The Ballista

As Firefly moves closer to completion it seems appropriate to examine her intellectual underpinnings. (Sounds serious,  I’d better put the kettle on.)  The great conceit of this project has always been that if we somehow accurately  reproduce the original artifacts of the Orsova ballista and then design for them all of the ancillary components needed for a finished machine, and if we make and test the whole apparatus to encourage maximum performance;  then that result would be as near perfect an analog for the original machine as this researcher can muster. (phew! burnt my lip on that one.)

This approach respects the original Roman artifacts in two ways.    First,  our close adherence to the dimensions of the  parts dug out of the ground means that certain constraint dimensions will closely limit the size of the springs that will be allowable.  This will insure that the scale of our machine is in keeping with the original.  Second, by taking a ferocious interest in maximizing all issues related to performance, we can be confident our intent is exactly the same as the Roman engineers.   It’s a fair bet to suggest that there is probably no level of honorable* innovation that I can bring to this project that would not have been mirrored and bested by the Ancients.

Blend all that verbiage together and it follows that the most humble set of assumptions about how our finished machine should look and perform is to suggest an apparatus that is as mind bendingly kick-ass as possible.  We proceed accordingly.

A full scale poster of the original field frame is a useful binnacle for those days I get lost in the fog.   The old Vernier plate hanging to the right is one way to add on to the existing artifact and extract as much performance as possible from the whole field frame assembly;  e.g.  increased loads possible on the end caps to the field frames, fine gradation of torque on the spring bundles with a Vernier locking system for the washer.   There should be a variety of mumblings on Vernier plates and spring size  somewhere earlier in this tome.   While it is likely that the Romans used very stiff high collar bronze washers with the vernier hole pattern set into a thick  rim, for the moment our version  uses thinner forged steel washers combined with heavy Vernier plates because they offer more flexibility to change the design as desired.  The overall enhancement is pretty much the same with either construction approach, and so bears no violation to mar our conceits about authentic levels of performance.

(I had no idea one cup of tea could hold so much conceit.  Who knew I was supposed to tip it overboard?)

Graced by celebrity, our Adirondack never had it so good.

Poise is an art form difficult to master in these hectic modern times.    Daughter Sarah seems to be managing the fundamentals pretty well.   She reminds me that true beauty needs a  hint of  mystery to  deepen and flavor it.

All of Firefly’s components have been designed with the simple idea that they could be  manufactured by a competent blacksmith’s shop familiar with forging and casting.   My fifty odd years of experience in the metal trades tells me there is nothing in Firefly’s design that would not have been a  total snap for well funded and competent Roman armourers to manufacture.   The winch parts seen below have obviously been under the tender kisses of a modern CNC milling machine.  However, it is pretty obvious, the basic design could have been  knocked out by Roman metalworkers without much fuss.    Very AK-47.

Little did the barristas at Pioneer coffee realize that one of their signature , vente latte cups would soon be filled with Durham’s rock hard water putty, and be turned into a freaky mock-up for the starboard half of  an ancient Roman catapult winch.

No matter though.  Their coffee is brilliant.

Dual tapered drums, one of them modeled here  by the coffee cup,  will have to reel in a load that tops out at around 5,000 pounds.   It is a bit like pulling an increasingly reluctant eight ball down the table.   By the time it hits full draw, the ball is trying to run away from the winch with two and a half tons of hoopla under its belt.  …….Talk about sledge hammer breaks. …… Better not though, the Rebecca is not amused by cocky pool-shark types rampaging around on her new table.

Firefly’s winch is going to need to be stout.  4140 stout, I should think.  To make the effort of hand cranking as manageable as possible, the diameter of the  drum for our double action winch has to be chosen with the utmost care.  The taper on the drum is intended to increase the leverage available as the load gets stiffer towards the end of the draw.

At  full draw this particular size drum has a little room left on it for contingencies.  The rope seen here is a 5/8″,  low stretch Dacron,  with a breaking strength of 9,000 lbs.   The original Orsova ballista would likely have used sinew ropes on the winch.  Good luck on sourcing that these days.

It has become apparent that the universal joint for  Firefly’s stand will be better designed once we have established the exact center of gravity for the finished machine.  Hence the need to get the winch done first.

Now that the Honey-do list from hell has subsided a bit,  I can get back to work on all things catapult.  As for Firefly, the winch’s  the thing to catch the conscience of the King.