Engineers at Northwestern University in Illinois have developed the smallest-ever remote-controlled walking robot – a tiny crab-shaped device, smaller than a flea, that can bend, twist, crawl, walk, turn and even jump.
‘Robotics is an exciting field of research, and the development of micro-scale robots is a fun topic for academic exploration,’ said John A Rogers, the Louis Simpson and Kimberly Querrey professor of materials science and engineering, biomedical engineering and neurological surgery at Northwestern’s McCormick School of Engineering and Feinberg School of Medicine,who led the experimental work.
‘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, the Jan and Marcia Achenbach professor of mechanical engineering and civil and environmental engineering at McCormick, who led the theoretical work. ‘This is very challenging to achieve at such small scales for terrestrial robots.’
Just a half-millimetre wide, the tiny crab isn’t powered by complex hardware, hydraulics or electricity. Instead, its power lies within the elastic resilience of its body.
To construct the robot, the researchers used a shape-memory alloy material that transforms to its ‘remembered’ shape when heated. In this case, the researchers 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 the structure to its deformed shape upon cooling.
As the robot changes from one phase to another – deformed to remembered shape and back again – it creates locomotion. The laser remotely activates the robot and its scanning direction determines the robot’s walking direction. Scanning from left to right, for example, causes the robot to move from right to left.
‘Because these structures are so tiny, the rate of cooling is very fast,’ Rogers explained. ‘In fact, reducing the size of these robots allows them to run faster.’
In order to manufacture such a small robot, Rogers and Huang turned to a technique that they introduced eight years ago – a pop-up assembly method that was inspired by a pop-up book for children. First, they 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 these assembly techniques and materials concepts, we can build walking robots with almost any sizes or 3D shapes,’ Rogers said. ‘But the students felt inspired and amused by the sideways crawling motions of tiny crabs. It was a creative whim.’
The researchers also developed millimetre-sized robots that resemble inchworms, crickets and beetles. Although the research is exploratory at this point, the researchers believe that their technology might bring the field closer to realising micro-sized robots that can perform practical tasks inside tightly confined spaces.
‘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 said.
Last September, the same team introduced a winged microchip that was the smallest-ever human-made flying structure.
The research has been published in Science Robotics.