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.

One Response to “The 5,000 lb eight ball”


  1. Captn Harpoon says:

    hmmmm. My email seems to be missing some ranging stats with the new arm positioning. The new angles will cause the machine to draw somewhat different.

    Your average max draw length was approx. 50 inches. You will need more than that to utilize full draw weight or power.

    Assuming the winch is provide a direct pull no use of pulleys, than you will also have to consider the draw length and number of coils around the drum needed. This should dictate a minimum size and help with calculations.

    In studying all available stats on historically accurate builds, the inswinger models can rarely use full draw if the bundles are fairly tight. With the arms in what I consider the proper and accurate positioning, exploiting Fireflys true potential with a full 60 plus inches of draw is to be expected I would hope.

    Now to live up to my nickname here, I was wondering if you could further increase the size and length of your projectiles – at least one of them?

    I am convinced Firefly can chuck a 65 inch long spear tipped with one of your finely crafted points at a fairly good clip of around 285 to 325 fps provided weight does not exceed 15000 grains. The diameter of your string suggests a thickness of an inch and a half could be supported.

    Given Firefly at full draw is right about an est. 60 – 63 inch drawlength, a 65 inch “arrow” is not unreasonable. In any case, I think you need to bump the weight up to a minimum of 10,000 grains to use more available energy and keep arrow speeds within the material tolerances. With too heavy a weight or FOC, the acceleration might be to much resulting in grievous injuries or worse.

    Just my way of thinking. If something funky with the arrow or bolt does happen, its better to have it happen in front of the machine than behind it. The longer and much heavier arrow provides a certain degree or margin of safety.

    I will tell you with certainty that no crossbower would ever advise shooting a WOODEN arrow from any modern crossbow or compound bow. Firefly is already faster than many production crossbows on the market – a testament to your skills and craftsmanship.

    I love to get some stats/vids on any shooting sesssions if ya have em handy.

Leave a Reply