Both of these issues are a major drawback for disaster relief applications, which small devices are otherwise well-suited to thanks to their ability to squeeze into confined spaces.
Researchers at the Massachusetts Institute of Technology (MIT) have targeted the best of both locomotion methods with a new hopping and flapping robot, which can leap over tall obstacles and jump across uneven surfaces while reportedly using far less energy than a conventional flying device.
The hopping robot, which is smaller than a human thumb and weighs less than a paperclip, has a springy leg that propels it off the ground, and four flapping wings that give it lift and control its orientation. It can jump about 20cm into the air, four-times its height, at a lateral speed of about 30cm per second, while consuming about 60% less energy than equivalent flying devices.
Due to its low weight and durability, and the energy efficiency of the hopping process, researchers said the robot could carry about 10-times more payload than a similar-sized aerial robot, opening the door to many new applications.
“Being able to put batteries, circuits, and sensors onboard has become much more feasible with a hopping robot than a flying one. Our hope is that one day this robot could go out of the lab and be useful in real-world scenarios,” said Yi-Hsuan (Nemo) Hsiao, an MIT graduate student and co-lead author of a paper on the hopping robot.
The robot is fitted with an elastic leg made from a compression spring, similar to the spring on a click-top pen. This spring converts the robot’s downward velocity to upward velocity when it strikes the ground.
“If you have an ideal spring, your robot can just hop along without losing any energy. But since our spring is not quite ideal, we use the flapping modules to compensate for the small amount of energy it loses when it makes contact with the ground,” Hsiao said.
The flapping wings provide lift as the robot bounces back up into the air, while ensuring it remains upright and has the correct orientation for its next jump. The four flapping wing mechanisms are powered by soft actuators, or artificial muscles, that are durable enough to hit the ground repeatedly without being damaged.
“We have been using the same robot for this entire series of experiments, and we never needed to stop and fix it,” Hsiao said.
A fast control mechanism determines how the robot should be oriented for its next jump, while sensing is done by an external motion-tracking system. The team put the device and its controls to the test on a variety of surfaces, including grass, ice, wet glass and uneven soil. The robot managed to cross all of the obstacles, and could even hop on shifting surfaces.
The researchers showcased its agility by demonstrating acrobatic flips. The featherweight robot could also hop onto an airborne drone without damaging either device, which they said could be useful in collaborative tasks. The team hopes to make the robot autonomous by installing batteries, sensors and other circuits.
“Multimodal robots (those combining multiple movement strategies) are generally challenging and particularly impressive at such a tiny scale. The versatility of this tiny multimodal robot – flipping, jumping on rough or moving terrain, and even another robot – makes it even more impressive,” said Justin Yim, assistant professor at the University of Illinois at Urbana-Champagne, who was not involved in the work.
“Continuous hopping shown in this research enables agile and efficient locomotion in environments with many large obstacles.”
This research was partly funded by the US National Science Foundation and the MIT Misti programme. The work appeared in Science Advances.
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