If we envision a future in which humanoid or animal-inspired robots work at construction sites or safeguard older adults, then we’ll need to develop energy storage systems that will allow those bionic beings to continuously operate for lengthy periods of time.
Bots like Boston Dynamics’ Spot move like a canine; the company’s humanoid Atlas model can run, roll and even perform cartwheels.
“There’s a lot of effort that goes into trying to mimic or reproduce similar types of functionalities as humans or animals. But energy is often ignored in that,” says James Pikul, an associate professor of mechanical engineering at the University of Wisconsin-Madison. “A core limitation of the capabilities of these robots is how much energy can they store? And how well can they provide energy from their onboard storage?”
In a review paper in the journal Science Robotics, Pikul and Yichao Shi, a postdoctoral researcher, explore the challenges and possibilities in trying to achieve animal-like endurance in mobile robots through emerging—and future—energy storage technologies.
Current mobile robots, much like other rechargeable electric technologies, rely on lithium-ion batteries, which have relatively low energy-density compared to biological energy reserves. They also require access to the electric grid for frequent recharging.
“We can’t simply just add more batteries, because that will just compromise their payloads,” cautions Shi, who earned his PhD in mechanical engineering and applied mechanics from the University of Pennsylvania under Pikul.
Pikul and Shi point to energy storage technologies such as lithium-sulfur and metal-air batteries, along with hydrogen fuel cells, as potential long-term options to bolster energy-density—though Pikul notes that they’re still in the research-and-development pipeline and are a decade or more away from practical applications.
His research lab is building systems that incorporate energy storage into the physical structures of soft robotics, facilitating mechanical movements in addition to providing electrochemical power.
With an eye on the rechargeability piece of the puzzle, Shi is working on aspects of a system that would allow robots to consume metal, such as aluminum, and extract energy to refuel themselves. Pikul’s lab is also investigating liquid and gaseous energy sources that could similarly provide on-the-go energy.
“I think trying to get robots to be able to ‘digest’ those types of materials is really an attractive way to get them to the autonomy levels of animals,” he says.
But, Pikul notes, humanoid or animal-like robots might not actually be the first places we’ll see next-generation energy storage technologies.
“Actually, a tractor is a robot. An autonomously flying airplane is a robot,” he says. “For these types of storage technologies, their first market might not be a humanoid robot but some other application where the energy advantage makes economic sense. And so that might be in, for example, a construction site or a short-range aircraft. And if that’s the case, then we may see it in five to 10 years. But I think it really depends on where the economic model makes sense.”
Associate Professor James Pikul, right, and his lab members, including postdoctoral researcher Yichao Shi, second from left. Photo: Joel Hallberg
James Pikul is the Leon and Elizabeth Janssen Associate Professor.
Top photo of Spot courtesy Jonte/Wikimedia Commons.