Double sling

"When you will have turned the wheels that twist the ropes, and you put the stick of the shapes."

This double catapult is one of the many drawings by Leonardo which describe and interpret the large medieval war machines.

Thanks to the movement of cog-wheels and worms, the ropes are twisted to hold and bring closer the two crossbows. Then the two poles are engaged and the machine is charged with stones. E single knock pushes down the rocker, which unhooks the two cog-wheels from the worms: the ropes instantaneously untwist and throw the stones.
Codex Atlanticus, sheet 152 1485-1490