A new Roman arrow firing machine

[orcbow]

Dane- That is really cool. I want to make one too, but I don't have any knowledge of the metal working aspect. But for now I am working on other things.

[D. Tiller]

Thanks Dane! I think that small one you mentioned would be aw some to try to build. It seems to me they must have used smaller man portable machines for sniping purposes. Precursors to the crossbow?

I know the Greeks built a smaller version that you used your body weight to cock the Ballast with. I have to think there must have been a greater advantage to using these than a bow but don't know what it could be. Longer range? Better penetration? Able to carry more bolts than arrows?

Dane do you happen to know what animal the sinew came from for these weapons? I have a feeling that the modern machines I have seen built with Dacron are lacking in potential due to the artificial nature of the rope being used. Plus, there is a stretch and return factor with animal hair or sinew that you don't get with Dacron or other modern materials. I bet it reduced wear and tear on the engine and increased the distance and speed with which the bolts  would fly. Do you think this is possible Dane?

Question, do you think they used a ratcheting system with the small hand portable machine? I have a feeling it was more of a physical body effort with the smaller ones.

David T

[Dane]

Thanks, Orcbow. I started these projects with zero metal working skills. Like bow making, I wanted to learn, so I had to decide to learn the necessary metal skillls. They are pretty rudimentry, really. Casting is not impossibly hard to learn, and I made myself a small propane fired melting oven, basically a metal cylinder on end lined with refractory and using a commercial bbq tank with a high-volume regulator and hose so I can get the needed psi to get it to 1800 degrees. Hand made rivets are not that easy, but not too hard either, mostly using a heavy ball peen hammer carefully to flatten the shank ends, then peening the edges around and down onto the sheet metal. As for hand forged nails, my blacksmith friend is helping, though I want to learn to smith one day. I just picked up an antique anvil today, cheap! Found it in a dingy little antique store near me. More than large enough (I can barely lift it), and it is probaly American, German, or English made, so good quality.

Posted are two shots of my first ever bluing. This is to simulate the way actual sheet iron would have looked as done by the Romans. I used Vans bluing, easy and fun to use. The part you see is an inner spring frame stanchion. I am plating all the frame parts, and it will weight quite a bit more when it is done. One day, I want to builld one of these machiens using reproduction ancient Roman and Greek hand tools only, only using the same processes that would have existed 2000 year ago, such as chiseling out the various holes, no power drills, etc.

Dave, I appreciate the interest! The Greek belly bows, called gastrophetes, really are the first true catapults. If you look at that shot of me at the Vermont event, you can see the scorpio-minor (lesser or small scorpion) on the ground, the one I had been posting about a while back. It cocks by using your weight on the back horizontal brace, leaning forward to the slider is against the ground or a handy wall, say, and your weigh spans the machine. I am making it using the Greek style linear ratchets, you can see the SketchUp drawing I did a while back during the design phase. The advantage is that you can fire an arrow with a hand held machine that is much stronger than the strongest self or composite bows, and the trajectory is very flat, and so fast you literally can not see the bolt coming at you, unlike a bow. These things are supposed to be so powerful, they can defeat any known armor of the day, and easily punch through chain mail with heavy arrow tips, very similar to the medival bodkins. As well, it is much easier to train a man to use this than to use a war weight bow, as we all know. It took a life time to get proficient with a heavy war bow.

The gastrophetes used, we think, a composite bow, so it is similar looking to a cross bow, but much heavier, much earlier than even the first wimpy little cross bows.

As for sinew, that is the holy grail for modern catapult builders! You need so much sinew, no one has tried, until now. Even Dr. Schramm, one of the great early pioneers of bow reconstructing failed in this area. I dont yet know how much sinew would be needed for 150 feet of rope, what I will need for the 2" machine, let alone the amount for a large balista, which has huge springs. You are right, almost every single interpreted catapult has used dacron rope. It is not the best solution, but used frequently. Horse hair rope is a good second string material, though, and what I am using until I can acquire the amount of sinew I need for future projects. 

How Vetruvius described creating the rope springs is that the engineer build a special small winding mechanism, and then pluck the sinew rope at regular intervals, to determine that he has equal tension throughout the processes. All anyone knows now is that real sinew rope would be incredibly effective, and we can learn too the disadvantiges of using that materil in the field, such as during damp weather, things like that.

I doubt they used ratchets with the small machines. My thoughts are that about 1.5" and up for spring diameter, you need a winch system of some sort to span the machine. The gastropetes and my little machine will use body weight, and it simplfies construction considerably.

Dane



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[D. Tiller]

Are there any pictures or ancient diagrams or text describing the smaller ones?

[Dane]

Alas, no, only literary reference. They would certainly have followed the standard formulas developed by the Greeks and perfected by the Romans. I'll post that formula tomorrow; with it alone, you can design any machine you want based on desired spring size / arrow length, from a tiny dart to a 3' long mutant bolt of doom that would plow through the front ranks of the enemy and continue to travel along, it had so much energy.

The most valuable manuscripts we have were written by four engineers; Philon, Vitruvius, Heron of Alexandria, and Biton. The illustrations are often missing from some texts, and all are badly corrupted by copiest over the centuries, so much is still conjecture. Later, I'll post some, so you can see what I mean. They show all perspective at once, hard to describe, and worse to puzzle out.

If you are really serious about all this, you will find it as addictive in it's way as bow building. I have, anyway. And performance-wise, no bow of any kind, or crossbow for that matter, can come close to what these machines can do. Even the great English war bow seems tiny in comparision, as do the mighty asiatic composites. They dominated ancient battle fields for 1,000 years, so they must have been pretty good And another facinating thing about catapults is that they are the best documented and understood ancient machines.

[ThimoS]

I am as intrigued as I am lost.  What springs??? How does it work (in layman's tongue)

I like how you are fashioning it I just don't understand the mechanics.

[D. Tiller]

Torsion springs Thimo. Its like a bit bundle of sinew you stick a stick in and then twist up to store the energy. Then pull on the stick further to store more tension in it then let her go, WHAMO! Lot of torque to hurrel that thar bolt down range. One day I will definitely make one!

[orcbow]

I have recently watched a 6 part series called "Ancient Discoveries", that I got from the library. It was basically about the inventions of the classical world and how we should give them so much more credit for how advanced their technology and understanding of scientific principles was. Like the raw efficiency of the ballista's coiled rope springs. On the show, was even a reproduction of Heron of Alexandria's chain drive, repeating balista!

[Dane]

Thimo, how Tiller described it is prettty much it.

Here is a shot of a catapult over in England that shows the rope springs pretty well, and the arrow in place and ready to fire.

Bows are springs, as are rope bundles, just different kinds. With a bow, you already have energy stored in the machine, and when you pull it back to full draw, create more energy. To fire the bow, you release the string with your fingers, the bow arms move forward, and your arrow shoots toward the target. In a catapult, you have two very tightly coiled skeins of rope, held in place at top and bottom by metal washers and tenons, as you can see in the photo. You hammer two bow arms through the center of the rope springs, and impart ever more energy in the springs by twisting them and locking them in place with pins through the washers that go into the wooden spring frame. You winch back the bow string by using a pawl and a rope and winch system, lock it back with a trigger mechanism, put your arrow in place, and fire it by releaseing the trigger pawl. All that stored energy fires the arrow with so much force, it is impossible to see with the naked eye.

If you are the target and happen to be holding a shield, it shoots through that like it wasnt there. If you happen to be standing by a tree, the arrow has enough force to pin you through the spine to the tree, as did happen in one historic battle. One Latin name for these kinds of machines is tormenta, which is almost poetic



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[Dane]

I have recently watched a 6 part series called "Ancient Discoveries", that I got from the library. It was basically about the inventions of the classical world and how we should give them so much more credit for how advanced their technology and understanding of scientific principles was. Like the raw efficiency of the ballista's coiled rope springs. On the show, was even a reproduction of Heron of Alexandria's chain drive, repeating balista!

Orc, I saw that too. And the repeating machine that Alan Wilkins and Len Morgan build is pretty cool. The History Channel also had a show about ancient super ballistics that Alan demonstrated the machine on. Here are two shots of one, I believe in a museum in Germany (but not certain) that show it pretty well. Not sure if this is the same machine, or another reconstruction.

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[Dane]

Okay, I have both inner stanchions riveted and blued. Some additional filing is necessary to get a better fit, as well as touch up to the rivet heads, but overall, I am pleased. The next step is to cut out the plating for the outer stanchions, the band that goes around the two hole carriers, and then the counter plates for the washers, which will be inset into place.

Dane

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[D. Tiller]

Wasn't there some debat on how the arms where set up on these things?

[Dane]

David, there continues to be. As for my work, I debated with some other catapult builders (ballistarie in Latin) about how the arms are positioned. One school of thought is that the end of the arms has to slam into the inner stanchion back edges to absorb the energy as you discharge the weapon. I feel strongly that the inner arms don't do that, but possibly do hit the outer facing sides of the inner stanchions (why I plated them), but mostly, the bow string absorbs the energy, much like a bow does. Under no circumstances do you want the arms to slam into the outer stanchion recesses (the half moon looking cutouts). That is a good recipe for cracked stanchions and arms.

That is not even touching on the inswinger vs. outswinger debate that is currently pretty hot. I can try to fill you in on that, but for the purposes of an arrow firing scorpion, called a Euthytone, they are always outswingers.

Okay, here is the basic formulaa for calibrating a catapult. It is D = 1/9 L, D being diameter, L being length of arrow.

I am not sure if they decided on the arrow length first, or the spring diameter first, but my 2" machine, using that formula, has an 18" long arrow. 2" x 9 = 18". Or I could have formulated it by wanting an 18" arrow, and dividing by 9", which comes out to 2" for the spring diameter. All other dimensions for the arrow firing machines are taken from the spring size. A 3" machine would fire a 27" arrow, and a 4" machine would have a 36" long arrow.

If you want, David, I can email you a complete set of dimensions for all parts of the catapult. It is pretty long, and there are two, an earlier set of dimensions set out by Philon, and a later set developed by Vitruvius, an engineer who worked for J. Ceaser himself. I'm uising the earlier set, hence my machine being a Republic / early Empire machine.

Dane

[Dane]

Well, hi everyone. Here is the next installment. The spring frame is nearly done! I plated it with 16 gauge cold rolled steel, and it comes out to about 15 pounds now. I made homemade copper rivets, and getting a real anvil really helped there. One thing about working with steel is that no hardwood will feel as hard after that,

It was just slow but satisfying work. I used metal cutting saw blades with a regular power jig saw, and then lots of file work. I ended up painting all the metal work, as it would be almost a full time job keeping rust from forming on the plating, and I am pleased with how it turned out. I used brushed on metal primer, then hand painted the milk paint. The stuff is very easy to use, no fumes, but you have to be a bit cautious with it, as lime is an active ingredient, and it would not be good getting it in your eyes. I still have to put a finish on it, and am not sure what that will be yet. Probably spar varnish thinned with turpentine and then a beeswax coating over that.

Next step really is casting the bronze washers, and then making the rope. So, it is going relatively fast now. Fast is relative, as I am guessing the entire plating phase took 40 hours.

Attached are photos of the priming stage, and then a couple of the spring frame with red milk paint applied, about 3 coats so far. Any dings and such are actually okay, as this machine will represent a very old catapult that has been in Roman service for a long while out in Cyrenaica, which was a Roman province in North Africa. I am actually looking forward to how actual hard use will affect the machine. The frame really is like a little tank, it is so sturdy.

Dane

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[Dane]

Here is one more shot. Notice the two large nail heads on the ends of the hole carrier ends? Those were forged by Bob Patrick, and his work is just amazing. Catapults used a combination of nails and rivets to hold all the plating on the frames, so while I was not following an actual machine, I was following known practices in construction.

One of the most important things I was shooting for in this, my first ever sheet metal work, was good close fit to the wood, and clean lines. I think I did okay.

Dane

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