The Ballista

Upon a closer inspection of our electric winch’s innards the cause of it’s failure became apparent.  The hot terminal connection out to the motor had been assembled without the use of a lock washer and the nut had backed off to the point the connection was very loose.  This in turn, created an intermittent connection that sparked enough to melt the insulating pad at the base of the terminal, which caused the smoke signal and contaminated the connection to the point the juice stopped flowing completely.  All fixed now.

The Kingdom is saved!   The lumbars rejoice!

At  4,500 lbs of draw weight  a curl of smoke started emanating from our Warn winch.  After that the little beastie refused to pull at all and I fear the motor may be toast.

The new block and tackle set-up was supposed  to keep things within the winch’s pull rating.   Oh well,  it seems the Catapult Gods are none too thrilled by our conversion to an electrically powered device. They always were a jealous lot when it came to preserving the old ways;  it’s not surprising their congregation got bored and shrunk to almost nothing as soon as gunpowder was invented.

In the meantime,  we of the “almost nothing” are forced to pursue our torsion goals by muscle power alone.  Given that this particular Warn product had problems before with a cast aluminum clutch that cracked (which they graciously replaced with a properly made steel one) I am rapidly coming to the conclusion that this particular piece of modernity is inferior to our purpose.  And if we can no longer trust Warn to make a decent winch from the get-go,  well, maybe their holinesses had a point after all.

In a world of dubious integrity, the way forward is often paved by digging up the way backward.

Here is a photo of the new design for attaching the struts to the field frames.

The yoke and cross pin directs the forces straight down the strut  to help eliminate any deflection of that member.   Our previous version did not straddle the lug in so balanced a manner.  Natural selection at it’s finest.

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And on another matter, it will be important to have a suitable reflector to bounce back the laser signal for our new range finder.   I am hoping that this five by seven foot, shiny space blanket will be large enough for the  laser to hit at a distance of over half a mile.   The blanket will need some kind of PVC, take-apart frame to mount it on.   Also,  judging from how wobbly I was last time out, trying to take the measurements off-hand is not the way to go.  The range finder will need to be tripod mounted to have any hope of engaging the reflector at Firefly’s maximum range.

And to all those wondering why I don’t just get on and shoot the bloody thing —  all in good time.  Rome was not built in a day.

That old 5/8″  strut perched atop our new 7/8″ version, looks to be a spindly little member now that we’ve made the switch to something heavier.

Also,  the new strut’s connection to the lug on the vernier plate is more sensibly made with a simple yoke and cross-pin, (the latter not yet installed).

While the old struts seemed to work fine for several hundred full power shots, something got out of whack and rather than just straighten them and carry on,  it seemed prudent to replace them with these hunky brutes.  It is funny how easily the “eye” can recalibrate itself to a new paradigm.     That skinny little 5/8″ strut just doesn’t look right any more.

And now we wait for the wind.  Or more specifically,  the lack thereof.

Because frolicking with catapults is such a cerebral activity for those of us devoured by the bug of making them , oftentimes brutal lessons will manifest as soon as we hit the firing line to see what our little creations can actually do.  Often this comeuppance takes the form of broken or twisted components that have succumbed to some form of ballistic ambition or personal incompetence.  Either that, or we lay content with mediocre or abysmal performance, in fear that our precious creations will explode before we have finished admiring them.

I have always adhered to the belief that if they don’t break, twist, or at least have a few grumpy spells, catapults end up being more decorative than functional and informative.   To this end, Firefly’s current upgrades are just another blip in a long succession of improvements that have made her progressively heavier, yet more powerful.  The end point of this development process must inevitably leave her in a state of rickety balance between those forces trying to tear her apart, and those that strive for a few more foot pounds of performance.  At the risk of pissing-off the Catapult Gods that hold sway in all such matters, I sense Firefly’s final state of “balance” is fast approaching.

The electric winch installation is almost complete.  The side opposite to where that shackle ties off the end of the winch rope,  will soon be equipped with an extra pulley to allow an additional fall of rope so that our 4700 lb winch can easily handle the 5,000 lb load.   This orange beastie doesn’t have quite the same terrifying clickity-clack as the hand winch, but the couch-potato aspect it provides will make data collection a much more pleasant and prolific experience.

While it pains me to admit it, there is a structural issue with the diagonal struts that needs to be addressed.  For a while now I’ve been fighting to keep the starboard limb from rising up laterally at full draw.   It is clear that the diagonal struts need to be made from a heavier cross section material as the 5/8  inch stuff we are currently using has a tendency to bow out when under load.  This allows the field frame to tip back slightly, the effect of which is magnified by the long arc of movement out to the limb tip.  You can just make out the bow in the strut in this next photo taken from the at rest position.

When it is under load the bow becomes quite pronounced.   One can only imagine how damaging it would be to the entire machine if the kind of loads we are running were attempted with no diagonal struts at all, as some researchers have suggested.  If a winch powered,  iron frame ballista,  is going to perform above the level of a glorified garden toy,  it is essential to stabilize the field frames back to the stock by triangulation with a decent set of struts.

It is by this argument that we infer the existence of the vernier plates on the original Orsova machine, because without those plates there really is no good place to attach the struts to the field frames.    Possibly a strut could be connected to a projecting length of tang from the kamarion,  but this would be a profoundly inelegant solution and not nearly so strong as a lug projecting from a vernier plate.   Of course,  a vernier plate also provides the necessary hole pattern to create the fine rotational discrimination of 7 1/2 degrees in the washer that is essential to balance the two torsion springs.  Also it provides the opportunity to utilize the maximum amount of spring cord by providing a rebated rim for the washer to rotate in, and thus allow the full diameter of the 3.1″ hole in the end caps of the field frame to be available to receive an increased spring diameter.  And in the words of Philon, from his manual on artillery, “The man who wants to shoot far must try to put on as much spring cord as possible…”

Very rarely is there only one good way to do something.  However,  having wracked my brains for years on this matter,  and now with this bowed strut and lifting limb situation, I am all the more convinced that the original machine must have had a sturdy set of struts and vernier plates to attach them to.

For any newcomers to this blog, here is a snapshot of Firefly belting out a 415 gram bolt to a range of  892 yards.  If you scroll back several pages we have  some videos and write-ups of all the action.   The four diagonal struts we are talking about are clearly evident in this shot.

All he said was “Urp!”,  and scanned the horizon for his next meal.   A starving man will eat truffles with as much regard as he will beans.   Sensibility is inversely proportional to necessity.

No more broom handle initiations for our trusty chrono.  Strictly the Ritz from now on.

A couple of tugs on the lanyard and the domed head on that long screw will depress the activation button, then this clever little instrument will start emitting microwave radiation for 30 seconds so that it’s radar sensor can make doppler measurements on the speed of  the bolt.   This chronograph has worked very well for us over the summer, and with this mechanical finger to get it started, it will be a huge improvement over the inelegant way we have been doing it in the past by fumbling around with a five foot pole like some drunken sailor stabbing at spiders.

Ain’t instrumentation cool?

The twelve sharps seen in this photo have an overall length of 36 1/4 inches.  This makes them equivalent in length to the famous clothyard shaft loosed by the medieval English longbowmen.  Of course, at an average weight of  521 grams ,  +/-  1/2 gram, they are about 10 times heavier than those worthy projectiles my ancestors were flinging at the French nobility back at Agincourt and Crecy, and could be cast over three times farther.  That is 80o plus yards for Firefly vs. perhaps 275 yards for a stout yeoman with his trusty yew warbow.  Apples and oranges to be sure,  but sharp pointy things driven by archaic stringed devices hold enough commonality to at least coexist in the same sentence for a while.  Beyond that, there is not much comparison.

In other popular units of measure, these bolts each weigh:  8,040 grains (+/- 7.7 grains), or 1.148 pounds (+/- .00088 lbs.)  It should be noted that  the low deviation in their weight was achieved by adding small amounts of lead shot into the socket of the steel head before gluing the shaft in place.

Our intent here is to explore the maximum potentiality for precision at Firefly’s longest range,  and for that a closely matched set of bolts is imperative.   The balance of the bolts has also been carefully controlled to 12.41 % FOC.  This number represents the “forward of center” balance point of the projectile and indicates how far the center of gravity is beyond the dimensional center of the bolt.  In this case the balance point is 4 1/2 inches forward of the 18 1/8 inch center of the 36 1/4 inch long bolt.  (That is: 4.5″ divided by 36.25″, to yield  .1241,  or 12.41 %)    This FOC  number puts our bolts smack in the favored range of  9% to 15% for optimum stability and range.

And as to how well that all works out, we should very soon discover.

As D-day approaches,  massive stockpiles of ammo pile up on the green fields of the Little Catapult Factory.   Being made from genuine polyethylene, these  eight inch fins are sure to give blue-stocking purists a case of the queasies.

Rawhide or maple fins will have to wait.  An analog is an analog is an analog.  “Perfection” to a reenactor is not the same as “perfection” to an experimentalist.  We make no claims beyond these obvious concessions to pragmatism, and, clearly, this fragment of our project is not disposed to authentic rendition.  That will be for another day.