The new spanner for tightening the bundles worked like a charm.  We now have total control over how to put pre-load into the springs.  More on that in a moment.  For now, here is some video of the Orsova reconstruction shooting a 3/4 lb. bolt at half draw into my trusty catalpa round.

Click here for video,  field-test-3

Considering that we are only at 34″ of draw with 29″ more to go,  and the dynamometer is showing 2100 lbs of pull weight, I am starting to think an electric winch maybe the way to go when we get into the high power testing.  At least we can be out of the way if a limb decides to go all weak-minded on us.  A more authentic hand powered winch can come later.  It is clear why the Romans used a full steel backing for their ballista limbs.  I doubt that the current set will make it to full draw without breaking.    Just looking at them, I am guessing the bolts in the above video are only going around 200 fps. The chronograph arrived today, so we should be able to accurately quantify some of these low power results this weekend.    It is interesting to note that in the first field test we stopped at 1600 lbs of pull weight at 45″ of draw length.   With the new spanner tightening the bundles with another 15 degrees of rotation, we developed 2100 lbs of pull weight at only 34″ of draw when the above shot was made.  Clearly the pre-load put into the springs has a huge effect on the final performance of the machine.  More testing will no doubt find a viable balance between maximum power vs. spring longevity. 

Here is a photo of the new spanner and tightening procedure for the spring bundles. 


Even though all these shots are on a fairly timid, low power setting, the increased umpff from tightening the bundles can be seen by the increase in penetration into the catalpa log.  The two bolts on the right were from field test 1, the bolt on the left is from field test 3, after the new spanner had done its work on the spring bundles.  Now we are getting 3″ of penetration with a blunt 1″ tip,  rather than the 2 1/4″ we had before.  It will be an interesting comparison when we go to the smaller diameter Dura Europos style bolts, with sharp tips, and the machine cocked to full draw.   Perhaps not enough to pin an armoured barbarian to a tree yet, but it’s getting there.

One Response to “Zippyish Orsova bolts. New video.”

  1. "Warhammer1" says:

    I cannot help but cackle with glee while watching your vids, and cant stop reading and watching them. It is good to see you preloading the springs to tension as I suggested earlier, but wondered how you would overcome the string tensioning to accomplish this…

    I know that your blog must eventually end if I continue with reading and watching, but is something I do not look forward to…also have to wonder if you have performed optimization tests regarding bolt weight to pull. Often velocities can increased with a heavier bolt than a lighter one, and developing an optimization routine with the lower settings might help in finding an ideal bolt weight for full power testing…

    Awesome work!

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