Watt centrifugal governor

Two steel balls are mounted on hinged arms linked to a rotating vertical shaft driven by the engine. As engine speed increases, centrifugal force swings the balls outward and upward; through a collar linkage this motion partially closes the steam throttle, reducing power and slowing the engine. As speed falls the balls drop, the throttle reopens, and the cycle repeats. The system finds equilibrium where centrifugal force exactly balances gravity — and that equilibrium corresponds to the desired set speed. James Watt adapted this in 1788 from a windmill governor; James Clerk Maxwell's 1868 paper 'On Governors' analysed it as the first mathematical treatment of feedback control. The device is a physical analog computer that continuously solves the equation: throttle = f(ω − ω_set). Speed: continuous real-time (mechanical response time ~0.1–1 s). Capacity: single-variable set-point control; extends to multi-variable with additional linkages.