A small crustacean is the muse of Pleobot, a modular robotic solution for metachronal swimming
Often, more than you imagine, Science is inspired by the animal world for its innovations. Not only the discovery of the human body but also smarter and safer ways to investigate the marine meanders. And it is with this objective that Pleobot was born. The inspiring muse this time is the krill, a species of invertebrate marine organisms belonging to the order Euphausiacea: small crustaceans that are concentrated in particular in the cold polar waters. Scientists at Brown University have taken the structure of krill as an example to create a robot that can simplify underwater exploration and locomotion, to discover more of what the oceans contain and, who knows, even identify other non-terrestrial living species. In fact, an artifact organism would not need much to analyze soil and subsoil in other worlds, with the right precautions and customizations (for example, to overcome temperatures that are not exactly “favorable” for certain planets). The team, led by Sara Oliveira Santos, a Ph.D. candidate at Brown’s School of Engineering, studied krill extensively to develop Pleobot, which can emulate the crustacean’s movements and unique characteristics.
How Pleobot was born
Krill are creatures that excel at swimming, braking, turning and acceleration. The navigation technique, called “metachronal”, involves the coordinated movement of several appendages or legs in sequence, creating an undulating movement that pushes the body forward. Thanks to the technique, krill can live in different and complex oceanic habitats and make great migrations. In addition, its build allows for considerable maneuverability.
“Experiments with organisms are challenging and unpredictable. Pleobot allows us unprecedented resolution and control to investigate all aspects of swimming that krill excel at underwater maneuvers. Our goal was to design a comprehensive tool to include all the details that make the crustacean one of the most athletic swimmers in nature,” Santos said.
The construction of Pleobot involved researchers expert in fluid mechanics, biology and mechatronics. The robot was built on a scale ten times the size of krill, which is typically the size of a paper clip. The device primarily consists of 3D printable parts with active and passive actuation of the joints to create natural kinematics.
How the little robot works
The scientists used force and fluid flow measurements and biological data to establish the relationship between the appendage and thrust. Basically, the team built Pleobot to have three moveable sections, replicating metachronal swimming. Researchers can control Pleobot’s two leg segments and have passive control of its biramous fins, which replicate the opening and closing motion observed in the minnow’s fins. The goal is to simulate how krill generate lift as they swim forward to avoid sinking as they are slightly heavier than water. Even when not swimming, animals must create lift to maintain their position in the water.
How Pleobot works
“We were able to discover that mechanism using the robot. We identified an important effect of a low-pressure region in the back of the swimming legs that contributes to the lift strength improvement during power stroke of the moving legs,” said Yunxing Su, postdoctoral partner in the lab and study co-author.
According to the researchers, Pleobot has the potential to harness millions of years of evolution in krill to produce an advanced ocean navigation robot.
“Aggregations of krill are an excellent example of swarms in nature: they are composed of organisms with a streamlined body, traveling up to a kilometer in each direction, with excellent underwater maneuverability. This study is the starting point of a long-term research goal that aims to develop the next generation of autonomous underwater sensing vehicles. Understanding fluid-structure interactions at the appendage level will enable us to make informed decisions about future designs,” said Monica M. Wilhelmus, who manages the Wilhelmus Lab at Brown.
In recent years, the growing need for remotely operated machines for underwater exploration has favored nature-inspired approaches. In particular, the discovery of extraterrestrial oceans motivates the development of new robotic platforms that will likely require the efficiency, versatility and maneuverability of metachronal swimming. As such, the Pleobot stands as a functional prototype that can be adapted to various instruments to further investigate underwater territories.
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