How are torsion siege engines any different from their flexion-based counterparts?

Question

I’ve been recently reading about ballistæ (and their many relatives!), and I’ve come across the assertion that early such weapons were tension-based (like any ordinary bow) while more advanced ones would work akin to a crossbow (torsion-based).

My question is: how the heck do the two differ after all? I can see that the energy-storage mechanism is fundamentally the same (pulled elastic string held back), and I thought it was about the different ways you could pull the string itself, but then I had a look at the Wiki page of the oxybeles (supposedly tension engine), which looks EXACTLY like a torsion ballista. Besides – don’t some crossbows get their string pulled by hand? Are those torsion weapons too?

Bonus: [these](https://www.stormthecastle.com/catapult/images/oxybeles-drawing1.jpg) two [images](https://www.stormthecastle.com/catapult/images/ballista-drawing1.jpg) attempt to explain the concept; I still don’t get it. Can anyone please explain it to me?

Thank you!

In: 8

Answer 1

Torsion is twisting, Make a rope and put it in a loop around two stick like [https://youtu.be/muFVYDyt_MY?t=543](https://youtu.be/muFVYDyt_MY?t=543) When turn the stick i around you will notice that it get harder and harder to do. Try that yourself at home with for example the legs of a chair. Be a bit careful because there is a force that pill the legs together too and you can break the legs of a chair. The stick you use to twist the top will spin around i you release is. Test it to get the principle do not twise it to hard.

That is how the one that is called a ballista in your images works, the amps that hold the sting do not bend and they use many loops of rope that are tensioned. So when you try to twist it a lot of energy can be stored with less than a quarter of a revolution.

You can see the replica in https://www.youtube.com/watch?v=RUBJY-oxeGk notice it is called catapulta. In Roman times a balista threw rock and could look like https://en.wikipedia.org/wiki/File:Ballista_(PSF)_vector.svg A catapult projectile that looks like arrows but larger, a spear is likely a better description.

The name gets changed during the medieval time and a Roman Catapulta became a medieval ballista

The one in your image that is called an Oxybeles has arms that bend, just a bow or a crossbow. It is fundamental a very large crossbow