> That's not recoil. Recoil is what moves a one tonne cannon back several
> metres when it fires a ten kg. ball. AFAIK confined to explosives
> based weapons.
Ah. Same term, different usage. You're thinking a specific, linear recoil; I'm using the term in a more generic sense applied to the Newtonian reaction to firing the weapon. Both are the "equal and opposite" reaction, the difference is in the direction of the reaction.
Ballistae (and crossbows) have a linear recoil, akin to gunpowder weapons. Rotational throwers have a rotational recoil.
> The movement you are describing is due to the disappation of energy
> caused by the whole of the energy of the descending weight not being
> transferred to the projectile.
Yes. The same reason gunpowder weapons recoil; part of the energy goes into throwing the ball forward; part of it goes into throwing the weapon backward.
>Similarly an onager tends to move
> forward as the arm hits the crossbar to release the shot.
Haven't had a chance to work with an actual onager; torsion engines are more complex than trebuchets.
> A properly designed platform can cope with these forces and even
> recoil.
Sure. I was just thinking that there are significant differences between a transport (designed to MOVE a siege engine) and an actual fighting platform designed to support it while it FIRES while moving.
>It's mostly dependant on the size of the weapon compared
> to the platform but also how solidly the weapon is attached to
> the platform. I believe small cannon were mounted on elephants
> in 18th Century India.
"small" being something like a 2.5 cm bore? The main problem with those was not so much recoil but the weight of the weapons themselves; they were juge compared to modern blackpowder weapons. You needed a platform to mount them on because they were too darn heavy for a single person to lug around and employ with much mobility.
> Whereas the forces you mention disappate within seconds.
Pretty much. Smaller trebuchet (say, 3m arm or so) are back under control within 30-40 seconds. Haul the long end down, latch it, and start working to get it reloaded.
Grimmund
--
"Your reality, sir, is lies and balderdash, and I am delighted to say
that I have no grasp of it, whatsoever!" - Baron Munchausen
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