The Patient Train
Ten wheels and two hundred and seventy teeth, and not one of them in a hurry. Scroll to wind the great wheel and watch the motion pass from hand to hand, each wheel answering the last in the opposite direction.
Scroll to drive the train, or take hold of any wheel and turn it by hand.
i · the driverThe Great Wheel
Forty-eight teeth cut from a single rolled sheet of yellow brass, crossed out with six windows to keep it light. It turns the slowest of all and carries the most weight. Everything else in the train is just this wheel's patience, divided.
Your scroll is its mainspring. Each line you read moves it a third of a degree.
ii · the first divisionCentre Pinion & Wheel
A twenty-leaf pinion of hardened steel takes the great wheel's motion and turns it 2.4 times faster in the opposite sense. Its partner, the thirty-two tooth centre wheel, carries the motion up and to the left, towards the quick end of the train.
iii · the long way roundIdler & Fourth Wheel
The idler sets nothing to time. It is there to turn the direction back again, so the broad fourth wheel below runs the same way as the centre pinion that feeds it. Watchmakers call such a part honest: it changes nothing except which way you are facing.
iv · where it quickensThird Pinion & Escape
Up at the top of the train the wheels are small and fast. The twelve-tooth escape wheel turns four times for every single turn of the great wheel, which is the speed at which brass starts to sound like a heartbeat.
v · the outridersMotion & Winding Wheels
Two wheels hang off the great wheel's other side. The motion wheel would one day carry the hands, and the winding wheel takes the key. They turn only a little quicker than the great wheel itself, and they ask very little of the wheel they lean on.
a note on meshingWhy the Teeth Agree
Every wheel here shares one module, so its pitch radius is simply r = m·N / 2, and two wheels mesh when their centres sit r₁ + r₂ apart. Each one turns at −N₁/N₂ times its neighbour's speed and starts offset by half a tooth, so that tooth always meets gap.
No tooth in this train ever passes through another, however far you scroll.