Millimetre-scale walking robot is smallest ever

At 0.5mm wide, the robot can bend, twist, crawl, walk, turn and jump. The researchers also developed millimetre-sized robots resembling inchworms, crickets and beetles. The research is currently exploratory, but the team in Illinois, USA, believe their technology might bring the field closer to realising micro-sized robots that can perform practical tasks inside tightly confined spaces.

The research will be published on May 25, 2022, in Science Robotics.

In a statement, project leader John A. Rogers said: “Robotics is an exciting field of research, and the development of microscale robots is a fun topic for academic exploration. 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.”

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

The researchers said the robot crab derives its power from the elastic resilience of its body. To construct the robot, the researchers used a thermally actuated shape-memory alloy and used a scanned laser beam to rapidly heat the robot at different targeted locations across its body. A thin coating of glass elastically returns that corresponding part of structure to its deformed shape upon cooling.

As the robot changes from one phase to another it creates locomotion. Not only does the laser remotely control the robot to activate it, the laser scanning direction also determines the robot’s walking direction.

“Because these structures are so tiny, the rate of cooling is very fast,” said Rogers. “In fact, reducing the sizes of these robots allows them to run faster.”

To manufacture the machine, Rogers and Huang turned to a pop-up assembly method.

First, the team fabricated precursors to the walking crab structures in flat, planar geometries. They then bonded these precursors onto a slightly stretched rubber substrate. When the stretched substrate is relaxed, a controlled buckling process occurs that causes the crab to ‘pop up’ into precisely defined three-dimensional forms.

With this manufacturing method, the Northwestern team could develop robots of various shapes and sizes.

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