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What kind of rope is best for a ballista?

Would Nylon or Polypropene make a good torsion spring?Or would some kind of metal wire work better? By "better" i mean is able to produce the most force or is able to pack the most force into a 5/8"hole (thats the biggest drill bit i have).

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Which is most elastic ? Do some simple tests by hanging a piece of rope with a varying load and measuring it. I suspect a natural sisal rope might work very well.
+1

I don't know if it's the weave used or what, but in my experience, nylon rope stretches quite a bit under load, (far, far more so than hemp rope) implying that it has a very low spring constant.
meburnfire (author)  seandogue5 years ago
So nylon would make a very bad spring as it stretches, which means it isn't a good spring as it wouldn't be able to hold a constant amount of force whereas a hemp or sisal rope would work much better as a spring as it is able to keep its springiness for a longer period of time and hold it better?
Well, that's *my opinion, based on previous experience trying to use nylon rope for both pulling and suspending heavy loads. As I noted, it could be a weave issue, although I'm not sure.

It has been my experience that hemp rope is far less "stretchy", so I would think it would have a higher spring constant. I don't have enough experience trying to support any weight of consequence with sisal. My experience there is pretty much limited to tomato/cucumber cages and bundling sticks.

I was mainly +1-ing the "Do some simple tests by hanging a piece of rope...", since that's probably the best advise of all, short of a ballista expert chiming in.
meburnfire (author)  seandogue5 years ago
Well, i made the ballista and tested it... and i couldnt get enough sisal/hemp/manila at a reasonable price to make the second spring, and i found that nylon is actually pretty strong as after a while, it cant stretch and you can just tighten it. A lot.
rickharris5 years ago
In general the older weapons used animal sinews as springs rather than ropes. The Romans made Ballistas with hemp rope. But I would say nylon is going to be your best bet - Polyprop tends to neck and stretch under strain.