Bio-Inspired Robot at Home Under Water

In the millions of years that moon jellyfish (Aurelia aurita) have existed, they have evolved into some of the world’s most efficient swimmers. That is why Erik Engeberg, Ph.D., associate professor in the Department of Ocean and Mechanical Engineering, chose them as a model for his lab’s newest invention, the JenniFish — a soft, stretchy, nine-tentacled, free-swimming robot.

The device will collect data on ocean health as it swims along the briny deep. Its nickname is JenniFish, for Jennifer Frame, a student who helped develop the original prototypes, and now works with the navy. Assistant professor Oscar Curet, Ph.D. helped design and evaluate the performance of the Jennifish.

The latest iteration of the robot is made of flexible, glow-in-the-dark rubber molded in a 3-D printed cast. Sensors in its microcontroller, or “brain,” detect its orientation and track water temperature, depth, and plankton and algae levels.

The JenniFish is the latest technology to emerge from Engeberg’s BioRobotics Lab, where he and his team research how biological entities and processes can be harnessed to create life-enhancing technology — a branch of science called bioinspiration. “You take traits of nature that took millions of years to evolve to a very sophisticated state, then apply them to artificial systems,” said Engeberg. “That’s what we did with the JenniFish.”

Ironically, given the live model’s aquatic talents, Engeberg’s greatest challenge was designing the JenniFish to swim. Moon jellyfish move through the water in two distinct ways: either they float along on ocean currents, or they propel themselves, by contracting their muscles to force jets of water out of their bodies, then relaxing their muscles as a second water vortex gives them another push forward.

The JenniFish uses both modes of propulsion. When launched into the Gulf Stream, the current moves the robot to another location, where it can drift-dive within the current toward features of interest, like algae or red tide. In self-propulsion mode, the robot’s actuators inflate with water, then three battery-powered pumps move the tentacles, allowing the robot to swim in three dimensions.

The difficulty lay in perfecting the interaction between the actuators and pump, and gauging how that interaction affected the thrust force the device generated while swimming.

“Interaction between the variables, along with the frequency and method of actuation, is very complicated,” said Engeberg. “Finding the sweet spot was really tough.”

The JenniFish’s greatest limitation is also its greatest strength. It is slow, just like a live moon jellyfish, whose efficient swimming technique only works at low speeds. However, slow speed provides two advantages to the robot. It enables long battery life and it minimizes damage if the device bumps into fragile underwater features like coral reefs.

Funding for the JenniFish comes from Engeberg’s own startup accounts and departmental sources. The device has already collected data on test dives along the ocean floor, but it’s still in its preliminary stages. With the help of a student, Dan Luvisi, future prototypes will collect data on the damage that climate change wreaks on coral reefs.

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