Traveller: The New Era Discussion on Traveller: The New Era 
October 27th, 2017, 08:39 AM


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I found data on a stone thrower loaded as part of a ship's equipment that listed the weight of the machine at 1820 kg and the size at firing 2.2 kg stones. This weight probably includes the ammo for it, since the data on the Marines included all of their equipment with their weight.
That is enough to confirm Campbell's 500:1 weight ratio over the 100:1 weight ratio from modern reconstructions. So I'll go ahead and update the weight calculations in the earlier post #3.

October 27th, 2017, 09:48 AM


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Quote:
Originally Posted by TheDark
Nick Watts made DuraEuropos style bolts to three scales. The smallest was 21.5" and 276 grams, the medium one 29.5" and 340 grams, and the largest 36" and 521 grams.

I ran some designs using bolts and found that the weight of the bolt is roughly equal to the weight of the stone.
For example, the 36" and 521 grams bolt is 0.914 meters and 0.546 kg.
From Vitruvius, the "washer hole" would be 0.914/9 = 0.102 meters diameter.
The "washer hole" for a 0.546 kg stone would be 0.106 meters diameter.
So the bolt throwers just use very small stone throwers, or the larger stone throwers just throw very large javelins.
Using Vitruvius' equations relating both stones and bolts to the "washer" diameter, we can calculate the length of Vitruvius' Bolt for any given weight as:
Length of Bolt = 1.169 x (Wa)^0.33 = Meters

October 27th, 2017, 07:03 PM

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One thing I noticed today going back through Watts' posts is that his ballista was getting close to 100 m/s of velocity with 422 gram bolts, which are fairly heavy for his machine. Changing that would require rejiggering a bunch of the formulas, so I'm not advocating for a change, just putting data out there for review.
However, I would like to discuss crew sizes, since Demetrius' 78kg stonethrowers apparently had a crew of only nine, although that was in a siege tower that may have had pulleys to provide them with mechanical advantage in drawing back the arms. Per steps 3, 6, and 7, a 78 kilogram stone will have 97,500 joules of energy, require strength 1625 and a crew of 233 to achieve Reload 5. It would need a crew of 47 to get Reload 25.
One solution might be extension, so a tenth of the crew has Reload 50 and a twentieth has Reload 75. I'd be OK with this, since it suggests a ~4 minute reload period for a heavy torsion engine (in fact, even that might be too fast).
The other option would be to drop crew sizes, though I don't know what they "should" be, since there's little information I've found on anything else except the smallest scorpios and the onager.
There should probably be a maximum crew based on some sort of reasonable measure, since 233 people working on a single siege engine, even if it's out in the open, seems improbable. And, on the flip side, doubling crew on small torsion pieces might reduce Reload to 3 or 4, since the light scorpios seems to fit into Crew 1 using the design sequence, but had 2 crew and fired 3 to 4 times per minute, which is faster than Reload 5.
Quote:
Originally Posted by timerover51

I have a dead tree edition of PayneGallwey. There are some accuracy issues here and there with him (his onager in particular; De Reffye's version is more likely to be correct). His ballista probably existed at an early development stage, but would have been dangerous to the artillerist  if the arms aren't equally torsioned (due to one skein getting damp or having a few strands snap), the bolt can jump the track. On an Orsovatype ballista, a jumper can keyhole through the large gap in the frame. On a Gallweytype ballista, the jumper can hit the large inner stanchions and become shrapnel ricocheting back into the artillerists' faces.
Quote:
Originally Posted by atpollard
I ran some designs using bolts and found that the weight of the bolt is roughly equal to the weight of the stone.
For example, the 36" and 521 grams bolt is 0.914 meters and 0.546 kg.
From Vitruvius, the "washer hole" would be 0.914/9 = 0.102 meters diameter.
The "washer hole" for a 0.546 kg stone would be 0.106 meters diameter.
So the bolt throwers just use very small stone throwers, or the larger stone throwers just throw very large javelins.
Using Vitruvius' equations relating both stones and bolts to the "washer" diameter, we can calculate the length of Vitruvius' Bolt for any given weight as:
Length of Bolt = 1.169 x (Wa)^0.33 = Meters

That's very useful to know, and makes the design sequence easier. I'm torn on how to handle the Dam/Pen relationship for bolts versus stones. They're low enough velocity that it feels like bolts should have better Pen (and maybe Rng?) but less Dam than stones from the same size machine. Or maybe they just scale up in Dam less, so that they're more efficient at the smaller size but become less effective at large sizes. I'm mostly brainstorming here without solutions, but it feels like there needs to be a reason the heavy machines are stonethrowers and not giant boltthrowers.

October 28th, 2017, 02:49 PM


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Crew size were just a W.A.G. based on the STR calculation for crossbows in WTH. It is more likely wrong than correct.
I would prefer to start with some real world or historic data and extrapolate from that, but I didn't find anything. One thought is that the crew needs to turn the machine to aim it and a typical man can lift 50kg repeatedly, so a minimum crew of 1 per 50 kg of total machine weight might make a good starting point.
What I really need is SOMETHING on historic rate of fire.

October 28th, 2017, 07:25 PM

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Quote:
Originally Posted by atpollard
Crew size were just a W.A.G. based on the STR calculation for crossbows in WTH. It is more likely wrong than correct.
I would prefer to start with some real world or historic data and extrapolate from that, but I didn't find anything. One thought is that the crew needs to turn the machine to aim it and a typical man can lift 50kg repeatedly, so a minimum crew of 1 per 50 kg of total machine weight might make a good starting point.

It would depend on purpose. For antipersonnel machines, certainly, that makes sense. A lot of siege artillery, though, was basically set up in place to pound one section of wall and had no real ability to reaim.
Quote:
What I really need is SOMETHING on historic rate of fire.

I'm not sure that anyone recorded that, so reenactors are the best shot we have.
Legion XXIV has achieved 3 rounds per minute with a scorpio (ignore their explanation of palintone, which is wrong, and cover your eyes at Legion VI's hideously misunderstood and inefficient engine). The Roman Iron Industry in Britain has a passage that states reproduction carroballistae have gotten up to 4 rounds per minute. Armies and Enemies of Imperial Rome suggests for onagers 1 round per minute for a 10 mina (4.37 kg) thrower, 1 per 5 minutes for a 30 mina (13.1 kg) thrower, and 1 per 10 minutes for a 1 talent (26.2 kg) thrower, but I don't know where they got those numbers from.

October 28th, 2017, 09:45 PM


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Quote:
Originally Posted by TheDark
It would depend on purpose. For antipersonnel machines, certainly, that makes sense. A lot of siege artillery, though, was basically set up in place to pound one section of wall and had no real ability to reaim.

I read about one of those recreation Ballista spear throwers placing 5 shots in a 3" circle at 50 meters and Archeological evidence of an actual Roman siege where a Ballista sniper placed 4 shots in a 3 meter circle at 130 meters.
So I think the Ballista needs a crew to reaim it after each shot since it seems too accurate for battering walls. For Trebuchet, I agree that crews to move it are not the best measure (although some sort of minimum crew to fire and optimum crew to turn might be useful).
Quote:
Originally Posted by TheDark
Legion XXIV has achieved 3 rounds per minute with a scorpio (ignore their explanation of palintone, which is wrong, and cover your eyes at Legion VI's hideously misunderstood and inefficient engine). The Roman Iron Industry in Britain has a passage that states reproduction carroballistae have gotten up to 4 rounds per minute. Armies and Enemies of Imperial Rome suggests for onagers 1 round per minute for a 10 mina (4.37 kg) thrower, 1 per 5 minutes for a 30 mina (13.1 kg) thrower, and 1 per 10 minutes for a 1 talent (26.2 kg) thrower, but I don't know where they got those numbers from.

Thanks.
I'll start with this data and see what I can come up with.

October 29th, 2017, 12:47 AM

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Quote:
Originally Posted by atpollard
I read about one of those recreation Ballista spear throwers placing 5 shots in a 3" circle at 50 meters and Archeological evidence of an actual Roman siege where a Ballista sniper placed 4 shots in a 3 meter circle at 130 meters.
So I think the Ballista needs a crew to reaim it after each shot since it seems too accurate for battering walls. For Trebuchet, I agree that crews to move it are not the best measure (although some sort of minimum crew to fire and optimum crew to turn might be useful).

Watts has gotten a 2" grouping at 50 yards with his Orsova replica. He's the only person aiming and firing it. The bottom of this post shows him firing it from the back of a pickup truck (it's too heavy for him to move without an overhead crane). It's a 300 yard shot leaving the ballista. He uses a shoulder brace to adjust the aim, with some sort of universal joint to allow elevation and rotation. There's no evidence I'm aware of that the Romans used a shoulder brace, but some sort of aiming lever seems like a device they (or the Greeks) would have developed.
One other possibility for ammunition would be sling glandes. There's been a bit of an argument over whether torsion engines were used to fire them. Nick's tested it, and his machine would fire packets of fourteen 31gram lead shot at around 300 fps. It would add something similar to grapeshot to the available types of ammunition.

May 6th, 2018, 04:35 PM

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I was reading a translation of Konstantin Nossov's work on ancient and medieval siege warfare, and one useful tidbit came up for torsion artillery, which is that the length of such a siege engine is double its span. It's a small thing to keep track of, but useful if one's trying to figure out how many engines can fit in a tower or on the deck of a ship.

January 26th, 2019, 12:04 AM

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Quote:
Originally Posted by atpollard
3. Energy (E) = Wa x 1250 = Joules
12. Muzzle Velocity (MV) = (2x E/Wa)^0.5 = m/s [typically 50 m/s]
13. Short Range (SR) = (E / Wa)^0.5 = Meters [typically 35 meters]

For fun, I decided to try to tweak the formulas to match Nick Watts' Firefly, which fires a 467 gram bolt and generates 1,150 footpounds of energy (~1,559 joules) with a muzzle velocity estimated at 360 feet per second (~110 m/s) and a maximum range of 845 yards (~770 meters). Doing so requires the following changes to the quoted formulas:
3. Energy (E) = Wa x 3250 = Joules
12. Muzzle Velocity (MV) = (2x E/Wa)^0.535 = m/s [typically 110 m/s]
13. Short Range (SR) = (E / Wa)^0.565  Meters [typically 96 meters]
I also personally use a divisor of 5 instead of 15 for nongunpowder projectiles (arrows, atlatls, etc) in the damage formula, since the existing formula from WTH didn't seem to adequately model bow damage (a bow that required STR 12 would do 1d6 damage, implying an English longbow is equivalent to a light pistol cartridge). Firefly is either a Dam 3 or Dam 8 weapon depending on which divisor is used.

January 26th, 2019, 12:40 AM


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Thanks for posting that! And the link, that was an interesting blog.
I did like the line, when talking about testing an earlier version, "After the 5" diameter, 32" long torsion springs were tuned, it would put ten shots into a 3 inch circle at 50 yards."
Yes, ballistaesnipers can ruin your whole day.

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