Robots have helped us explore the world, from the ocean’s depths to mountain peaks, and even into outer space. But while researchers have made robots that can swim, run and fly better than their biological counterparts, engineers have struggled to build a bot that can burrow as well as an animal.
To design a device that could navigate the subterranean world, researchers at the University of California and the Georgia Institute of Technology decided to take inspiration from nature.
Instead of using a mechanical drill to overcome the resistant forces in the ground, the team have built a flexible soft robot that works with physics, instead of against it.
The soft robot moves through a sandy terrain in several ways. To travel straight down, the robot acts like a plant’s root system, with a tip that extends to push surrounding material out of its way. The team can control the movements of the bot using 'tendons' on either side, and steering with these enable the robot to make sharp turns along tortuous paths.
To move horizontally through the ground, the robot imitates the burrowing sand octopus: blowing air from its tip in asymmetrical directions to overcome the resistance of the sand and get from A to B. This is referred to as air fluidisation, as it keeps the solid particles of sand moving, much like the particles within a fluid.
"Unlike in a gas or liquid, a symmetric object moving horizontally through a granular media experiences lift. It is simply easier to push the sand up and out of the way than it is to compact it down," said Dr Nicholas Naclerio, lead author of the research.
"As a result, with only forward airflow, our robot resurfaces. This lift force is countered by adding a downward airflow to the robot. The asymmetric combination of both forward and downward airflow enables controllable horizontal burrowing."
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Though the robot developed by the team for this new research is just 6cm in diameter, with a tip able to extend to 1m, researchers say they have designed bots as small as 2mm and as large as 70m.
The combination of tip extension and air fluidisation technology was tested in a sandy environment, but the team are now working with NASA to develop a robot that can burrow on the surface of the Moon, or be sent to explore far away bodies such as Enceladus, a moon of Jupiter.
"Soft robots are unproven in space, but we believe they could be powered by a small tank of compressed gas, a chemical gas generator, or by collecting gas from the local environment," explained Naclerio.
"Air fluidisation only works in dry granular media, like sand. However, fluidising with water works in damp, or cohesive media, like dirt and clay.
"Tip extension could also be used with other mechanisms, such as drills, to explore other environments."
