Hardware

Power Density

Power density is the ratio of deliverable mechanical power to mass, typically in watts per kilogram, used to compare actuators and complete robots. Hydraulics historically led in raw power density, which enabled dynamic machines like early Atlas, while modern high-torque electric motors with low-ratio gearing now approach them with far better efficiency and controllability. System-level power density also depends on batteries, drives, and thermal limits.

Why it matters for physical AI

Dynamic behaviors such as running, jumping, and heavy lifting are gated by actuator power density, and battery plus actuator power budgets fundamentally shape humanoid and quadruped design trade-offs.