Static stability versus dynamic stability

There are two very different ways to stay upright. Static stability means the robot's center of mass stays directly over its support polygon (the area enclosed by its feet) at all times. A robot walking with static stability can, in theory, freeze mid-step and remain standing, which is slow and cautious but simple to reason about.

Dynamic stability throws that safety net away. The robot lets its center of mass move outside the support polygon for brief moments, trusting that the next footstep will land in time to catch it. This is how humans actually walk, and it's faster and more efficient, but it means a dynamically stable humanoid can't just stop mid-stride without a plan; it has to keep moving or actively recover.