Bad sketches of war machines

[Gethuch]

I came up with these ages ago, when trying to think like a Fubarnii about the problem of transferring lethally large amounts of energy into your enemy's body very rapidly.

Basically, they both work like a tennis machine, but throwing rocks or shaped metal shot. The big flywheels let you take the power from a relatively small steam engine, and store it up slowly, then convert it to really fast motion of a projectile.

Witness my mastery of 'Paint' (!)






The calculations I used:
Iron is 7874 kg/m^3

Volume of a disc is 2.PI.r.t, where t is thickness



Mass of 1cm*1m (diameter) iron wheel is 247.37 kg.



For a circle, the moment of inertia is:

I=(m.r^2)/2



So the above wheel has



I=250*0.25/2=30.9 kg.m^2



The energy in a flywheel is (I.w^2)/2



(1 rev/sec=2PI rad/sec)



10 rev/sec -> energy=60994 Joules



Which will do 1KW for 1 minute.



50 rev/sec -> energy=1.5 MegaJoules

Which will do 25KW for 1 minute.

The rim would be doing 157m/s


200 rev/sec -> energy=24 MegaJoules (=5.2kg TNT)

Which will do 400KW for 1 minute.
The rim would be doing 628m/s

A 1kg projectile at 157m/s would have 25KJ of energy, taking 1/60 of the energy from the slower wheel, and equivalent to 48 9mm bullets, and almost double that of a 50-caliber "heavy" round.
Range ~= 2.5km (neglecting air resistance)

At 628m/s, it would have 400KJ, => 700*9mm or 26*50-cal.
Range ~= 40km! (neglecting air resistance)

I build a (very rough!) scale model of one of these, and it threw the scale-equivalent of a 2kg rock the scale-equivalent of 500m, which I thought was pretty good.

C'mon people, unleash your inner DaVinci! Sketch those crazy war-machines!

[Brandlin]

I'm sure the fubarnii engineers would have a great deal of fun in building such a machine ... right up until the point they have a point failure in one of the flywheels or its axle due to the stressed involved and all that energy is immediately and catastrophically released in many directions at the same time

You've left mechanical inefficiency out of your calculations too, which will take a fair chunk out of your energy numbers .

I do like the idea of alternate warmachine designs. I'm doubtful that the storage of energy in kinetic form is practical however. It takes an enormous amount of energy to keep the machine running and yet its only actually in "use" for those instants when you place ammunition between the discs.

Also you assume that Anyaral has the same universal constants as we do here on earth. There may be gravitaional differences...

I don't mean to nit pic or rain on your parade ... i like the idea of building stuff like this and dealing with the real problems of making them functional...

[Gethuch]

I'm sure the fubarnii engineers would have a great deal of fun in building such a machine ... right up until the point they have a point failure in one of the flywheels or its axle due to the stressed involved and all that energy is immediately and catastrophically released in many directions at the same time

Yeah, I think there was a sketch somewhere of the lowly Jenta, with his special stick, whose job it was to "fire" these things...

You've left mechanical inefficiency out of your calculations too, which will take a fair chunk out of your energy numbers .

I do like the idea of alternate warmachine designs. I'm doubtful that the storage of energy in kinetic form is practical however. It takes an enormous amount of energy to keep the machine running and yet its only actually in "use" for those instants when you place ammunition between the discs.

Back in the 40's they had buses powered by flywheels!
http://en.wikipedia.org/wiki/Gyrobus
Ok, so they had their problems, but it's not at all impractical. Decent bearings, and a polished flywheel surface can get the friction on them surprisingly low.

The axle can be very short, and very thick, unlike, say car axles.

I'll admit that catastrophic flywheel failures were among the more impressive explosions of the early industrial revolution. But that was mostly because they used stone for their flywheels. Besides, have you ever seen the catastrophic failure of a rocket? Weapons are dangerous!

Also you assume that Anyaral has the same universal constants as we do here on earth. There may be gravitaional differences...

Oops! Yeah, I did. Well spotted! I know it's pretty close to Earth's gravity, but I can't remember precisely.

[Brandlin]

i think one of the things that gets missed in conversations like this is the maturity of technologies.  For example, one of the things that held up the development of steam engines was that they couldn't make cylinders and pistons accurately enough to hold the steam. Earlyaccounts talk of inaccuracies of 1/4" and i've seen calculations suggesting some of these engines were 2-3% efficient. 97% of the energy wasted! It took decades for them to refine the production techniques to a point where they could do in the physical world what they could calculate on paper.

there is an assumption often in discussions about technological development in alternate worlds that because you CAN do something then its as good as we can do it NOW.

For example, we know that fubarnii have access to iron and can form it, and you are assuming that they can cast it into flywheels. Well ignoring the fact that a furnace hot enough to achieve that was a massive step in our technological development, lets say they are casting iron into sand casts. Iron of this sort is  notoriously fragile, it has very low toughness (resistance to impact and deformation) so would be highly likely to fracture and shatter rather than bend when put into a high stress environment.

The kind of technologies required to make such a disc out of a material with a higher toughness and therefore ability to absorb energy without fracturing would require knoweldge of steels rather than iron, requiring a host of chemical and metallurgical and production advances. In fact bronze might even be a better material as its a lot tougher than cast iron... but it is less dense so its a trade off (as is most engineering)

The second problem comes that if we say they hav these technologies then why d we not see them elsewhere? It would lack all internal consistency to suggest that some of these things can be seen in some areas rather than in others. I accept that there may be cultural issues as to why certain things don't change but I don't see much iron at all in the fubarnii culture... In fact if they have steam engines and the technology to make highly accurate contraptions like this with the relevent materials then i'm a little surprised they aren't chugging around the countryside in horseless carriages.

Yes, they had flywheel buses in the 40's. Most HGVs and buses still have them. In fact they are on most audi's these days... but they are not made out of fragile cast iron on fragile cast iron axles. The reason busses in the 40's had flywheels was that they stored energy from the bus going down hill or when the bus was idling at lights etc. its energy that was recovered that would otherwise be lost. What you are suggesting is a flywheel that is being constantly powered.

I'll reiterate - i'm not trying to nit pick or do down your suggestions. Nor am i saying its not possible. I really enjoy the debates about how society and technology might move forwards in a way that doesn't mimic that in our own history. But at the same time there are reasons that devices such as this were not in use through our history.

and yes i've seen many catastrophic failures of weapons on the test ground - remember what i do for a living

[Jubal]

Where would Fubarnii apply warmachine technology? As far as I know they've never needed siege warfare bar for bringing down Devanu towers ages ago (and single towers can be nicely destroyed with explosives and sapping; we can assume that the partially subterranean Fubarnii would make good sappers, too), and besides most of their cities are underground so our rock-lobbing stategies would become a littlesuperflous. War machines for taking down large foes would still be of use, but these would be in the light-artillery-with-relatively-short-range line, possibly baruk-mounted or on a swivel. Long range anti-personel weapons would be of little use as the Fubarnii can't see well enough to aim at a Devanu if it's a really long way away.

[Brandlin]

Very good point well made Jubal.

As i understand things the Devanu are hardly organised, they're more a feral, tribal threat, almost monsters. So the Fubarnii would have needed skirmishers and hunters and courage and organisation not large scale machines of destruction.

When it all kicks off between the empire and delgon though - that could be a different matter!

[TheGremlin]

Especially in tunnel fighting. It's a veritable mine of unexplored possibilities.

[Carcharoth]

Lots of interesting stuff...
There hasn't been much large scale Fubarnii vs Fubarnii conflict, but there have been some inter-clan conflicts over the normal things like territory. The Devanu can be viewed as a force of nature - they take enough effort to control that diverting military forces elsewhere is risky. Doesn't mean it hasn't happened though.
Knights do not get involved in those conflicts, and it is the Emperor's prerogative to withdraw the knights if any clans get too unruly. That has only happened a few times in history, and the results have generally bad enough that other clans generally tow the line.

Engineers do sometimes just build stuff though, even if they don't expect it to be useful. I expect some engineer successfully built a small version of Tom's device from wood  a little steam engine and a few 'rubber bands', and then started to wonder how big it could be made. That will have lead onto lots of different technical problems, which he may have consulted his various friends across the empire about. It just depends whether he bothered to sort them out, or if he got distracted first. Then again some of his friends may have taken his designs and run with them, using the excuse to try out their casting techniques, and boasting about how far they managed to throw some Delbur (similar to parsnips) with their new designs. It seems highly likely that some of the experiments didn't work out so well, but as long as they weren't fatal then that wouldn't be too much of a deterrent.

I generally imagine most inventions would follow that sort of chaotic development process...

[Gethuch]

For example, we know that fubarnii have access to iron and can form it, and you are assuming that they can cast it into flywheels. Well ignoring the fact that a furnace hot enough to achieve that was a massive step in our technological development, lets say they are casting iron into sand casts. Iron of this sort is  notoriously fragile, it has very low toughness (resistance to impact and deformation) so would be highly likely to fracture and shatter rather than bend when put into a high stress environment.

The kind of technologies required to make such a disc out of a material with a higher toughness and therefore ability to absorb energy without fracturing would require knoweldge of steels rather than iron, requiring a host of chemical and metallurgical and production advances. In fact bronze might even be a better material as its a lot tougher than cast iron... but it is less dense so its a trade off (as is most engineering)

They would indeed make both the wheel(s) and axle(s) out of steel - it said "iron" because I looked up the elemental density, and just cut-and-pasted that into my notes. D'oh!

The second problem comes that if we say they hav these technologies then why d we not see them elsewhere?

Because Mike hasn't sculpted them? He's happy (and probably sensible) making game-characters at the moment

It would lack all internal consistency to suggest that some of these things can be seen in some areas rather than in others. I accept that there may be cultural issues as to why certain things don't change but I don't see much iron at all in the fubarnii culture...

Yeah, someone made a comment early on about the Fubarnii not using much metal, and a whole thread ran with it before I spotted it and corrected it. It seems to have stuck, though.

In fact if they have steam engines and the technology to make highly accurate contraptions like this with the relevent materials then i'm a little surprised they aren't chugging around the countryside in horseless carriages.

The countryside, no. Their roads suck, and they haven't quite managed to organise an Empire road-building program. They're like the anti-Romans! They're great at inventing, but suck at organising.
They have motor-transport in some of the bigger cities, though. I seem to recall that Gar Loren has a railway...

Yes, they had flywheel buses in the 40's. Most HGVs and buses still have them. In fact they are on most audi's these days... but they are not made out of fragile cast iron on fragile cast iron axles. The reason busses in the 40's had flywheels was that they stored energy from the bus going down hill or when the bus was idling at lights etc. its energy that was recovered that would otherwise be lost.

No no! the gyrobus was powered by a flywheel. An electric motor span it up at busstops and the bus terminal, and it drove around town powered only by its flywheel. Up to 10km on one "charge", with charging taking between 30 seconds and 3 minutes.

What you are suggesting is a flywheel that is being constantly powered.

Of course, the application is slightly different. But the principle of slowly feeding power in, then drawing it off in short bursts is sound.

I'll reiterate - i'm not trying to nit pick or do down your suggestions. Nor am i saying its not possible. I really enjoy the debates about how society and technology might move forwards in a way that doesn't mimic that in our own history. But at the same time there are reasons that devices such as this were not in use through our history.

No worries   Although I do have a terrible temptation to get some plywood, and try to settle the disagreement the Fubarnii way - by building one!

[Gethuch]

Where would Fubarnii apply warmachine technology? As far as I know they've never needed siege warfare bar for bringing down Devanu towers ages ago (and single towers can be nicely destroyed with explosives and sapping; we can assume that the partially subterranean Fubarnii would make good sappers, too)

Hoo, yeah. The Devanu hate tunnels. Explosives were a surprisingly rare solution - they were extremely rare back then, and they're still not great now.

And yes, these were imagined as first attempts to make weapons for use against a massed foe - something not very common in the history of the Empire. They don't throw anything big enough for assaulting a castle, and they're not accurate enough to pick off a Devanu. But a steady rain of cobblestones would be very discouraging for an advancing army.

[Rick]

Well, I had this idea. It's a mechanical digger, but if you turn the belt round, crank it up a bit and feed in a steady stream of stones, you could get the effect you're looking for. I sort of imagine fubarnii artillery to be adapted from other devices or technologies.

[Rick]

Oh, meant to add that Gethuch's piccies made me think of some of the designs from Scrapheap challenge - didn't they have a coconut-flinger that worked like that?

[Gethuch]

Don't think I saw the coconut-flinging episode! They had a golfball-machinegun once, which worked in a similar way. They just got a moped or little motorbike, and used the rear wheel as the flywheel. Pressed another wheel up against it, revved it up to about 70MPH, and fed the golfballs in between. Very effective!