Meet the world’s smallest remote-controlled walking robot: a minuscule crab

A team of researchers from Northwestern University, US, has created a tiny robotic crab that can stand on the edge of a coin.

The millimetre-scale crab – the smallest remote-controlled walking robot ever created – can walk, crawl, turn, jump, bend and twist. This flexibility of movement is supported by some innovative engineering.

The robot, described in a paper published today in Science Robotics, is constructed from a shape-memory alloy. When heated, this material returns to a specific “remembered” shape. A thin coating of glass coaxes the material into a different shape as it cools.

A video showing the robotic crab walking sideways. Credit: Northwestern University.

By using a laser beam to heat the robot at specific locations, the alternation between the “remembered” and “deformed” shapes causes the crab to move. The direction of the laser scanning controls the direction in which the robot walks.

“Because these structures are so tiny, the rate of cooling is very fast,” explains co-author John A. Rogers, who led the experimental work for the paper. “In fact, reducing the sizes of these robots allows them to run faster.”

Photograph showing a tiny robotic crab standing on the edge of a coin
The tiny robotic crab is small enough to stand on the edge of a coin. Credit: Northwestern University.

“Our technology enables a variety of controlled motion modalities and can walk with an average speed of half its body length per second,” adds Yonggang Huang, who led the theoretical work. “This is very challenging to achieve at such small scales for terrestrial robots.”

The robot is manufactured using a process inspired by children’s pop-up books. Flat precursors for the robot parts are bonded to a slightly stretched piece of rubber, causing them to “pop up” into three-dimensional shapes as the rubber relaxes. It’s a highly flexible manufacturing method.

Video showing the pop-up assembly mechanism. Credit: Northwestern University.

“With these assembly techniques and materials concepts, we can build walking robots with almost any sizes or 3D shapes,” says Rogers. “But the students felt inspired and amused by the sideways crawling motions of tiny crabs. It was a creative whim.”

The potential applications for such robots, however, go far beyond the merely whimsical.

“You might imagine micro-robots as agents to repair or assemble small structures or machines in industry, or as surgical assistants to clear clogged arteries, to stop internal bleeding or to eliminate cancerous tumours — all in minimally invasive procedures,” Rogers says.

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