Pleobot is a small robotic platform that emulates krill-like swimming.
Newswise — PROVIDENCE, R.I. [Brown University] —Imagine envisioning a network comprising interconnected, self-governing robots harmoniously engaging in a synchronized dance to explore the enigmatic depths of the pitch-black ocean, diligently carrying out vital scientific surveys or embarking on daring search-and-rescue missions.
In a groundbreaking research publication featured in Scientific Reports, a team of accomplished researchers from Brown University has unveiled a remarkable pioneering endeavor towards the realization of such underwater navigation robots. This study delineates the conceptualization of a diminutive robotic platform aptly named Pleobot, which serves as an invaluable tool for comprehending the locomotion technique akin to that of krill and lays the groundwork for constructing compact, highly agile underwater robots.
At present, Pleobot consists of three interconnected segments that faithfully emulate the metachronal swimming method observed in krill. The inspiration for Pleobot's design stems from the awe-inspiring athleticism of these aquatic creatures, who effortlessly navigate through water, deftly accelerating, decelerating, and executing intricate turns. The research study convincingly showcases Pleobot's capacity to mimic the leg-like movements of swimming krill, thereby shedding new light on the fluid-structure interactions indispensable for sustaining a smooth and uninterrupted forward motion in these marine organisms.
The study posits that Pleobot holds tremendous potential to empower the scientific community in discerning how to leverage 100 million years of evolutionary brilliance to engineer superior robots capable of oceanic navigation. With Pleobot as a vantage point, researchers can glean invaluable insights into harnessing the wonders of nature to fabricate robots that exhibit unrivaled maneuverability and efficiency while traversing the ocean's vast expanses.
"We face considerable challenges and uncertainties when conducting experiments involving organisms," explained Sara Oliveira Santos, the lead author of the new study and a Ph.D. candidate at Brown's School of Engineering. She added, "With Pleobot, we have achieved an unprecedented level of precision and control, enabling us to investigate all the intricate aspects of krill-like swimming that contribute to their exceptional underwater maneuverability. Our objective was to develop a comprehensive tool that would provide insights into the mechanics of krill-like swimming, encompassing all the intricate details that make these creatures such remarkable swimmers."
This endeavor is a collaborative effort between researchers from Brown University's Assistant Professor of Engineering Monica Martinez Wilhelmus' laboratory and scientists from Francisco Cuenca-Jimenez's laboratory at the Universidad Nacional Autónoma de México.
A significant goal of the project is to comprehend how metachronal swimmers, such as krill, successfully operate in intricate marine environments and accomplish massive vertical migrations exceeding 1,000 meters—equivalent to stacking three Empire State Buildings—twice daily.
"We currently possess partial insights into the mechanisms utilized by krill to achieve efficient swimming, but our data is not comprehensive," explained Nils Tack, a postdoctoral associate in the Wilhelmus lab. He continued, "To overcome this limitation, we constructed and programmed a robot that faithfully replicates the crucial movements of the krill's legs, enabling us to generate specific motions and modify the shape of the appendages. This setup allows us to investigate different configurations, acquire measurements, and draw comparisons that would otherwise be unattainable using live animals."
The metachronal swimming technique, characterized by the sequential activation of the swimming legs in a wave-like motion from back to front, grants krill impressive maneuverability. The researchers envision that in the future, deployable swarm systems could be utilized for ocean mapping on Earth, expansive search-and-recovery missions, or even exploration of the oceans on celestial bodies like Europa, a moon in the solar system.
"Krill aggregations serve as a remarkable example of natural swarms, consisting of streamlined organisms capable of traveling up to one kilometer in both directions, exhibiting exceptional underwater maneuvering abilities," stated Wilhelmus. "This study marks the initial phase of our long-term research objective to develop the next generation of autonomous underwater sensing vehicles. By comprehending fluid-structure interactions at the level of appendages, we will be equipped to make informed decisions regarding future designs."
The researchers possess active control over the two leg segments of the Pleobot and exhibit passive control over its biramous fins, marking a significant achievement as it emulates the fins' opening and closing motion for the first time. The construction of this robotic platform was a multi-year endeavor, involving a diverse team of experts in fluid mechanics, biology, and mechatronics.
By constructing their model at a scale ten times larger than that of krill, which are typically the size of a paperclip, the researchers utilized primarily 3D printable components. Additionally, the design of Pleobot is open-access, enabling other teams to employ it in the investigation of metachronal swimming, not only for krill but also for organisms like lobsters.
In their published study, the research group unveils a solution to one of the many enigmatic aspects of krill swimming: how they generate lift to prevent sinking while propelling forward. As krill are slightly denser than water, they would sink if not continuously swimming. To counteract this, they must create lift even while swimming forward to maintain their position in the water column, explained Oliveira Santos.
"We managed to uncover this mechanism through the utilization of our robot," stated Yunxing Su, a postdoctoral associate in the laboratory. "During the power stroke of the moving legs, we identified a significant effect—a low-pressure region at the posterior side of the swimming legs, which contributes to enhancing the lift force."
In the forthcoming years, the researchers aim to capitalize on this initial success by further refining and evaluating the designs presented in the research article. Presently, the team is actively working on integrating morphological features of shrimp into the robotic platform, such as appendage flexibility and the presence of bristles.
The work was partially funded by a NASA Rhode Island EPSCoR Seed Grant.
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