Anti-scaling defence engine for a bastion
Geared rotating arms to keep attackers off the wall, with a beam-fixing detail
A large timber engine set on the roof of a defensive bastion, driven by a wheel of 100 teeth that meshes with a ten-tooth pinion, so that one turn of the wheel spins the pinion ten times. Four long rotating arms (each at least 16 braccia) sweep over the wall to prevent anyone from climbing the bastion. A second sketch below shows a method of fixing a strong beam firmly into a wall. Mirror-script notes accompany both drawings.
On this page
Wheel-and-pinion drive, 100 teeth to 10
The engine is powered by a large toothed wheel meshing with a small pinion (the rocca). The wheel carries 100 teeth and the pinion 10, so a single revolution of the wheel drives ten revolutions of the pinion. A tall vertical shaft carries the motion up to the rotating arms above the building.
Rotating arms guarding the bastion
Four long antennae radiate from the top of the shaft and sweep over the bastion's wall. Each arm is to be at least 16 braccia long. The device is meant to keep the bastion clear so that no attacker can climb up to it.
Gear ratio as a proportion
The 100-to-10 relationship between the teeth of wheel and pinion fixes a ten-to-one speed ratio. This proportional gearing multiplies the rotation delivered to the sweeping arms tenfold for each turn of the wheel.
Fixing a strong beam into a wall
A separate lower sketch demonstrates a way to anchor a heavy timber securely inside masonry. Stepped members interlock with the wall so the beam is held fast.