A Little Penatration... (testing a cheiroballista)

[Nerva]

Of course you're right. The problem is basically that the velocity of the projectile is just to slow, resulting in a very deep trajectory i.e. the degree of vertical deflection required quickly becomes unmanagable. Anything over 100m and your just hoping for good luck.

[Endre Fodstad]

Woooo...I love weapons testing. Done a bit of that myself, I have!

So when are you going to expose a real shield or armour to the cheiroballista?

something that struck me about that little test is just how effective a thin bit of plywood is against incoming missiles

Wait 'til you try "historical" plywood or solid shieldwoods...shields are impressive even against powerful projectiles.

[Matt Lukes]

Damn is that thing ever cool- I really want to make one of these myself some day and you've just given me that much more inspiration LOL :wink:

Any idea of the force with which that bolt hit? It might perhaps have toppled the person over?

That depends a lot on the weight of the projectile- it's pretty doubtful that this little bolt could knock someone over even if it were travelling extremely fast really... but it would certainly suck to get hit by LOL

[Matt Lukes]

something that struck me about that little test is just how effective a thin bit of plywood is against incoming missiles

it's always good fun shooting at things just to see what will happen. all in the name of research

Yup, I tried a bit of real 3-ply shield material (Birch) and was amazed at how effective it was vs. a sword thrust (more interestingly it actually 'captured' the point- withdrawl was very hard!) I would expect it to perform pretty well vs. bolts too at most any distance due in no small part to the increasing thickness of the wooden shaft.

[samuli seppanen]

I know this is an old thread, but I got to ask... how come the cheiroballistra is so underpowered even though it's has a very high draw weight (500+ lbs)? Of course the draw weight increases dramatically at the end along with the string angle, but still... A few bow/crossbow statistics as a comparison:

30 lbs all-wood, straight handbow: 39 m/s avg using a 26 gram arrow
50 lbs all-wood, straight handbow: 47 m/s ang using a 36 gram arrow
150 lbs crossbow with steel bow: 55,7 m/s avg using a 28 gram bolt, 47,7 m/s avg using a 50 gram bolt
300 lbs crossbow with steel bow: 54,4 m/s avg using a 52 gram bolt, 46,5 m/s avg using a 81 gram bolt

Any of these weapons (except the 30lbs bow perhaps) can easily punch through 9mm plywood or 1mm aluminum, depending on design of the arrow/bolthead. The bolts from both crossbows go through 2cm (soft) plywood and punch holes (but don't fully penetrate) 1mm soft steel plate. The boltheads are not designed for maximum penetration as they're pretty thick: 12x12mm (50 gram bolts) and 15x15mm (81 gram bolts) in diameter. Penetration could be easily doubled by using thinner and longer hardened steel heads - similar in shape to those you use on your cheiroballistra. Also, handbows used for war are generally of very high draw weight (100 lbs and up) and hence more powerful than the ones listed above.

Anyways, what I'm getting at is that current performance levels are clearly not good enough to warrant the complexity of construction and maintenance in Roman times. Have you managed to improve the results lately? Also, why not just use a chronograph to measure the initial velocity of the bolt? Cheap ones cost around 90 euros and give accurate readings _very_ easily. If you also measure the weight of the bolt, you can really start collecting hard data and start improving your cheiroballistra.

I hope all of this does not sound too negative but I felt somebody had to do a reality check. Besides this, I think your cheiroballistra is awesome, even if I disagree with some construction details.

[Gaius Julius Caesar]

The bolt that penetrated might just catch the bearer in the side of the head, so probably would be a killing shot.
Assuming he was keeping his head down from a shower of arrows as well....
How did I miss this thread... :?

[MARCvSVIBIvSMAvRINvS]

Great Cheiroballista !!!!

M.VIB.M.

[Crispvs]

A major problem that all of these tests suffer from (ours included) is that we do not have access to the sinew cord that the ancients preferred to use. The springing materials used in modern reconstructions are almost certainly seriously inferior to sinew. Although we have not actually done a properly measured test on Alan Wilkins' own cheirobalistra, which is sprung with horsehair, we have consistently got the impression in the past that it is more powerful than our own one which is sprung with nylon cord. If our impression is correct (and it does need to be tested), and if we are to believe that the ancients regarded horsehair springing to be poor in its performance compared to sinew, then even at high tension, our modern reconstructions cannot achieve anything comparable to the performance of the originals.

A few years ago a group of us were shown over Hod Hill in Dorset and were were shown the house where the majority of artillery boltheads had been found. It appeared that the artillery had been concentrated on this one house, probably as an act of intimidation. Most of the heads discovered outside the house were found in positions which suggested drift caused by a North East wind. The county archaeologist who showed us over the site said that based on the angle of entry into the chalk of the boltheads, they were most probably shot from the hill opposite, which he estimated at three to four hundred yards distant. Alan Wilkins has disputed this idea, saying that the scorpios would not have been able to achieve that range and has suggested instead that the cataplts were dragged up onto the actual rampart of the hill fort and oeprated from there. However, having been there and walked over the ground myself, I find it hard to believe (quite aside from the evidence of the entry angles of the heads) that they could have hauled their machines up there and got them working in a time which was less than the time it would have taken soldiers unencumbered by artillery to climb up the same distance and cove the ground to the house in any case, even if there were other houses in the way. Obviously there would have been defenders but Vespasian was no fool and I am sure if he intended to storm the hill fort he would have nsured he had sufficient numbers of men to do so. What would be the point therefore in hauling your artillery up to the rampart if your infantry could have got to the house already?
In the alternative scenario, with the artillery on the hill opposite, Vespasian has presumably ordered the artillery to target that house (which was the biggest and which was surrounded by an enclosure) as a demonstration of the power of Roman arms and to encourage the Britons to surrender and open their gates to the Romans. This would mean that they could achieve reasonable accuracy over a distance of 300+ yards.
Of course, if Alan is right about the range of the machines this could not be the case. However, if Alan's estimate of the effective range of bolt artillery is based on the tests we conducted a few years ago using our machine then we must suspect that had we been using sinew springing our testing would have demonstrated much greater ranges.

I too have heard the straining and creaking at high tension that Nerva described and it really is quite frightening. However, part of the reason for this creaking must be that the springing material has reached close to the limit of its elasticity and that therefore it is beginning to try to twist the wood of the machine as it has no more twist of its own to give. If the springing material had greater elasticity it could twist further and thus create more tension before it reached it limit, meaning that far greater performance could be achieved well before any of the creaking sounds started to set in.

Crispvs

[Warhammer1]

Samuli,

the easiest answer to your inquiry is simply that the machine component proportions are out of balance, so that any meaningul velocities cannot be had. Most notable the axle to axle spacing (to short) and the length of the limbs in regard to axle spacing AND spring size and length(too long).

there are two components to the acceleration vertical and horizontal, with way too much vertical movement happening. If you take a string and hold it by both ends, which will be the faster of the two - one where both hands draw the string directly away from you in a single direction(vertical) , or the test where you simply move the two ends of the string away from each other in opposite directions?

The vertical only movement will result in a projectile speed equal to the speed of the hands holding the ends of the string, and the horizontal only movement where by the strings speed is automatically doubled. both are unidirectional but one is definitely faster. this machine has an unbalanced movement. If both vertical and horizontal movement were equal, then the movement would be balanced. Thusly one may either retard or advance the machines velocity potential (amount of torque not withstanding) simply by adding to or taking away from the horizontal movement component. The above machine has a definite heavier vertical movement component than horizontal. Wider axle spacing will fix that, and so would shorter limbs.

Also, If you look closer at the pic a strand of rope appears to have broken or come loose on one side and that one stanchion or stop appears to be slightly torqued out of shape (bent inwardly). My eyes are not what they used to be so the bend part may not be correct.

I have a friend who has an awesome ballista, and I am slowly getting him to try a few of my outlandish ideas. One resulting in an immediate 22% increase. You will no doubt find his blog very interesting, so heres a link where I posted some of my inswinger research data. I would eventually like to get his machine up to 450 fps (with a 9-10 thousand grain bolt) which I believe is required to perform the kind of super performance historical accounts claim regarding range, accuracy, and power.

My research shows his machine may be the most advanced torsion ballista currently on the planet and if not, certainly one of the fastest. I cannot stand that Scorpyd crossbow RDT 165 is faster than Nicks machine. 450 fps or bust! http://wattsunique.com/blog/?p=3568#comments .

W.

[rocktupac]

Unfortunately there's only one way to find out for sure and I'm not trying that one

Come on! Why not? I was hit with an arrow from about 3m away while wearing my linothorax and survived

You can do it! :twisted:

[P. Clodius Secundus]

While I agree that using nylon rather than sinew rope casts doubt upon most modern results, I fear the the real problems with this size/model of cheiroballistra are more deeply rooted. The best results I've seen come from Alan Wilkin's own tests of his machine using horse hair rope. He reported impressive consistency at just over 200m. If you add to this result an extra 40% increase in power potentially available by switching it from out-swinger to an in-swinger(As reported by Aitor when he converted his smaller handheld version), you begin to approach the historical ranges. Add perhaps another 10% for sinew and you are throwing the same bolt 300m. Now add another 10mm diameter to the washers (AFAIK none smaller than 54mm can be directly assiciated with iron frames) and you get even more power that translates into some increased combination of speed, range, and/or projectile mass. It could be that the reason we haven't found any 45mm iron framers is that at that scale they just don't pack enough punch to justify the expense (think of the 37mm AT guns in WWII). Nick Watts is racking up some astounding numbers with his Orsova-sized weapon, but his innovative methods for stretching the bundles etc. may be skewing the results. If anyone has hard data for other large Iron-frames like Carnifex or Taurus Magnus they may be more instructive.

[Warhammer1]

There is a video on youtube "Mail Call" with gunny witha simular looking machine as this one except the size of Nicks machine (arms not included). It looks most like the Romania Orsova machine but for the life of me cannot figure out why they chose to make it an outswinger. I dont think it would make bolts fly any farther than this smaller one although it has 1300 lbs pull.

Perhaps it is the fault of the museum for displaying the frame and Kam incorrectly thus giving folks a corrupted perspective. The Kam is back to front and one spring frame is backwards.

Assembled correctly the longer tangs on the kam create an off-set for the stanchions giving the machine an extra 15-20 degrees of rotation set up as an inswinger. The significance is that (a) at 90 or even 100 degrees of rotation, the arms do not hit the "slack point" as Wilkins(?)stated happens. The machine is designed to use structural compression from twisting under load. There is a real reason for the tangs being staggered unless you make the kam so stiff it has no flex at all.

(b) The extra rotation means that the machine can be operated for much longer between tightenings provided both half springs pull in balance. When loosened some total rotation may be up to 130 - 135. More potential energy equals more potential velocity.

© As the ropes loosen with use, you may still collect max. pull by using a few extra degrees of rotation (has plenty more). A bonus is you get to utilize/expend a greater percentage of the machines available energy. More shooting time, less downtime, maximizing downtime for maintainance or tightening.

(d) blah blah blah and so on. I talk too much.Sorry.