In 1788, James Watt bolted two spinning brass balls to a steam engine. When the engine sped up, centrifugal force flung the balls outward, closing a steam valve. Feedback control was born. Now: what if we scaled this up to regulate an entire city's 60 Hz grid frequency — a mechanical governor the size of a skyscraper?

The setup. Grid frequency drifts when load and generation mismatch. In the US, a 0.5 Hz drop means ~2% under-generation. Today, digital PLC systems open spillway gates or fire up gas peakers within seconds. Our mechanical version: two 500-tonne steel spheres on 200-meter arms, mounted atop a vertical shaft coupled to the grid via a synchronous motor. As grid frequency drops, the arms fall; as it rises, they lift. Their angle mechanically opens or closes hydraulic valves controlling a pumped-hydro reservoir.

Sizing the balls. Watt's governor works because centrifugal force scales as ω²r. At 60 Hz grid frequency, we can't spin the shaft at 3600 rpm — the tip speed on a 200 m arm would be 75 km/s (yes, kilometers per second), which is roughly 25× escape velocity and would shred any known material. So we gear it down. A 1000:1 reduction gives 3.6 rpm at the arms: tip speed v = 2π(200)(3.6/60) = 75 m/s, comparable to a wind turbine blade. Manageable.

Centrifugal force on each ball: F = mω²r = 500,000 kg × (0.377 rad/s)² × 200 m ≈ 14.2 MN. That's the weight of 1,400 tonnes trying to fling each sphere sideways. The support arm must resist this plus gravity — a steel truss roughly 3 m in diameter, tapering outward. Total structure mass: ~8,000 tonnes, comparable to the Eiffel Tower.

Sensitivity. The governor's job is to detect a 0.1 Hz frequency deviation (0.17% at 60 Hz) and translate it into valve motion. Ball height above the pivot follows h = g/ω² for a conical pendulum. At our nominal 0.377 rad/s, h = 69 m. A 0.17% change in ω changes h by 2·0.0017·69 = 0.23 m. Twenty-three centimeters of vertical ball travel per 0.1 Hz — plenty to actuate a hydraulic servo controlling a 500 MW turbine gate.

Response time. Here's where it gets ugly. The moment of inertia of two 500-tonne balls on 200 m arms is I = 2mr² = 4×10¹⁰ kg·m². To change speed, you need torque. If the grid tries to accelerate the governor by 0.1 Hz over 1 second, required torque is τ = I·α ≈ 4×10⁹ N·m. That's roughly the torque of 40,000 diesel locomotives. The mechanical inertia becomes a lowpass filter with a time constant of tens of seconds — worse than the human oscillations Watt himself struggled with, which caused early steam engines to "hunt" and eventually shake themselves apart.

The verdict. The physics works, sort of. It provides genuine synchronous inertia (which real grids desperately need as they lose spinning generators to inverter-based renewables). But it's a 100,000-tonne mechanical assembly doing what a $50 microcontroller does better, faster, and without the risk of catastrophic mechanical failure spraying 500-tonne steel balls across three ZIP codes.

The one honest use case: it would be an exquisite piece of civic sculpture. Watts's ghost gets a monument, and grid engineers get a Rorschach test.