[LT] Portcullises

[Anthony]

Originally Posted by Bruno

The mechanism has to lift the gate and the weight of the cables/ropes. A reasonably simple pulley mechanism is pretty efficient but requires significantly longer ropes (more weight and much more room to work in) or a winch, which introduces more significant mechanical efficiency problems if I've got this right.

A windlass located above the gate requires 1-2x the height of the gate in rope or chain and has a mechanical advantage equal to the ratio of axle diameter to crank diameter. Mechanical efficiency depends mostly on the quality of your axles, but your rope/chain is only passing through one or two axles, depending on how it's configured. If we want to convert 1 yard per second (walking speed) to 1 foot per 3 seconds, that's a mechanical advantage of 9, so one person at 60 lb force can handle 450 lb with a 20% increase for friction; a 900 lb grate would require two people. Depending on just how bad medieval axles are, you might need more people or more force.