Researchers from Cornell University have created a robot fish that powers itself with “robot blood“—a liquid of stored energy that circulates throughout the robot the same way blood circulates through our bodies. The “robot blood” is the battery that powers the robot’s applications for sophisticated, long-duration tasks.
The inspiration came from our own body’s complex integrated systems. The researchers wanted to mimic how humans store energy in fat reserves spread across the body, and an intricate circulatory system transports oxygen and nutrients to power trillions of cells. They wanted to make a robot with a more integrated system like ours because the way robots are now is very restrictive. They are completely segmented, with the battery in one spot, the motor in another, and so forth.
What they did was create a synthetic vascular system capable of pumping an energy-dense hydraulic liquid that stores energy, transmits force, operates appendages, and provides structure, all in an integrated design. The research was published in Nature.
Rob Shepherd, associate professor of mechanical and aerospace engineering, senior author of the study, and director of the Organic Robotics Lab, said, “In nature we see how long organisms can operate while doing sophisticated tasks. Robots can’t perform similar feats for very long. Our bio-inspired approach can dramatically increase the system’s energy density while allowing soft robots to remain mobile for far longer.”
Although engineers currently rely on lithium-ion batteries for their dense energy-storage potential, they are not an ideal option for form and flexibility. Solid batteries are bulky and therefore present design constraints. The alternative is redox flow batteries (RFB), which rely on a solid anode and highly soluble catholyte to function. The dissolved components store energy until it is released in a chemical reduction and oxidation, or redox reaction.
Soft robots that use hydraulic liquid are up to around 90% fluid by volume. Taking this into consideration, the researchers thought it would be a good idea if all that liquid could serve as a power source. By using that fluid to store energy, it would offer the possibility of increased energy density without added weight.
Shepherd said, “We want to take as many components in a robot and turn them into the energy system. If you have hydraulic liquids in your robot already, then you can tap into large stores of energy and give robots increased freedom to operate autonomously.”
To test this concept, the researchers created an aquatic soft robot inspired by a lionfish. It was designed by co-author James Pikul, a former postdoctoral researcher now an assistant professor at the University of Pennsylvania. A real lionfish uses undulating, fanlike fins to glide through coral-reef environments, and they made their robot behave identically.
They did so by using silicone skin for the outside and flexible electrodes and an ion separator membrane within. This allows the robot to bend and flex just as a natural fish would. For its internal systems, interconnected zinc-iodide flow cell batteries power onboard pumps and electronics through electrochemical reactions. The researchers were able to achieve energy density equal to about half that of a Tesla Model S lithium-ion battery.
The robot fish can swim upstream for more than 36 hours by using power transmitted to the fins from the pumping of the flow cell battery. This project proves that underwater soft robots offer tantalizing possibilities for research and exploration, especially since they are focusing on designing power sources that give robots the ability to function for longer stretches of time.
Shepherd thinks autonomous robots could soon be roaming Earth’s oceans on vital scientific missions and for delicate environmental tasks like sampling coral reefs. And in the future, these devices could also be sent to extraterrestrial worlds for underwater reconnaissance missions!
