots working together could create enough force to do useful tasks.
Kirstin Petersen, associate professor at Cornell and co-senior author of the paper, explained the value of this approach. “At small scales, contact-based manipulation can be limiting, and flow-based manipulation offers a great alternative,” she said. Adding more robots creates stronger flows and greater force transfer.
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The robots are simple 3D-printed polymer discs about 300 micrometers in size. They are too small to carry computers or sensors. Instead, the researchers coated them with a thin magnetic layer. When placed in a small pool of water and exposed to changing magnetic fields, each disc spins on its axis.
As the discs spin, they create fluid flows around them. These flows change how the robots interact with each other and with objects in the water. The whole group starts to show behaviors that no single robot could produce on its own.
The team ran experiments with groups ranging from 10 to 1,000 robots. Together, they generated enough force to rotate multiple rings, turn circular gears, operate grippers, and move rack-and-pinion systems. They could also absorb and push dozens of passive objects floating in the water.
The researchers combined experiments with computer simulations to understand how the flows and interactions produced these behaviors. The results mostly matched expectations, but they also found something surprising.
When placed near a larger rotating object, the robots clumped together on one side and started crawling around its edge. This behavior emerged from how their flows interacted with each other and with the object’s boundary. Petersen said this crawling state could become useful for controlled transport or positioning at small scales in the future.
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The technology shows promise for biomedical applications that require gentle handling without direct contact. Instead of building complex machines, a swarm of simple robots could drive millimeter-scale elements like gears or grippers.
The research received support from the Max Planck Society, the National Science Foundation, the Fulbright Germany Scholarship, and the Packard Foundation Fellowship.
