A brass driver gear turns a chain of six meshing gears; because meshed teeth must move at the same linear speed at their pitch circles, each gear's angular speed is inversely proportional to its tooth count, and neighboring gears always spin in opposite directions. Two of the larger gears carry eccentric cams that convert that rotation into the back-and-forth stroke of pistons inside fixed cylinders, mimicking a real steam-engine crank mechanism. Periodically, valves along the pipework vent puffs of steam, driven by the same clock as the rest of the mechanism.