In the words of the classic video game Stronghold I can finally proclaim "Ballista ready". Here it is from the top:
From front:
And detail from front at a slight angle:
I unfortunately did not have time to shoot it yet, but will in a couple of days. Even so, I've already learned a couple things.
First, current pretension level is definitely about as high as I can with nylon. Even at mere ~45 degree washer rotation rotating the arms is quite challenging. This is partly because cones are now of correct length, 11 dactyls, and partly because of higher pretension. This is both good and bad:
- The force-draw curve should be about as good as it can ever be. Torsion spring stack should minimal torsion spring stack.
- There's the risk that tuning the two torsion springs to match in power may be challenging.
The metal spanner I made for the previous incarnation of the cheiroballista continues to work fine. Rotating the washers to 90 degrees was fairly easy, and it is highly unlikely I can even use that amount of rotation with this spring configuration.
The new case-slider dovetail construction is a much tighter fit than the previous one, yet it works very smoothly. The locking mechanism is at the moment identical to what I used earlier, as it worked really well. The handle is not designed to be pulled - it just locks into a simple 10mm pin.
The new field frames are extremely robust. The 5mm thick pi-brackets that have been riveted to field frame bars are exceedingly strong. The 8mm thick rings are very solid and help avoid the washer rotation problems I had earlier due to the old 5mm rings bending in the middle. The whole field frames/little ladder/little arch construction is very strong and fit is tight.
Before shooting I will make a lighter bowstring, as the current one is overly thick based on earlier rounds of shooting, and it may stress the bars in the cones too much. I will also create a couple of extra handles and improve the auto-locking property of the handle versions that are not meant to be pulled back with hands.
After the next round of shots I will move to experimenting with other spring cord materials, primarily horsehair and sinew. As discussed earlier, doing this on a small scale makes most sense, especially because processing sinew is so slow.