Institute for Physical AI @ BMI · a demonstration
A robotic fish, taken apart three ways: the body that swims, the one rule of moving through water, and the brain that sets its pace. This is the body — drag to turn it over, then take it apart. It has no rotor and no legs, yet it holds its depth for almost nothing; the reason is the water itself. The source on the right runs the real swimming physics, so it cannot lie to you.
Provenance. A body submerged in water feels an upward buoyant force equal to the weight of the water it displaces (Archimedes): ρ·V·g. Tuned to neutral buoyancy — the robot displaces exactly its own weight in water — that force cancels gravity, so the net vertical force is zero and holding depth costs no power at all. The water does what a drone's rotor must do continuously. What moving through the water costs is the next lesson. All numbers computed live by the Institute's open swim core. The 3D model is illustrative; the numbers are exact.