Winch and lever mechanism for spanning four crossbows
A geared drum-and-lever system by which 20 men develop the force to load four large crossbows.
The note works out the mechanics of a machine for spanning large crossbows: a winding drum one-third thick gathers one braccio of rope at each full turn, giving a thirty-to-one ratio between a five-braccia lever and its one-sixth counter-lever. Leonardo calculates that 20 men weighing 4000 pounds pressing on the lever exert 120,000 pounds on the counter-lever, enough to span four crossbows at once. The drawing shows a great spoked and toothed wheel turned by a crank and worked by a crowd of figures, set in a landscape with mountains at the left.
On this page
Great toothed wheel turned by a crank
The sheet is dominated by a large spoked wheel with a toothed rim, mounted on a heavy axle and turned by a crank at its hub. A crowd of small figures presses on the mechanism at the upper left, driving the winding drum that draws in the loading cord.
Thirty-to-one lever ratio
A winding drum one-third of a braccio thick collects one braccio of rope per revolution. With a five-braccia lever (thirty sixths) working against a one-sixth counter-lever, the mechanical advantage is thirty to one.
Force sufficient to load four crossbows
Twenty men weighing 4000 pounds at the head of the lever develop 120,000 pounds on the counter-lever. Leonardo judges this sufficient to span the four heavy crossbows served by the machine.