Rob Shepherd’s research team is building a jellyfish robot powered by hydraulic fluid to monitor the ocean. Image: Xu Liu and Science Advances
Rob Shepherd, professor of mechanical engineering at Cornell University, wants to make agile robots that can operate untethered for longer — and he’s using hydraulic fluid to do it.
“Hydraulic fluids are a great way to get high power output from robots, but people prefer to use batteries powering dc motors,” he said. “I started making the hydraulic fluid also a battery. That led us to making a fish that swims underwater hydraulically, where you hydraulically actuate a soft member, which bends, and then that hydraulic fluid powers the pump that’s causing the hydraulic fluid to move. We called it robot blood.”
If you’ve ever seen the first Alien movie where the traitor android named Ash gets decapitated and a milky-white liquid pours out of its body, then you know the inspiration behind Shepherd’s robot blood.
“But this fish we made, it wasn’t designed well. It weighed a lot and didn’t have that much hydraulic fluid,” he said. “What I like to talk about is the system’s energy density — how much energy per gram is in the robot — and I want to get up to 90% of the weight of the robot as energy storage. That brings us to the jellyfish because the jellyfish is mostly water, so we could make the weight of the robot be mostly battery and hydraulic fluid.”
Batteries are heavy. Therefore, designing multi-purpose components can make solutions more lightweight.
“It can change some people’s perspective on when a hydraulically actuated machine is a better choice because now the weight is also providing the electrical power to the system,” said Shepherd.
Hydraulic fluid actuates the jellyfish like a balloon that inflates and changes shape, and a gear pump and motor pull a wire that moves the fluid.
Shepherd’s jellyfish robot uses a liquid electrolyte from a redox flow battery as both a hydraulic fluid and electrical energy storage. Image: Xu Liu and Science Advances
His team also made a worm with five segments or pods, each actuated by a motor and a tendon. The motor and tendon compress the pod, and an incompressible fluid, acting as a hydrostatic skeleton, provides stiffness to the pod proportional to the compression. This motion creates an undulating effect and, along with Shepherd’s battery system, allows the worm to travel untethered longer than many other worm-like crawlers. This is useful for pipe inspection applications with complex networks.
Shown here is the design of a modular pod for self-contained actuation in soft robots. The actuation mechanism of the pod mimics the hydrostatic skeleton of a worm. Image: Chong-Chan Kim and Advanced Materials
As for the jellyfish, the design is a stepping stone along the pathway toward building something bigger. The current design can hold four liters of hydraulic fluid. The more hydraulic fluid that’s used, the more energy it transmits. So, the bigger the team designs the jellyfish, the more sense it makes.
“That jellyfish is what’s called a Lagrangian drifter, and it has basically the same density as the ocean. So when there’s a current, it can follow that current and monitor the health of the ocean, and then it can choose to come up out of the current, transmit its data, and then go back down into the current,” said Shepherd.
His team is also designing a larger fish, approximately three meters long with 30 liters of hydraulic fluid. This design has an efficient swimming motion that should be able to swim for weeks at a time, where the ocean recharges the battery.
“We’re going to orient it vertically, and then have the waves pump the liquid through a turbine inside of it and recharge the battery. That is going to take weeks to recharge, but what’s it doing anyway? May as well sit there and recharge,” he said.
For now, this jellyfish robot’s primary purpose and application is carbon dioxide (CO2) sequestration and monitoring in the ocean.
“There’s a huge effort to sequester CO2 at the bottom of the ocean, but it’s kind of catastrophic if you put it all down into one place and then it all comes out at once,” said Shepherd. “So, being able to persistently monitor all those CO2 sinks is what we’re trying to build it for. It can patrol the different areas in perpetuity and make sure there’s no CO2 leakage.”
Cornell Engineering
engineering.cornell.edu
Sources:
- Soft, Modular Power for Composing Robots with Embodied Energy
- The multifunctional use of an aqueous battery for a high capacity jellyfish robot
Filed Under: Featured, Fluid Power World Magazine Articles, Fluids