The Ballista

Dodging in and out of the holiday festivities,  I was able to get a little more done on Firefly’s nether regions.

The pawls,  sight ladder and cocking levers are all that is left to be done on the winch assembly.    The latter will require their own set of pawls to engage the ratchet teeth.   If none of that makes any sense to you, stay tuned.   All will be revealed soon.

By “soon”,  I mean of course, in “catapult time”.  Einstein’s notion of time dilation has nothing on all us Earth bound catapult makers.  Days equal weeks.  Weeks equal months.  Months equal years. Very frustrating if you aren’t into long courtships and willful acts of gestation.

It occurs to me that this goofball blog hasn’t shown any videos lately.  These things come in stages and right now our little project is stuck in a non shooting phase.  Eventually this will end and we will get back to some serious catapultery.  In the meantime it may be fun to serve up some video highlights from 2010.

One of my favorites is this 7000 grain bolt delivering the goods at 312  fps to a 1/4″ steel plate, range 53 yards.  The  black stabilizing fins can be seen exploding in all directions.   Click for vid,  20100309103750(1)

Note the neat hole and heat striations where the square headed bolt  clipped the plate.

Or how about this one where my lousy shooting continued to take its toll on all and sundry.   Click for vid,  20100309124009(1)

Ouch! goes the utility trailer.

Then there was that pesky old concrete block that needed it’s innards seen to.   Click for vid,  20100313143734(1)

Punching through a compound archery target, a hay bale,  and an inch and a half of  Doug Fir at fifty yards,  even got the Rebecca’s attention.   Click for vid,  20100306160111(1)

Or that overhead shot showing the entire shooting sequence.  Click for vid,  20100622105903

And out of respect to Australians everywhere.  Click for vid,  20100323155804(1)

Or, how about balloon boy?   Click for vid,  20100323153608(1)

As accuracy got better,  Firefly tackled an old propane tank at 50 yards.   Click for vid,  20100624131007(1)

She even turned in some nice  seven shot, one hole groups before we had to move on and disassemble her for more improvements.

And then there was all that work to figure out a way to make modular springs that could be easily replaced and properly tensioned.  Click for vid,  20100203121555 .   Click for vid,  20100131192826

And don’t even get me started on the “chaffing trolls”.  That was horrible.

Inspired by Dr. Tracey  Rihll’s work in her book “The Catapult”,  we tried firing some lead bullets (glandes) out of Firefly.  At first we just attached a 14 oz. lead egg to the end of a bolt.  The results showed some promise.  Click for vid,  20100322154856(2)

Eventually we rigged a  double string and pouch and  Firefly started tossing true  glandes at the target.   They were less than impressive at first.   Click for Vid,  20100629172822(1).    But with work they started to increase in power.   Click for vid,  20100627140457(1).   And eventually they turned in  some credible performance on the fifty yard range tackling some sheets of 5/8″ plywood.   Click for vid,  20100701161210(1) .   Click for vid,  20100701182936(3)

At the top of her game with glandes,  Firefly performs a useful public service.   Click for vid,  20100720102955(1)

However, at her core , Firefly is a bolt shooter.  Exploring how some of  those deep craters in ancient fortification were made,  four inches of hardened steel slice into a concrete block.   Vid is in 4X slow motion,  20100317133432 .  And then there was all the work to extract it from the block.   It seems possible the Ancients enlarged those craters with a cold chisel as they retrieved their precious bolt heads ,  20100320123108(1)

And through it all, the irrepressible Rebecca has been the soul of patience and good company.  She even has her own research project,  modeling what may well turn out to be the original version of a torsion engine.     Click for the   XXX rated  vid,  20101116134729 .  The lounge lizard narration was just for you Melissa.

I guess that does it for now.   More stuff is in the works.  You should see the inside of my freezer.  So many pig’s heads.  Our long awaited forensic testing can begin in the spring.  ………. I wonder what helmet size that big one is?

When it came to it,  the laminated oak sections I’d intended for the drums didn’t stay so laminated during machining.  Bummer, I should have known that.   Shop husbandry and old glue are not the best of partners for facing the unknown.   No matter, the drums below are made from some billets of tight grained white ash and will do to get things started.

It seems logical to infer that inswingers probably had wider winches like this to reel in all the rope needed for their unusually long draw lengths.  It may well be that this one could be an inch or two narrower per side,  but given Firefly’s higher purpose as a research vessel  it seems better to build in some overcapacity rather than skimping and suffering the ignominy of reduced performance.  I suspect that when she is finished,  her total weight will be perhaps 20% higher than an original Roman machine.

Reconstructions like this are never perfect affairs;  after all,  one can hardly expect a firefly to light up an entire room (sorry).   I am not discouraged by these observations.  Time travel is never easy that first trip out.

Firefly’s tapered winch drums will be made from four sections of white oak laminated together.  I am counting on the oak being hard enough to hold up to the three strand rope that will be winding over it as the winch is operated.  At this stage I can’t see how it is not going to work just fine.  Still, best not to underestimate the enemy.  I will keep the tolerances on the axle hole through the middle of the drum  nice and tight.  Also the diameters on the ends of the drum need to be a snug fit inside the steel cups that are attached to the axle.   Both these things should equalize the pressure on the wood and help prevent splitting.

Judging from the smooth action of the axles in the bronze winch bushings,  it looks like the drums will pay out their windings very cleanly when it comes time to reload.  This is especially important for a one man operation of the machine and is the main reason I’ve eschewed any designs involving a block and tackle.  It is important  to be able to pull out the winch rope with a minimum of wrangling.   The last thing the Romans would want is a slow and clumsy winch in the middle of a human wave attack by a bunch of frothed-up barbarians.

I sense that the more we maximize for performance all aspects of the design within the limits of what the Romans could have made, the closer we get to the truth.   Any specific suggestion of what they “would” have constructed,  smacks too emphatic even for me.

Even the Catapult Gods overcame their aversion to the stench of gunpowder when this prodigy took the stage.

In some ways Annie was the first of the modern celebrities.    It seems sad that such precision and clarity have given way to the mush of mass produced marketing and entertainment.  Navel gazing is embedded in the stars.  Without manufactured luminaries,  vast sections of humanity would have no clue what to aspire to.   Surely it can’t all be new and awesome diets, new and awesome hair-dos,  new and awesome  exercise routines, new and awesome everything.

I suspect that I’m just steeling myself for the annual crop of New Year’s resolutions that are about to blanket the country.    Polish your own internal lodestone,  the rest is just decoration.

The simple minded mechanic in me sees these likely possibilities in the Cupid Gem. The  colorful annotation in the first plate may obscure some of the detail.  The second plate may be helpful for comparison.

First let’s get our bearings:   Arrow 1 is pointing at something that seems  to be pretty clearly the catch that holds the bowstring.

Arrow 3  is pointing at something interesting.  You can see it more clearly if you magnify and then tilt your computer screen back and forth a smidge.  ……… Yeah, that’s it.  A toothed side plate grinning out at you from antiquity.   How cool is that?

And now to it:   Arrow 2  could be pointing at a bolt.  ….. On the other hand perhaps it’s pointing to something a little more risque…..  Something you have to squint at with your imagination to see afresh:  the acutely angled string on an inswinger as it pulls the machine’s  limbs through their massive  120 degree  draw range?

Not buying it?  ….. Oh well, talking catapult smack is not all elegance and manners you know.   Concocting all this crap takes a lot of energy.  That’s why I usually give irresolvable controversies a wide berth.  All I can say is that my eyes tell me what my eyes tell me.  Cupid is hard at work cocking something.   Whatever it is doesn’t look  like any kind of outswinger I’ve ever seen.

Arrow 4 shows a rough concept for what the artist could have chosen to render if he or she had wished to show this depiction as an outswinger.     On the other hand, it may be that Roman perspective drawing wasn’t all I’ve cracked it up to be with my little black crayon.  This would be the point some valiant art historian needs to step in and settle this silliness.

One last point on the line drawing below:  given the truncated treatment of the bowstring as it becomes eclipsed by the starboard field frame,  we might suspect  even the mighty Marsden  glimpsed an inswinger here too.     (Yeah, Yeah,  I know.  They hadn’t invented them in his day…..urp.)

Click on the drawing for a closer look. Conclusion: A humble approach to historical inquiry  recognizes that we will only ever know an infinitesimal fraction of all that came before us.  Pearls, however,  are not always in the shadows.  Sometimes they can blind you with their obviousness.

Clearly I’m a besotted sop for inswingers.  How’s that for obvious?  Here’s betting a hipster like Cupid loved using one  to pierce the hearts of all those hard cases he had to deal with.

Not.

Pointed to the sky like she means it,  Firefly dreams of the day she can take a potshot at the moon.

The winch will gain a little more weight as the wooden drums and steel pawls are fitted.  Also the rear sight and a dorsal shaped shoulder stock will add a bit more yet.  All of this should move the center of gravity  back  perhaps an inch or two behind where she is currently suspended.  The stand will need to allow for this 45 degree angle so we can do some maximum distance shooting.

The plate below is from Marsden’s classic work, ” Greek and Roman Artillery”.     This original artifact shows little Cupid  working a double action winch similar to the one we are making for Firefly.  Note that the center of gravity on his machine is well back from the ladder and field frames.  If that kind of balance point is good enough for a Proto-God, I guess it will work for us.

While it is probably not the best practice to attach too  much precision to an ancient cartoon like this, we note that the likely way for Cupid’s ballista to balance where it does is for it to have a winch containing lots of nice heavy ironwork. Is this another data point favoring Firefly’s metal intensive winch?  Well, that’s just silly isn’t it?

My Dad used to tell me that a designer’s most valuable tool was the eraser on the end of his pencil.  This advice has proven to be invaluable to me as a tool and die maker running a one man shop.  Often there are multiple good ways to go about approaching a project.   As an individual,  the great trick  is to find the best of them without the benefit of a multi-brain sounding  board to build upon.  In my experience that usually means preserving as many options as possible before committing to a final and irrevocable choice.

In practical terms this means that often I only have a rough idea of where things are headed before a start is made.  Of course this approach only works if one has complete confidence that the foundation being laid down is versatile enough to support the variety of options that will no doubt present themselves as the work proceeds.   The weakness of this approach is that sequencing is everything.  Put the cart before the horse and the whole system crumbles into a unrecognizable jumble of poor planning and half baked flashes of discordant insight.

On the other hand, the great advantage of a fluid sequential approach is that the work that is completed can be used as a model to meditate on the next stage of design.  This is especially important if one is eyeballing the strength of materials and integrating them relative to the work that has already been laid down.  Firefly is largely a product of this approach.   I find myself wondering if the ancients didn’t use a similar methodology in constructing their catapults;  or did they have to submit detailed final plans to an uber-boss before work could begin?    Were their designs the work of inspired tinkerers or closely coordinated teams of designers and craftsmen working with bureaucratic exactness?  When it comes to Roman engineering, one suspects it was the latter.  Like so many things however, it was probably a combination of both.

As George Bernard Shaw observed, “The Golden Rule is that there are no Golden Rules.”

The limbs seen here are what might be termed “proof test” specimens.  They are built extra stout so we can explore the maximum draw weight possible with these springs (around 5500 pounds).  Our best efforts so far have yielded a consistent 330 feet per second and 1800 foot pounds of projectile energy when firing steel tipped bolts.  Further increases in performance will be inevitable if the limbs can be lightened to a significant degree.  Our old Gallwey ballista shot the very lightweight 1/2 pound bolts 700  plus yards.  Firefly should top 1000 yards when we get the new limbs installed.   It will be interesting to see what she can do with heavier projectiles.