If you're making a small robot that can explore tight spaces, it would be good if that device could also shimmy its way through narrow gaps. An experimental new robot can do just that, by emulating a caterpillar.
The 9-cm (3.5-in)-long soft-bodied robot is being developed at North Carolina State University, by a team led by Prof. Yong Zhu.
It's modeled after the caterpillar of the mother-of-pearl moth (Pleurotya ruralis). Like other caterpillars, that one moves forward or backward by sequentially curling up segments of its body – the body-curl moves either from front to back, or back to front. And while the caterpillar uses its muscles to do so, the robot uses nanowire heaters.
Its body is made of two stacked layers of different polymers – the one on top expands when heated, while the one on the bottom contracts when heated. Embedded within the top layer is a network of silver nanowires, featuring multiple lead points along the length of the robot.
When an electrical current is applied at any one of those points, the nanowires in that area heat up, thus heating the polymer around them. This causes the robot's body to curl upwards in that area only. So, by sequentially applying a current to multiple adjacent lead points, it's possible to generate a curl that runs down the body in either direction.
"We demonstrated that the caterpillar-bot is capable of pulling itself forward and pushing itself backward," said postdoctoral researcher Shuang Wu, first author of the study. "In general, the more current we applied, the faster it would move in either direction. However, we found that there was an optimal cycle, which gave the polymer time to cool – effectively allowing the 'muscle' to relax before contracting again."
By selectively activating the nanowire heaters in the front and rear of the robot, the researchers were able to move it through a 30-mm (1.2-in)-long gap measuring just 3 mm in height. The robot can be seen doing so in the video below.
"This approach to driving motion in a soft robot is highly energy efficient, and we’re interested in exploring ways that we could make this process even more efficient," said Zhu. "Additional next steps include integrating this approach to soft robot locomotion with sensors or other technologies for use in various applications – such as search-and-rescue devices."
The research is described in a paper that was recently published in the journal Science Advances.
Source: North Carolina State University