A quadruped robot designed to complete a marathon on a single battery charge.

Recent advances in legged robot control have expanded the potential for quadruped robots in real-world applications, such as rescue operations in disaster zones and mountainous regions1. However, practical deployment is hindered by the limited travel range per battery charge: a challenge compounded by the robots' inherent structural characteristics. Unlike wheeled robots, quadrupeds continuously expend energy at their joints to support body weight and incur kinetic energy losses during intermittent foot-ground contact. Moreover, optimizing energy consumption is complicated by trade-offs among various physical effects2, necessitating a holistic approach encompassing both hardware and software components. Previous research has predominantly addressed isolated aspects of energy loss3-6. Here we show RAIBO2, an energy-efficient quadruped developed through a comprehensive analysis of its overall energy-loss model. Efficiency is enhanced through a force-transparent, lightweight mechanical hardware, a low-resistance motor driving circuit and a low-energy-dissipation locomotion policy. RAIBO2 completed a full marathon in 4 hours, 19 minutes and 52 seconds on a single battery charge7, achieving a total cost of transport of 0.25: surpassing the human benchmark of 0.37. Compared with existing quadrupeds, RAIBO2 offers more than three times the travel range per battery charge. This breakthrough in energy efficiency paves the way for extended outdoor applications in which prolonged battery life is critical.