The Future of Robotics: Why Endurance is the Next Frontier
By James Pikul, University of Wisconsin-Madison
Earlier this year, a robot completed a half-marathon in Beijing, clocking in at just under 2 hours and 40 minutes. While this time pales in comparison to the human winner, who finished in just over an hour, the achievement is still noteworthy. Many recreational runners would take pride in that time. However, what’s most revealing is that this robot required battery swaps three times during the race. This brings to light a significant issue in robotics: the challenge of energy.
Robotics: Marvels of Agility, Limited Endurance
Modern robots showcase astounding agility, replicating animal movements and executing complex tasks with methodical precision. Yet, they fall short in terms of endurance. Unlike living creatures, which tire from exertion, robots simply run out of power.
As a robotics researcher specializing in energy systems, I have been delving into how we can impart the staying power of living organisms onto robots. The traditional focus has been on enhancing battery technology, but what if we took a different approach? What if we designed robots that could "consume" energy like living beings?
The Need for Energy Solutions in Robotics
While robots have made leaps in movement capabilities—thanks to advancements in biomechanics and motor control—endurance remains a hurdle. For instance, Boston Dynamics’ Spot can operate on a full charge for merely 90 minutes, requiring close to an hour to recharge. This runtime is significantly shorter than the 8 to 12-hour shifts expected of human workers or even the multi-day endurance of sled dogs.
Issues with Current Battery Technology
Today’s mobile robots primarily rely on lithium-ion batteries, akin to those found in smartphones and electric vehicles. Though these batteries are dependable, their performance improvements are slow. Each new generation offers an average improvement of just 7% annually. At this rate, it would take a full decade to double a robot’s runtime.
In contrast, animals store energy in fat, which is incredibly energy-dense—approximately 9 kilowatt-hours per kilogram. To put this into perspective, a sled dog might carry 68 kWh of energy, resembling the capacity of a fully charged Tesla Model 3. Current lithium-ion batteries only provide about 0.25 kilowatt-hours per kilogram. Even highly efficient motors would require batteries dozens of times more powerful than what’s available today to match a sled dog’s stamina.
Constraints of Recharging
Recharging isn’t always feasible. In disaster zones, remote terrains, or during prolonged missions, access to power sources can be a rarity. While robot designers can sometimes increase battery capacity, adding weight compromises the robot’s speed and efficiency. For instance, the battery already accounts for 16% of Spot’s total weight.
Some robots have explored using solar panels, theoretically extending runtime in sunny conditions. However, solar energy delivers insufficient power for mobile robots, especially when rapid movement is involved. This makes solar energy more suited for stationary or ultra-low-power systems.
Impacts on Robotic Functionality
These energy limitations matter immensely. A rescue robot with a battery life of just 45 minutes may not last long enough to fulfill a critical mission. Similarly, a farm robot that needs to recharge every hour would struggle to harvest crops promptly. In environments like warehouses or hospitals, such short runtimes complicate logistics and elevate operational costs.
If robots are to integrate meaningfully into society—be it assisting the elderly, exploring hazardous environments, or working in tandem with humans—they must demonstrate endurance spanning several hours, not mere minutes.
New Frontiers in Battery Chemistry
Emerging battery technologies, such as lithium-sulfur and metal-air, show promise with theoretical energy densities much higher than those of lithium-ion cells. Some of these new technologies near the energy density of animal fat. When coupled with efficient actuators that convert electrical energy into mechanical work, robots could soon rival, or even surpass, the endurance of animals with low body fat.
However, these next-gen batteries come with challenges. Many are tough to recharge or degrade over time, and they face significant engineering hurdles in realistic applications.
The Promise of Fast Charging
Fast charging technology is making strides and can potentially shorten downtime. Some new batteries might recharge in mere minutes as opposed to hours. But this rapid charging often results in trade-offs, straining battery life and requiring specialized infrastructure. Even with advancements, a fast-charging robot would still need to stop frequently for power, still relying on the core issue of limited energy storage.
Reimagining How Robots Consume Energy
In nature, animals don’t recharge; they consume energy through food. What if robots could mimic this process? By adopting a synthetic metabolism, future robots might convert energy-dense materials like metals into electricity.
Some researchers are exploring the idea of robots that can "digest" energy sources. For instance, chemical reactors could transform high-energy substances like aluminum directly into power. This innovation allows robots to gather energy sources autonomously, much like they pick up objects.
Advancements in Bioinspired Energy Systems
Other innovative approaches involve developing fluid-based energy systems that operate similarly to biological circulatory systems. A notable example is a robotic fish, which tripled its energy density by utilizing a multifunctional fluid instead of a standard lithium-ion battery. This approach effectively delivered the equivalent of 16 years of advancements in battery technology without even introducing new chemistry.
Robots constructed with bioinspired systems could operate for longer periods by sourcing energy from materials far more efficient than today’s batteries.
Beyond Energy: Comprehensive Systems for Robotics
In nature, the energy system serves multiple purposes beyond providing power. Blood regulates temperature, distributes hormones, combats infections, and aids repairs. Future robots, following this paradigm, might manage heat through fluid circulation or heal themselves with stored or ingested materials. Rather than concentrating energy in a single battery pack, energy could be distributed throughout the robot’s structure in limbs and soft components, thus enhancing resilience and adaptability.
The Road Ahead: What Lies in the Future of Robotics?
Today’s robots can move with impressive speed and agility, but they still lack endurance in a meaningful way. While advancements in technology have improved their cognitive and mechanical capabilities, associated energy systems have yet to keep pace.
For robots to become integral allies in human-focused tasks, we must focus on establishing a robust energy framework that provides them with not just intelligence and dexterity—but also the endurance they need.
Conclusion: Redefining the Future of Robotics
Robotic technology has advanced tremendously, yet we still encounter significant hurdles in energy management. As we push the boundaries of what robots can achieve, focusing on endurance and energy consumption strategies will be crucial. Should we manage to create machines that can "feed" as animals do, we may unlock vast new possibilities for robotics that could reshape industries and societal interactions. The next frontier in robotics is not merely about mobility and cognition, but about sustaining energy for prolonged operation in a world that demands more from these remarkable machines.
