Inspired by the way ants move through narrow spaces by shortening their legs, scientists have created a robot that retracts its limbs to navigate narrow passages.
The robot could bend over and quickly pass through passages that were narrower and shorter than itself, researchers reported on January 20 in Advanced Intelligent System s. It could also climb stairs and move over grass, loose rocks, mulch and crushed granite.
Such generality and adaptability are the main challenges of walking robots, says robotics engineer Feifei Qian, who was not involved in the research. Some robots have specialized limbs to move around a certain area, but they cannot squeeze into small spaces.
“Design that can adapt to a variety of environments with different scale or stiffness is much more difficult because you have to consider the trade-offs between the different environments,” says Qian of the University of Southern California in Los Angeles.
For inspiration, researchers in a new study turned to ants. “Insects are a really good inspiration for designing robotic systems that have minimal actuation but can perform a multitude of motor actions,” says Nick Grevish, a roboticist at the University of California, San Diego. Ants adapt their posture to crawl through tiny spaces. And they are not bothered by uneven terrain or small obstacles. For example, their legs bend slightly when they hit an object, Greivish says, and the ants continue to move forward quickly.
Gravish and his colleagues built a short stocky robot — about 30 centimeters wide and 20 centimeters long — with four wavy, telescoping limbs. Each limb consists of six nested concentric tubes that can be retracted into each other. Furthermore, the limbs do not need to be activated or adjusted to change their overall length. Instead, the springs that connect the leg segments automatically allow the legs to compress when the robot moves in a narrow space and extend back when the robot is in an open space. The goal was to build mechanically intelligent structures, not algorithmically intelligent robots.
“It’s probably faster than active steering, [що] requires the robot to first sense contact with the environment, calculate an appropriate action, and then send a command to its motors,” Qian says of those legs. Removing sensors and computing components can also make robots smaller, cheaper, and less energy-intensive.
The robot could vary the width and height of its body to achieve a greater range of body sizes than other similar robots. The leg segments retracted inward, allowing the work to move through small tunnels and stretch out under the low ceiling. With these adaptive capabilities, the robot squeezed into a space that was only 72 percent of its full width and 68 percent of its full length.
Like ants, the new type of robot can squeeze its legs to move in narrow spaces and hunch over to cross spaces shorter than itself. It can also climb stairs and move over grass and loose stones.
Next, the researchers plan to actively control the stiffness of the springs that connect the leg segments to adjust the movement according to the type of terrain without consuming too much energy. “That way you can keep your leg long when you’re moving across open terrain or over tall objects, but then collapse into the smallest possible shape in a confined space,” Grevish says.
Such small, minimal robots are easy to manufacture and can be quickly configured to explore complex environments. However, despite their ability to walk across different terrains, these robots are currently too fragile for search and rescue, reconnaissance or biological monitoring, says Greivish.
The new robot takes a step closer to those goals, but achieving that goal will require more than just robotics, Qian says. “Achieving these applications will require the integration of design, control, sensing, planning and hardware improvement.”
But this does not interest Grayvish. Instead, he wants to connect these experiments to what was first observed in ants, and use the robots to ask more questions about the rules of locomotion in nature.
“I would really like to understand how small insects can move so quickly over some unpredictable terrain,” he says. “What is so special about their limbs that allows them to move so fast?”
