The steam locomotive put the power of the mill on wheels and shrank a continent. This one is a late-1920s express passenger engine — a 4-6-2 “Pacific” — modelled true to scale, one metre for one metre, with its cladding stripped away so the whole path from fire to motion is in view. Coal burns on the grate in the firebox; the heat is dragged forward through a nest of tubes that boil the water around them; and the dry steam gathered at the top of the boiler is stored, under about fifteen bar, as a coiled spring of energy.
Nothing here is animated by hand. The wheels roll a real distance, the crank pin sweeps a real circle, and the slider-crank is solved from its geometry: the piston shoves the crosshead, the main rod turns that shove into rotation, and coupling rods share the grip across all six driving wheels. Above each cylinder a piston valve — driven by a simplified Walschaerts gear, set a quarter-turn ahead of the crank — admits live steam to one end while opening the other to exhaust. Switch on the cutaway and the boiler, firebox and cylinders open up: vermilion is live steam pushing, blue is spent steam leaving, and the exhaust beats fire up the chimney four times a wheel turn — the chuff that drags the fire brighter the harder the engine is worked.
Drive it from the footplate. The Regulator sets how much steam is admitted; the Reverser sets the cut-off — how far into each stroke steam keeps flowing — so you pull away in full gear, then notch up toward mid-gear to let the trapped steam finish the stroke by expanding, saving coal. It is the same discipline of controlled, timed power you can build a gate at a time in DigiSim’s labs — here worked out in fire, water and forged steel.
Specifications
- Type
- 4-6-2 “Pacific” express passenger, c. 1928
- Mechanism
- Slider-crank + Walschaerts valve gear, solved from geometry
- Boiler
- Fire-tube, ~15 bar; driving wheels Ø 2.0 m
- Simulated
- Valve events, cutaway steam flow, live gauges
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