Pleobot: the robot for ocean exploration inspired by krill


Inspenet, September 16, 2023.

Pleobot, a robot that takes inspiration from krill , proposes promising solutions for underwater mobility and ocean exploration, both on Earth and on the moons of our solar system. In a recent report published in Scientific Reports, a team led by scientists at Brown University has taken its first significant steps in creating these underwater navigation robots .

The study details the design of a small robotic platform called Pleobot that could serve as a tool to help researchers understand the krill-like swimming method and as a basis for building compact, highly maneuverable underwater robots .

This consists of three articulated segments that imitate the swimming of krill. Scientists took him as inspiration for his ability in swimming, acceleration, braking and maneuvering. The study illustrates its capabilities by emulating the movements of krill’s legs during swimming, shedding light on the complex interactions between the machine’s structure and the aquatic environment that allow constant swimming in the tiny marine species.

According to the research, it has the potential to provide the scientific community with valuable insight into how to harness 100 million years of evolution to design more efficient marine robots.

“Experiments with organisms are challenging and unpredictable,” says Sara Oliveira Santos, a doctoral candidate at the Brown School of Engineering and lead author of the new study. “Pleobot allows us unparalleled resolution and control to investigate all aspects of krill-like swimming that help it excel in underwater maneuvers. “Our goal was to design a comprehensive tool for understanding krill-like swimming, which meant including all the details that make krill such an athletic swimmer.”

This project is a collaboration between two groups of researchers: the team of Mónica Martínez Wilhelmus, assistant professor of engineering at Brown University, and the group of scientists led by Francisco Cuenca-Jiménez at the National Autonomous University of Mexico.

Krill: the source of inspiration

One of the main objectives of the project is to obtain a deep understanding of how swimmers using the metachronous technique manage to function effectively in highly complex marine environments and carry out large-scale vertical migrations, exceeding 1,000 meters in depth.

“We have snapshots of the mechanisms they use to swim efficiently, but we don’t have complete data,” says Nils Tack, a postdoctoral associate in the Wilhelmus laboratory. “We built and programmed a machine that precisely emulates the essential movements of the legs to produce specific movements and change the shape of the appendages. “This allows us to study different setups to take measurements and make comparisons that would otherwise be impossible to obtain with live animals.”

The metachronous swimming technique, which involves the sequential and coordinated use of the limbs, can provide noticeable agility, a characteristic that krill frequently exhibit by moving their swimming legs in a back-and-forth wave pattern. Scientists anticipate that in the future, deployable swarm systems could find applications in mapping Earth’s oceans, participate in search and recovery missions spanning vast areas, or even be sent to moons within the solar system, such as Europa, with the purpose of exploring the oceans of these moons.

“This study is the starting point of our long-term research goal of developing the next generation of autonomous underwater detection vehicles. Being able to understand fluid-structure interactions at the appendage level will allow us to make informed decisions about future designs,” says Wilhelmus.

Likewise, scientists have active control over the two segments of Pleobot’s legs and passive control of its birame fins. This achievement is considered the first to faithfully replicate the opening and closing movement of these fins. The creation of this robotic platform involved a multi-year project involving an interdisciplinary team spanning fluid mechanics, biology and mechatronics.

The model the researchers built is ten times the scale of krill, which is typically the size of a paper clip. The platform is mainly made up of parts manufactured using 3D printing and its design is open source, allowing other teams to use it to further investigate metachronous swimming, not only in the context of the aforementioned marine species, but also in relationship with other organisms, such as lobsters.

In their research, the team reveals the solution to one of several puzzles related to krill swimming: how they generate the force necessary to avoid sinking while swimming forward. Since this is slightly heavier than water, if it doesn’t swim steadily it will start to sink. Therefore, even when they swim forward, they must generate some upward force to stay at the same depth in the water, explains Oliveira Santos.

“We were able to discover that mechanism using the robot,” says Yunxing Su, a postdoctoral associate in the lab. “We identified an important effect of a low-pressure region on the back of the swimming legs that contributes to improved lifting force during the moving leg power stroke.”

In the near future, scientists plan to build on this initial achievement, further refining and testing the designs that have been detailed in the report. Currently, they are working to incorporate morphological traits of the shrimp into the robotic platform, such as their flexibility and the bristles surrounding their appendages. Initial funding came from a NASA EPSCoR grant in Rhode Island.

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