Samuli Seppanen over at Ballista Wiki has seconded the use of Philon’s wedge system on Phoenix.  I’m kind of tickled that someone else gets where I’m coming from on this idea.  Here is the text of our conversation for any of you catapult nerds that may actually be reading any of this.  Samuli starts off….

“The idea of adding wedges on top of the crossbars is an excellent idea! They make even more sense for the Emporion ballista than the Lyon ballista – have a look at these pictures. The Xanten ballista (see Bibliography) also has flat crossbars, but they are not as wide as those in Emporion ballista. In any case the flatness of the crossbars seems to be quite common, if not universal, feature. One would think that rounding the edges of the crossbars would help prevent damage to the cords, but maybe that is not necessary in practice with sinew cord. Or maybe the crossbars did have wedges on top of them – the wider the crossbars were, the higher the wedges could be made. This widening would of course come at the cost of reducing the amount of spring cord one could insert. The topmost wedge could be rounded at the edges, so that it would not cut the cords while being tightened. I don’t think the wedges alone could have provided sufficient cord tension without a stretcher, but they could be used to drive a bit more tension into the cords without having to resort to rotating the washers.

Samuli.seppanen (talk) 09:02, December 21, 2015 (UTC)

Actually, now that I think of it, having wedges in the crossbars would also allow fine-grained matching of the springs without having lots of locking holes in the washers and the hole carriers; one could just whack a wedge slightly with a hammer if a spring was slightly too weak. The same could be done in reverse to loosen the spring a bit. The same could be done in reverse. That said, the small number of holes in the Lyon hole carriers/washers could also be explained with the properties of sinew as I tentatively suggested earlier. Not that these two ideas are contradictory in any way.

Once I reach the said 150 joules with nylon, I will start producing sinew cord, which will be a rather lengthy and dull process, even for a weapon of cheiroballistra’s size. However, it just has to be done, because it is the only way to say with (90%) certainty what the characteristics and the power of the real cheiroballistra were. Moreover, the results can be extrapolated to larger machines such as the Orsovo ballista.

I’ve already planned on making a reconstruction of the Xanten (manu)ballista after the cheiroballistra, primarily because it was found in excellent condition and the book dedicated to it (see Bibliography) has a complete list of dimensions, assembly instructions, etc. done in a very precise German fashion. So that project should be way more relaxing and much, much quicker than the cheiroballistra project that required so much work, testing, failures and dead-ends on my part.

Samuli.seppanen (talk) 09:19, December 21, 2015 (UTC)

 

And then I respond with my usual ebullience….

 

“…fine grained matching of the springs….”   Yes!   Finally I’m on the same page with someone whose work I respect.

The wear resistance of sinew couldn’t be much different than nylon.  It’s just a fiber afterall.  I have a pretty good idea of what kind of chaffing can occur on a high power machine.  A full radius on the crossbars is essential.  Just rounding their edges a bit just doesn’t cut it,  (Well actually it does, if you catch my drift.)

I am somewhat torn about including the counter washers.  (I’ve stopped calling them vernier plates as it makes them sound so invented and new, when really they are no different than counter washers on a wood machine.)  If Philon’s wedge system doesn’t work out for tuning I want some kind of back-up.  It’s not like I am making the claim that Phoenix will be a perfect replica of how the original must have looked.  This is the test-bed aspect of the work and not achieving a fine grained balance is just not an option on a precision shooting machine.

So anyway, the parsimony police will no doubt cap me for including them.  I’m just not comfortable with putting that much work into something and having no recourse if the Philon thing doesn’t work out.

In my experiments with Firefly I discovered that once a balance was achieved and the bolt was flying straight, it was possible to add more rotation to the washers (so long as it was done equally of course on all four of them) and the balance didn’t change a bit.  So here’s my hypothesis: because there are only 4 locking holes on the Elenovo field frames, start off with the washers locked into position at a reasonable​ low power setting, perform all the wedge adjustmemts to achieve balance, and then rotate the washers into a high power setting, maybe as much as 180 degrees or so.  I believe the balance may well transfer right through all that rotation.  If it can be shown to work, I could ditch the counter washers, and be back in the parsimony game with some high power to boot.

Anyway, that’s the plan. And I thank you for taking the time to understand where I’m coming from.  Nick.”       23:04, December 21, 2015 (UTC)

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