Is there a connection between cheetahs and hairpins – the fastest butterfly robot comes out

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Actual picture of butterfly soft robot and swimming style (Photo courtesy of interviewee)

Everything is inspired, whether it’s a swift cheetah or a small hairpin – and it’s these two things that are incompatible that inspire the same research team.

The research process was beautiful, but the submission was not smooth. Although the research results were rejected by the top publications, Chi Yinding did not feel annoyed and anxious, but sighed: “I enjoy the research and submission process. Finally, the research paper, published Nov. 18 in Science Advances, introduced a soft robot that can swim butterfly and was featured in Nature Highlights.

“Compared with the current similar soft robots that can swim about 1 body length per second, the soft robot we developed can swim 3.74 body lengths per second, which is close to the relative swimming speed of dolphins, and the swimming process is very labor-saving.”

At the time of preparing this paper, Chi Yinding was a doctoral student of Yin Jie, an associate professor in the Department of Mechanical Aeronautics at North Carolina State University, and Yin Jie was also the corresponding author of the paper. Today, Chi Yinding is doing a postdoctoral fellow at the University of Pennsylvania, continuing his favorite soft robot research.

In Chi Yinding’s view, the significance of the research itself is far more important than the publication of the top journal. His supervisor Yin Jie agreed, telling China Science News: “We received a lot of valuable opinions during the submission process, which is conducive to us to further improve the existing research.” ”

Inspiration from girls’ hair cards

“We want to develop a soft robot like a manta ray, which not only swims faster, but also saves energy and effort.”

Yin Jie’s team has designed two kinds of butterfly swimming robots: one focuses on speed, the average swimming speed can reach 3.74 body lengths per second; the other focuses on flexibility, can turn quickly to the right or left, and the average swimming speed can reach 1.7 body lengths per second.

“When animals are swimming or flying, the Strauhar number (a dimensionless constant that evaluates energy efficiency) is between 0.2~0.4, and the best propulsion efficiency occurs.” Chi Yinding introduced, “The Strauhar number of the two butterfly swimming robots we designed is in this range. ”

Why is it called a butterfly soft body robot? The secret weapon is in the wings.

“The design of the wings of the butterfly soft robot is inspired by the snap hair cards commonly used by girls.” Chi Yinding pointed out that after pressing the two paddles of the issuing card and making a clicking sound, the issuing card can jump to another stable state, and the wings of the soft robot can also achieve such a “bistable state”.

“We attach the bistable wings that simulate hairpins to the soft silicone body, and by filling the fuselage with gas, we can control the wings to switch between the two steady states.” Chi Yinding describes, “When the silicone body expands and contracts, the soft robot’s body also bends, causing the wings to flexibly swing, as if a butterfly swimmer is swimming forward after slapping back and forth on the surface. ”

“Most of the soft robots developed in the past use electric motors to directly power the wings.” “We simplified the design and reduced the weight, ensuring that it can swim fast while saving effort. ”

In addition, Yin Jie’s team also uses two drive units connected side-by-side in the design of the butterfly soft robot, which can control the wings on both sides, and when the wing on one side is controlled to jump, the fuselage can make sharp turns.

The previous one was inspired by cheetahs

About two years ago, Yin Jie’s team had developed a soft robot that could not only run off the ground like a cheetah, but also easily grasp objects, and have enough force to lift heavy objects.

The soft robot design is inspired by the fastest running animal on land, the cheetah.

“Cheetahs can gain speed and strength by bending their spine.” Yin Jie said, “We were inspired by this, and the soft robot developed can quickly switch between two stable states by pumping air into the body of the soft silicone robot, allowing it to quickly store and release energy within tens of milliseconds, so as to quickly apply force to the ground to achieve running and jumping.” ”

Yin Jie’s team named the soft robot LEAP soft robot. Yin Jie introduced that compared with the fastest software robot reported at the time, which could move on a flat surface at a speed of 0.8 times the body length per second, the LEAP robot could achieve rapid “running” at a low driving frequency of 3Hz at a speed of 2.7 times the body length per second.

In the study, Yin Jie’s team also increased the swimming speed of the LEAP robot through the design of “fins”, allowing it to swim at a speed of 0.78 body lengths per second. The fastest speed of the swimming soft robot reported at the time was 0.7 body length per second.

In the previous paper, Chi Yinding is the second author. After that, he began to think about whether he could build on the original design to make the soft robot faster and more efficient.

From cheetah to hair card, it seems unrelated, but Chiyinding found a very important relationship between the two – bistability. Based on this, he made further improvements to the design, which not only significantly increased the swimming speed of the soft robot, but also made it more efficient and labor-saving.

However, Yin also pointed out the common flaws of the two studies: “Our soft robots need to be tethered by elongated tubes that pump air into the body. In the future, we hope to develop an autonomous robot without traction and untethered. ”

Missed out on the top publication’s Nature’s highlights

The submission experience of this paper can be described as a series of twists and turns.

“At the beginning, we chose Science Robotics, the top journal in the field of robotics, and entered the submission stage. Although reviewers found the study interesting and acknowledged that the design was very innovative, they were rejected. “We chose to vote for Nature, and the reviewers felt that our driver design could be improved. But the good news is that the editor-in-chief of Nature is very acknowledging our research and saying that the highlight can be given after publication. ”

Although he missed the opportunity to publish the top journals in the field, Chi Yinding was not very annoyed. He told China Science News: “The submission process allowed me to get more valuable suggestions that could help us better improve the design.” ”

Putting a good idea into practice can be challenging. The difficulties encountered in the research process also made Chi Yinding very interesting: “The issuing card definitely cannot swim, but the issuing card provides a bistable structure, and the issuing card is very light. Inspired by this, we designed the drive and structure of the soft robot, tried different drive modes, skeleton structures and plastic materials, and finally developed a soft robot that can not only swim butterflies, but also weighs very lightly, only 2.8g. ”

“From design to submission, it’s a process of continuous learning and improvement, so I enjoy it.” Chi Yinding hopes that he can continue to cultivate in this field.

Speaking of applications, Yin Jie revealed that the butterfly soft robot can overcome resistance to flexibly shuttle through the water, which is expected to be used for oil pollution cleaning and eutrophication treatment on the sea surface, and become a small helper for environmental protection. (Source: Shen Chunlei, China Science News)

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