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I want to explore an advanced Native American civilisation; assume their general 'technology level' is 'equivalent' to 13th-century Europe. Biggest difference is that their metallurgy is lagging behind; this country is only just starting to make use of iron for instruments larger than tuning forks, and they haven't invented any kind of steel yet. Other than that they're as advanced as you would expect: they have universities, an expansive bureaucracy, a long literary tradition, and lots and lots of warfare.

The important thing is that they got their civilisation to such heights without any contact with the Old World whatsoever. Because of this lack of cross-pollination up until the time of their discovery of the Old World, I have vested interest in making this culture 'strange' from the European perspective, including their solutions to known problems. Convergent evolution is a thing, but I do not want to rely on that to such an extent that any American tech I describe sounds like an Old World thing with a paint job.

So I want an original siege engine. Assume that, for much the same reasons as Old World states did, this civilisation too began to use stone fortifications and eventually fortresses. To deal with those, Old World engineers have developed many, many ways to sling projectiles either against those walls at great speed, or over the walls and onto the weaker buildings inside. That's what catapults, trebuchets and ballistae are. My idea is a giant atlatl or spear-thrower; to be realised as effectively a combination of a catapult and a ballista.

atlatl

Imagine this mechanism, but instead of a human arm you have the arm of a catapult.

catapult

The question: could this be a good alternative siege engine? I am considering two things:

  • Would it be suitable: is this instrument effective as I described it?
  • Would it be sensible: does it exist in a local optimum? I am kinda worried that any clever engineer would naturally decide to swap out the spear projectile with a ball and thus make it a regular catapult. But I am not sure of this: a giant arrow as a projectile is easier to aim, and in real life, ballistae only fell out of use with the fall of the Roman Empire.

If necessary, maybe the inefficient metallurgy could play a role in keeping the giant atlatl a viable machine, effectively preventing it from turning into a catapult? As said my interest is in keeping this civilisation weird.

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  • $\begingroup$ You are describing a bolt ballista with more moving parts. Most likely they would use a regular bolt ballista. $\endgroup$ – The Square-Cube Law Oct 8 at 7:07
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    $\begingroup$ @Renan Yes, assuming they have ever invented a bolt ballista. That's a different branch of weaponry, even if it launches similar projectiles, and I am fine with basically preventing that branch from existing for the culture in question, by simply saying that they had never thought of the thing (not every Old World culture invented ballistae after all). I am more concerned about any alternative designs that are so close to this mega-atlatl design that one would logically evolve into the other rapidly, like the standard catapult. $\endgroup$ – KeizerHarm Oct 8 at 7:16
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    $\begingroup$ iam not sure my self to make an answer but i believe it will be take alot of time to load the pole, assuming the spear also up scaled it probably a pole trunk size and iam not sure about the balance either, and i doubt it can fly far compare to balista and even mangonel so probably not positioned in safe distance against enemy range attack, and if you mean to put lots of normal size spear instead....that probably will fly chaotically and probably not in correct position. $\endgroup$ – Li Jun Oct 8 at 11:58
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    $\begingroup$ regarding logistic, honestly i think its not really an issue, carpenter can just carve or smooth it, and it can be carry in wagon just like other siege engine that is made in spot during siege, which majority is made of big wooden trunk and plank. $\endgroup$ – Li Jun Oct 8 at 12:03
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    $\begingroup$ For reference, the actual torsion field artillery piece used by the Romans to throw pointy things (apparently with great force and precision) was the scorpion. Here is one hobbyist detailed documentation. $\endgroup$ – AlexP Oct 8 at 13:32
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Not in the way you are thinking.

People already have made "upscaled atlatls"; they're called catapults and trebuchets. They just didn't load them with javelins, for several reasons.

  1. As @L.Dutch-ReinstateMonica already mentioned, logistics for the ammunition would be an issue. Like it or not, those javelins would have to be pre-made and then carted to wherever you want to use the atlatl. It's not a huge problem, but it is appreciable.

  2. They would be supremely inaccurate. Having used atlatls before, I can tell you from experience that using them requires many small adjustments during the swing, as otherwise the javelin will go flying off in the wrong direction. Having also used catapults, I can also tell you that you simply cannot get that level of fine control with a catapult.

  3. Even if you could make it accurate, it wouldn't be effective. The atlatl is an antipersonnel weapon. The ancient equivalent of a hand-cannon, to be sure, but still an anti-personnel weapon. Even scaled up, it wouldn't have the impact force to deal significant damage against the ten-foot-thick walls common in that era. Medieval militaries, recognizing this, loaded their atlatls with rocks. You could conceivably use it like a ballista, but it would be cheaper to just get a few ballistæ in the first place.

EDIT: To clarify my third point, a javelin of the same weight as a rock is going to do more or less the same amount of damage, but it takes a much bigger catapult to fire the javelin than it does the rock.

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  • $\begingroup$ Good answer, but regarding your third point: why is using a catapult to lob rocks more effective than using the same catapult to lob spears? It seems to me that the spear would be larger and have more mass than the stones. $\endgroup$ – KeizerHarm Oct 8 at 11:40
  • $\begingroup$ @KeizerHarm Have you ever heard of the Box Lifting Problem? It's an old math question which math teachers used to use to teach their students to check whether or not their answers are realistic. The problem usually is phrased something like this: "Somewhere in the world, there is a 3ft by 3ft by 3ft cube, which weighs 3 tons. How many people would it take to lift it?" Most kids will give the "right" answer, not thinking to check if you can actually get that many hands on the box. $\endgroup$ – The Daleks Oct 8 at 13:09
  • $\begingroup$ (cont'd) Your "super-atlatl" has a similar problem. You could use a catapult to launch javelins, but the javelin's un-ergonomic length means that you would have to use a bigger catapult than is needed to launch a similarly-weighted rock. $\endgroup$ – The Daleks Oct 8 at 13:14
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    $\begingroup$ @KeizerHarm I wasn't trying to compare you with a schoolchild, nor was I questioning your mental maturity in any way. As a general rule, I try not to use metaphors. I included the rock-lifting problem to provide background to my explanation of the problem with the super-atlatl. $\endgroup$ – The Daleks Oct 8 at 14:04
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    $\begingroup$ It came over to me like you were placing me in the position of those who don't understand why the 3-ton-cube cannot be lifted by people. In either case, it's a good answer overall, and I don't think I can do much better than someone who has actually used an atlatl. I suppose I'll have to look in other areas if I want to have original siege weaponry. $\endgroup$ – KeizerHarm Oct 8 at 14:25
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It Would be Very Hard

Atlatl's store energy in the javelin itself. The heavy stone/iron point resists motion more than the wooden shaft, since objects at rest tend to stay at rest.

This results in compression of the javelin shaft like a spring. When the Atlatl leaves the launcher, it un-compresses rapidly, pushing forward.

You can see this in the bowing of the javelin if you watch a slow motion video of an atlatl.

Atlatl actually tend to be made of soft wood, because hardwood doesn't flex enough.

To make a very large scale atlatl would be... interesting - you'd basically strip a pine tree, attack a big rock at the front, and then push it really hard from the back.

Maybe an H Frame could Work

Basically, we're building a giant slingshot, but we use a dart instead of a pebble, and counterweights instead of rubber bands.

Build a large scaffold shaped like a capital H. The atlatl sits with the back end on the ground, and the heavy end on the horizontal centerbar. Pulleys at centerbar height ensure that when the counterweights drop, the force on the javelin is applied at the rear, with the line of motion through the point.

We need the motion to be in line with the javelin in order to create the bending, which stores the energy from the counterweights for an explosive release.

Problems

The atlatl isn't cheap! The length, springiness, weight, etc are all important to getting the bowing right, and after you've invested all the time and energy in finding / cutting / tuning your javelin, you only get to use it once. This is the basic reason why bows are better for warfare than atlatls.

The too little force, and the atlatl doesn't fly right. Too much force, and the pine tree explodes in the middle of your army, and then doesn't fly right.

The pulleys - It's a non-trivial engineering challenge to transfer the force from the falling counterweights to the log / tree / atlatl.

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The main issue I see is that, while making a spear is not that resource intensive, making an upscaled spear to fit an upscaled atlatl would require much more resources, on top of those needed to build the atlatl.

Consider that carrying along all the ammunition is a burden on logistic: while a catapult can be loaded with materials found on the spot (stones, boulders, bricks), saving effort in transporting them, making a large set of upscaled spears require having decent trees around with straight and well balanced trunks, and not just any tree. That would imply taking along the ammunition.

From a pragmatic approach I think a catapult would still be preferred.

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  • $\begingroup$ Interestingly, Wikipedia does say that real-life ballistae were not transported in whole; only the parts not made of wood. The device was constructed locally, with its other components carved out of the local wood. That's an advantage of it being a siege weapon specifically; sieges already take weeks, so taking a day or two to construct the weapons won't cost you too much time. If the beams of a ballista could be made of readily accessible wood, couldn't spears be made of any wood as well? $\endgroup$ – KeizerHarm Oct 8 at 7:11
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    $\begingroup$ @KeizerHarm the problem with a spear is that you want it to fly straight, so it has to be straight and well balanced. That requires a well grown tree, not any random tree. More or less like it was for ship masts. $\endgroup$ – L.Dutch - Reinstate Monica Oct 8 at 7:27
  • $\begingroup$ Alright, thank you for the answer. I am not convinced that the necessity of bringing along some cartload of spears (which can have standardised dimensions and be produced en masse much like javelins and arrows) would be a fatal blow to this design, but it is a good thing to keep in mind. One could imagine that this device would first launch spears (because of their accuracy), and then be loaded with rocks and debris when the besiegers have ran out of them. Could be an interesting scenario where the civilisation sees European catapults launching nothing but rocks and assume we're all destitute. $\endgroup$ – KeizerHarm Oct 8 at 7:48
  • $\begingroup$ @KeizerHarm Regarding the idea that you could make the spears out of any wood you had on hand, I don't think so. Various types of wood are significantly different in terms of weight, strength, flex, etx. That isn't too much of a problem in a spear thrown by hand because you aren't going to throw it hard enough to break it, but with a large siege weapon the forces get pretty extreme. If you use the wrong kind of wood or a piece of wood with weaknesses like knots it could shatter before it even got in the air. The answer to the logistics question really depends on the scale of the weapon $\endgroup$ – Kevin Wells Oct 8 at 22:47
  • $\begingroup$ To clarify what I mean by depending on scale is basically that it is very easy to produce a bunch of spears if they are around the size of a spear you would use by hand, but if you want a large siege weapon that is capable of assaulting fortifications you probably need to be launching very large, very heavy bolts (think medium tree size). If you are using this weapon for many shots or if you have many of the weapons then it really will become a logistical problem $\endgroup$ – Kevin Wells Oct 8 at 22:49

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