Anybody catch the show on TLC? Yea, Gods! What an impressive beast!It’s too bad they didn’t get to fire it more times! Would have loved to have seen what happened when the ball hit the wall.One of the things I don’t understand is that if they wanted an elastic rope, why didn’t they use bungee cords? Still, waaay cool to watch 'em build the sucker and fire it!
Didn’t see it, but the device appears to be a ballistae? You couldn’t store nearly as much energy in torsion bundles made of bungee cords, precisely because they’re springy. Fibre rope is much better. The throwing arms only move through about 90 degrees of rotation. Can you imagine how tight you’d have to wind a bungee cord before it would release a significant amount of energy in just a quarter turn?
Ballistae and onagers are okay, I guess, but trebuchets are more fun. 
Well, they wanted something like sinew, but only looked at fiber ropes. They kept complaining that they couldn’t find anything “springy” enough, which is why I was screaming at the TV, “Bungee cords!” I didn’t even hear them say why they didn’t want to use bungee cords, they just kept looking at rope.
Bungee cords aren’t springy in the right way. :shrug: When stretched, they release their stored energy over a long distance. What you need in this case is something that is springy, but only over a tiny distance.
I’ve taken a hankering to hurling, but though I’m more interested in gravity devices than torsion devices, it’s obvious enough that bungee cords would really suck for the purpose. If memory serves, the Romans preferred rope made from human hair for torsion bundles.
I think that it was fairly clear that the program was aiming for authenticity. Sinew would have been used in the original, but could be used in the reproduction because it simply is not available in sufficient quantities. So, they looked for a modern material as close as possible to sinew - as opposed to looking for the material that would do the job best. In the event of course, they should have chosen differently.
The arms on a Ballista rotate through rather less that 90 degrees - perhaps just 50 to 60 degrees at the most. The re-enactment society of which I am a member has a relativey small balista and catapulta. I am sure I remember somebody telling me that one reason why we use synthetic fibre in the reproduction was due to insurance problems. These machines are dangerous and it is necessary to use rope of know characteristics.
I’d think that the solution would be to build the thing any damn way you wanted, load it, point it at the insurance agent and ask, “How much did you say the premium was going to be?” 
You do bring up a good point, though. I hadn’t thought that the rope properties would be better understood than those of bungee cords.
Quite right about the range of motion on ballista arms. I was thinking it would be an onager when I wrote my first post (and onager arms indeed have about a 90 degree movement), then decided to look at the link only to find a ballista, and I guess I wasn’t careful enough in editing.
It turns out that a combination of sinew and hair was used. Cite. Guess my memory isn’t completely shot after all.
Look, you can try making one of these using bungee cords, but I flat out guarantee you it won’t have anywhere near the power of even run of the mill nylon rope. Bungee cords just don’t store energy in the correct fashion.
Oh ya, hence the Roman power tools and special milled brass washers and jacks they were using on it.
I thought this show was INCREDIBLY lame. I love the idea of “experimental archeology” (trying to figure out how ancient people did things and recreate them), but jeezopete, these folks drove me nuts! Putting on braces and not taking into account the fact that it would limit the travel of the trigger??:smack:
Not expecting the ropes to stretch when tension was applied to them???:smack:
Compared to the PBS series of a year or so ago where they built the trebuchets (and actually HIT) the wall they were aiming at) and did other Very Cool Things, this show was a waste of time.
YMMV, of course.
Archergal, I completely agree with everything you said. That trebuchet episode was wonderfully done. Also well done was the Discovery Channel’s episode on erecting an Egyptian obelisk.
Munch, did you see any of the other episodes in that PBS series? They recreated a rope bridge in the Andes, like the ones the Incans made. They recreated a small version of the Easter Island statues and moved it into place. They built some kind of special bridge like they use in Japan (I think, unless it was China). And they built a Roman bath.
It was an awesome series.
It was a wooden rainbow bridge in China, Archergal.
I’ve seen the Incan rope bridge before. Pretty cool. That was several years ago, wasn’t it? I wanted to see the rainbow bridge, but missed it (that’s where they basically weaved the bamboo together, correct?). I also missed the bath.
This program was shown in the UK some time ago, so I’m not sure that I remember all the details clearly.
My point about the rope was that, unable to use original materials they had to compromise: the looked for rope that had characteristics as close as possible to the original material; they did not look for rope that modern engineering told them would work best. In the event of course, the rope they chose was a poor choice - they had to use the jacks to make the catapult work at all.
There is nothing wrong with using power tools in experimental archaeology, it is only the end product that is being tested not the means of production. It would have been nice to have had gangs of adz weilding workers slaving away for weeks, but realisticly it is a case of use modern tools or dont do it all. Of course, once you know that a design basicly works THEN you can test to see if it can be made with ancient tools.
I must admit I did wondered about the washers. I don’t see how ancient technology could have made them to that standard. Polishing is one thing, but getting an exactly flat surface is quite another.
This particular show was a bit lame simply because the designers did not seem to have done their job properly. Couldn’t they have build a small model first?
Nope, no bamboo. It was a wooden bridge, but it is constructed in a way that simulates an arched stone bridge. It was actually very interesting and there were various arguments between some of the designers about where the weight would be distributed on this type of bridge.
Actually, it wouldn’t have been all that difficult to do using Roman technology, assuming that they had the know-how. There’s a process called “lapping” in which one takes basically a sharpening stone like those used to sharpen knives and rub it over the surface of the of the washers. You coat the surface with a dye to tell where the high and low points are. You keep doing this until you get the surface as flat as possible (generally within a few thousands of an inch). It’s a time consuming process, but a skilled craftsman can end up with a final product that’s almost as flat as any modern machine can produce. (You can even do it without using the dye, but the dye makes it a lot easier.)
Tuckerfan: Interesting note about lapping. I guess that is how bronze mirrors were made in ancient times - and there were certainly plenty of them.
Thanks for the correction, Neurotik. Whenever I have a binary choice (up or down, left or right, China or Japan) I invariably pick the wrong one. 