An Advancing Bridge Thrust Forward by a Windlass
Side, front and overhead views of a bridge driven on rollers by a pulley, windlass and chain
The page works out a bridge that can be thrust forward on the level by a windlass. Schematic side, front and overhead views show the deck advancing on rollers, driven by a pulley at a and a windlass at b through a chain that runs in a channel beneath a floor of slabs marked cn. Leonardo distinguishes bridges that carry their rollers along with them from better ones that ride forward over rollers left fixed in place. He also marks how far the deck projects beyond the wall, from a to b, against the part b c that remains within.
On this page
Windlass, pulley and chain drive the advancing bridge
The mechanism uses a pulley at a and a windlass at b. The deck cn is a floor of slabs with a channel underneath through which the driving chain passes, allowing the bridge to be thrust forward on the level.
A bridge that advances over fixed rollers beyond a wall
Some bridges carry their rollers along with them, but better ones advance on top of rollers that remain fixed in one position. Segment a b is the part of the bridge that projects outward beyond the wall, while b c is the part that stays within.