South Korean Quadruped Robot Shatters Endurance Records with Marathon Finish

A four-legged robot named RAIBO2 has achieved a significant milestone in robotics by completing a full marathon on a single battery charge. The machine covered the 26.2-mile (42.2-kilometer) hilly course in South Korea in just over 4 hours and 19 minutes, marking the first time a quadruped has finished an official marathon-distance event without recharging.

The achievement, which occurred during the 22nd annual Sangju Dried-Persimmon Marathon, was detailed in a study published on September 23 in the journal Nature. While four-legged robots are capable of navigating difficult landscapes such as stairs and rugged trails—areas where wheeled machines falter—they have historically struggled with endurance due to the high energy costs of supporting body weight and stabilizing movement across multiple joints.

RAIBO2 faced a challenging course featuring two 50-meter elevation climbs and slopes of up to 10 degrees. Scientists noted that these gradients placed substantial strain on the robot’s battery management system. This success followed an earlier attempt where the robot’s battery depleted around the 23-mile mark; developers attributed that failure to frequent pace adjustments required to match human runners.

To address these issues, the research team increased RAIBO2’s battery capacity by 33% and refined its control system. They implemented joint-stiffness control at the actuator, allowing the robot to soften its legs upon impact or provide stable push-offs. These modifications expanded the robot’s maximum range to 41.6 miles (67 kilometers) on a single charge on straight paths.

The study highlighted RAIBO2’s total cost of transport, a metric measuring the energy required to move a body over a given distance. The robot achieved a score of 0.25, surpassing the human benchmark of 0.37 and making it the first quadruped robot to exceed this efficiency figure. Researchers credited this performance to lightweight mechanical components, a low-loss motor-driving circuit, and a locomotion policy optimized for energy conservation.

The robot’s locomotion policy was trained using a simulation environment called RaiSim, which models various terrains including slopes, stairs, and icy roads. Similar to electric vehicles, RAIBO2 can regenerate battery power through kinetic energy capture during downhill travel, helping to offset the energy expended while climbing.

With a total battery capacity of 2,016 watt-hours, RAIBO2 possesses more than three times the travel range per charge of existing quadruped robots. The developers estimate the robot could travel up to 15.5 miles (25 kilometers) farther than its marathon distance, reaching its full 41.6-mile potential. This leap in endurance could expand the utility of quadruped robots in disaster zones and mountainous regions, where they could carry cameras, sensors, or communications equipment across uneven terrain where wheeled models are impractical.