Institute for Physical AI @ BMI · a demonstration
The body cannot stay up on its own; a loop keeps it there — sense, predict, step, a hundred times a second. That loop has one clean rule, and you already use it every day. Shove the robot on the board, and watch what it does first. The gold ring is where it has decided to put its foot — computed before the foot lands.
Provenance. The rule is the capture point (the Divergent Component of Motion): model the standing body as an inverted pendulum of rate ω = √(g/z₀), and the single spot that stops the fall in one step is ξ = x + v/ω. If ξ still lies under the foot, the ankle alone holds it — no step. The board runs this live on the real printed humanoid; the ring is ξ, the foot lands on it. Numbers exact, the figure illustrative.