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.
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. Similarly an onager tends to move forward as the arm hits the crossbar to release the shot. I don't know if there's a special name for those forces.
A properly designed platform can cope with these forces and even recoil. 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. No reason to suppose ballistia couldn't be used the same way.
>> The time spent on regaining control is also trivial in the context of
>> reloading time of such weapons.
>
>Depends on the size of your firing platform, crew, and weapon. The
>different arm length provides leverage in both directions. Depending
>on the relative arm lenghts, 2-3 guys in armor can just *pull* down
>the arm on a half-ton trebuchet; reload time goes pretty quick, 2-3
>minutes. If you've got to *crank* it back down, longer, of course.
Whereas the forces you mention disappate within seconds. Indeed you don't start pulling the arm down until they have. So unless you've upset a living mount you'll regain control quickly enough.
-- Donald Oddy http://www.grove.demon.co.uk/
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