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Author Topic: Steam Crossbow 101  (Read 11205 times)
The Emblasochist
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United States United States


« on: January 19, 2009, 04:58:07 am »

Hello ladies and gentlemen.  It seems that I have stumbled upon this bit of the aether by coincidence.  You see, I am in a state of quandary.  I am seeking to build a steam-powered crossbow, and it seems that the excellent people here might be able to give me some tips in how to create such a device. 

The basic design of the contraption is meant to be a drum or belt-fed crossbow that, when the trigger is pulled, a dart is fired from the chamber, and the feed device is moved into position for another dart to be fired again.  The whole device would preferably be working when completed, and the expectation is that use of the device is limited to about 5-10 darts before reloaded with water and darts.  If at all possible, I would prefer for the weapon to be self-contained rather than powered by an external water tank and coal heater, because it is meant to be only a piece of a steam-punk outfit. 

Any suggestions would be vastly appreciated!
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HAC
Steam Theologian
Zeppelin Overlord
*******
Canada Canada


HAC_N800
« Reply #1 on: January 19, 2009, 05:40:01 am »

If you're planning a prop weapon that is non-functional, then its merely a matter of making it look what you think it SHOULD look like..

If you are planning a functional steam device, then I'm afraid the biggest problems you have with your design spec are the laws of thermodynamics, and the engineering realities of steam power. To even begin to work out a steam power design, you need to calculate the pressures and volumes of steam needed, and then work down towards your physical and material design. Steam of suffciently high pressure to drive a projectile, will NOT come from a small steam plant. It takes a LOT of energy to generate HP steam.  The mechaincal aspects of handling HP steam are neither  simple, nor small.. There's a very good reason steam powered weapons were not sucessful as working designs (save for the Holmman Projector used aboard trawlers in WWII, but that had the ships boilers to help it along..

Heck, if its a prop, you could make it look suitably steamy very easily. 

Cheers
Harold
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The Emblasochist
Deck Hand
*
United States United States


« Reply #2 on: January 19, 2009, 06:05:50 am »

The design is meant to be fully functional, but at the moment, steam is not my only choice in terms of dart propellant, although it would fit the character's design much better had the crossbow been steam-powered.  Making it LOOK steam-powered is not out of the question, as long as the cost to fit the weapon with steam-powered looking design does not vastly increase the cost of making the device.  I wouldn't mind building one that is even a single shot steam-powered design later on, when money is less of a concern, but the first one is meant to be fully functional, no matter the means to do so.  Keep in mind that I am not expecting this thing to be semi- or fully-automatic, but rather single shot.
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HAC
Steam Theologian
Zeppelin Overlord
*******
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HAC_N800
« Reply #3 on: January 19, 2009, 06:37:21 am »

Let me put it simply... Steam is not an option here, not in a  handheld or portable design .  As I said, there's a reason there were no really sucessful steam powered weapons.
To begin with, steam power is not simple.As an example, you'd need to calculate such things as boiler hoop stress, which is only one of the variables to be taken into consderation in boiler design ,as well as  consider such things as thernal shock when injecting new feedwater after steam is used (I won't even begin to get into injector design, or firebox design and energy density of varying fuel mixtures, nor time-to-pressure relationships (ie how "free steaming" a boiler is)). 
  Steam power does not scale DOWN well. In steam, bigger is easier, albeit not cheaper.
Look at it this way, paintball guns work on the same principle of rapid gas expansion, BUT the gas is not generated at the weapon. It takes a fair bit of work to pressurize those cylinders. Steam is worse, because it requries a  state change from liquid to gas. Steam takes a lot of energy to porduce even at relatively low working pressure. Its not just a matter of boiling water. you need a lot more energy to take water at the boiling point and turn it into steam, which is a true state change. What you see coming out of a kettle is not steam.

That's my .02, based on a fair bit of steam power experience..

Cheers
Harold
 
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The Emblasochist
Deck Hand
*
United States United States


« Reply #4 on: January 19, 2009, 06:57:08 am »

I've taken more than just a rudimentary chemistry and physics class.  I am aware that steam isn't viable in a lot of systems.  But it IS a Victorian power source, and that's the reason that I was looking to make it at least look as though it was steam-powered.  The character is supposed to be a forest ranger that has come in contact with enough people from a Victorian 21st century, and through saving the lives of enough people of influence and science, has been thanked with the device in question.  Since I need to come up with another propulsion method, I would be willing to make it look as though it came from such a person as a steam fanatic. 
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akumabito
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« Reply #5 on: January 19, 2009, 05:29:26 pm »

I've taken more than just a rudimentary chemistry and physics class.

And HAC has decades of practical, professional experience with steam systems.
You'd do well to pay attention when he's explaining about anything steam related. Wink  




I am aware that steam isn't viable in a lot of systems.

Right. Then what makes you think it works in this instance?


But it IS a Victorian power source, and that's the reason that I was looking to make it at least look as though it was steam-powered.

Electricity, pneumatics, hydraulics and the internal combustion engine were all either invented or improved during the Victorian era.. I understand the 'cool factor' of steam, but as HAC said, there is a reason it has never been used for efficient weaponry.. considering your backstory of a person who is mainly concerned with high-mobility, steam would be opretty much down at the bottom of the list of possible power sources.
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Wayland2002
Snr. Officer
****
United Kingdom United Kingdom


« Reply #6 on: January 19, 2009, 05:33:54 pm »

Hello ladies and gentlemen.  It seems that I have stumbled upon this bit of the aether by coincidence.  You see, I am in a state of quandary.  I am seeking to build a steam-powered crossbow, and it seems that the excellent people here might be able to give me some tips in how to create such a device. 

The basic design of the contraption is meant to be a drum or belt-fed crossbow that, when the trigger is pulled, a dart is fired from the chamber, and the feed device is moved into position for another dart to be fired again.  The whole device would preferably be working when completed, and the expectation is that use of the device is limited to about 5-10 darts before reloaded with water and darts.  If at all possible, I would prefer for the weapon to be self-contained rather than powered by an external water tank and coal heater, because it is meant to be only a piece of a steam-punk outfit. 

Any suggestions would be vastly appreciated!

So is this actually a crossbow or a steampowered canon that fires arrows?
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The Emblasochist
Deck Hand
*
United States United States


« Reply #7 on: January 19, 2009, 08:13:56 pm »

The crossbow is supposed to be small enough to be used with one hand operating the trigger and one hand up near the front of the thing for stability while shooting, so I think of it as a crossbow.  I am not sure I understand what a steam cannon would be. 

I've taken more than just a rudimentary chemistry and physics class.

And HAC has decades of practical, professional experience with steam systems.
You'd do well to pay attention when he's explaining about anything steam related. Wink

Its not that I'm dismissing him.  I have no idea how much he knows about steam, and while it seems he knows worlds more than me about steam, it seems that you could work on being less condescending.

I am aware that steam isn't viable in a lot of systems.

Right. Then what makes you think it works in this instance?

I guess you've heard of hope.   

But it IS a Victorian power source, and that's the reason that I was looking to make it at least look as though it was steam-powered.

Electricity, pneumatics, hydraulics and the internal combustion engine were all either invented or improved during the Victorian era.. I understand the 'cool factor' of steam, but as HAC said, there is a reason it has never been used for efficient weaponry.. considering your backstory of a person who is mainly concerned with high-mobility, steam would be pretty much down at the bottom of the list of possible power sources.

And I suppose it's called STEAMPUNK because the emphasis ISN'T supposed to be on steam-power.  And I don't remember saying that the character was concerned about mobility at all.  Now, I do remember saying that "since I need to come up with another propulsion method, I would be willing to make it look as though it came from such a person as a steam fanatic."  But it seems that you just wanted to rip my head off.
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Prof. Albrecht Von Taggërt
Zeppelin Captain
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United States United States


Bettering mankind through science and engineering!


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« Reply #8 on: January 19, 2009, 08:25:43 pm »

Anything is possible with the right amount of imagination. Suspension of disbelief is where the trick is. Steam powered xbow, sure, functional with anything smaller than a hand cart sized steam engine, probably not. You could use compressed gas like the airsoft guns use. Is this to fire REAL bolts? I only ask because you get stopped with that thing and well your in a ton of trouble. None the less, look into how airsoft guns work, might be a viable source then jsut make it LOOK like it's steam powered with smoke makers etc.

Oh and this is a steam cannon:
Spoiler (click to show/hide)
It will have a steam power plant backpack just to run the A/C generator. So that gives you a idea. Mine is all looks tho.
Best of luck =D
« Last Edit: January 19, 2009, 08:28:00 pm by Prof. Albrecht Von Taggërt » Logged

akumabito
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« Reply #9 on: January 19, 2009, 08:35:19 pm »

I've taken more than just a rudimentary chemistry and physics class.

And HAC has decades of practical, professional experience with steam systems.
You'd do well to pay attention when he's explaining about anything steam related. Wink

Its not that I'm dismissing him.  I have no idea how much he knows about steam, and while it seems he knows worlds more than me about steam, it seems that you could work on being less condescending.

Hey, it was YOU who started asking about steam, and if you're even halfway serious about the subject you'll pay close attention to what he's saying. If you had bothered to browse the forum for a few minutes first, you had known Harold is our resident expert, and you'd also have known the usual answer to the many "I want to make a steampowered [insert object here]. Seems like you didn't bother getting to know the forum OR research the subject, and you're offended by me being condescending? Hell yeah I'm being condescending, and rightfully so Tongue   

I am aware that steam isn't viable in a lot of systems.

Right. Then what makes you think it works in this instance?

I guess you've heard of hope.

..hope based on what? You haven't shown the tiniest bit of understanding about anything steam related, and you seem perfectly ok ignoring the advice you're being given.    

But it IS a Victorian power source, and that's the reason that I was looking to make it at least look as though it was steam-powered.

Electricity, pneumatics, hydraulics and the internal combustion engine were all either invented or improved during the Victorian era.. I understand the 'cool factor' of steam, but as HAC said, there is a reason it has never been used for efficient weaponry.. considering your backstory of a person who is mainly concerned with high-mobility, steam would be pretty much down at the bottom of the list of possible power sources.

And I suppose it's called STEAMPUNK because the emphasis ISN'T supposed to be on steam-power.  And I don't remember saying that the character was concerned about mobility at all.  Now, I do remember saying that "since I need to come up with another propulsion method, I would be willing to make it look as though it came from such a person as a steam fanatic."  But it seems that you just wanted to rip my head off.

There is a big difference between fact and fiction, young paddawan. Hence the earlier suggestion you make a non-functional prop that only appears to be steam powered.

About your character not being concerned about mobility; what kind of ranger will haul several hundred pounds of furnace/boiler and associated machinery on his trips?

..oh, and I'm being nice today, so no complaining about my manners please Tongue





Anyhow.. welcome aboard mate. I'm sorry 'bout the whole "Steam Power Reality Check", but it is a necessity I'm afraid. As much as we all love historic steam engines and their appearance in fiction, real life is rather unforgiving with mishaps and the like, and we'd rather not have any forum members blow themselves up or having their flesh stripped away by a jet of high pressure steam you see..
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The Emblasochist
Deck Hand
*
United States United States


« Reply #10 on: January 19, 2009, 09:14:42 pm »

Actually, I did read the forums and saw that HAC is quite versed in steam-powered stuff.  I'll admit that I didn't research the steam-powered viability of my device, but it only came up as a means when a friend on the boards here suggested that it might be possible.  Also, I might repeat myself, but I did say that since its not even theoretically possible, I'm looking for ideas about how to make it look that way... But, the kind of ranger that would carry such a gargantuan load is the one that's been saved a couple times with it when facing beasts that won't go down from a human-powered bow and arrow.  This is the last resort weapon, like I said, but it IS quite effective at its task... 

As for the steam cannon thing, I am not sure what the thing is still.  Does it shoot blasts of steam?  Cause the idea for my bow is that its a bow that uses steam as the propellant rather than the bowstring on a regular crossbow.  And yes, the bow is meant to fire real bolts.  I know that that can be a legal nightmare waiting to happen, but since it's only meant to be a working prop for my character rather than a weapon I'd use regularly, I can't really see much in the way of being concerned about it.  As for transporting it, I am in good with the local law enforcement, and as long as I don't have it loaded, they won't harass me about it.
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Prof. Albrecht Von Taggërt
Zeppelin Captain
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United States United States


Bettering mankind through science and engineering!


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« Reply #11 on: January 19, 2009, 09:28:46 pm »

The steam cannon would in fact shoot a blast of steam , high pressure steam to be exact. Mine is not jsut a steam cannon tho it's a Telsa Steam plasma thrower. Steam is merely there to run the small bits (a/c gen, fuel pump for the front jets etc).

I wish you luck, with this. Please do listen to Harold tho, he really does know a metric ton of info on the subject. He asl knows how things SHOULD look, when they are fake. He is desingin my backpack.
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jringling
Time Traveler
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convicted Rogue and Vagabond…long story…


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« Reply #12 on: January 19, 2009, 10:08:33 pm »

Reading through the banter and newbie bashing got me to thinking how you could have a portable steam powered contraption like the gent wants to build. CO2 weapons were mentioned, which use a stored pressurized gas. What if there was a way to produce steam at high pressure very quickly on demand. This would not require a conventional boiler, therefore you could throw out most of the complicated calculations.
We would need a water filled vessel that could withstand rapid pressurization and depressurization. Some sort of pressure regulated gate valve to dump the pressurized steam to the firing/propulsion system,  and something to flash boil the water into steam. Magnesium slug ignited by a flint striker? Some sort of electrical discharge from a capacitor bank?
The firing system would be difficult.  Is anyone familiar with air nail guns? Regular air nailers work like a stapler, pushing the nail out with a ram with enough force to sink it into wood. There is a nail gun on the market called an “Impulse” nailer which uses a fuel canister and battery . These will fire a nail out just like it was shot out of a gun. Combine this with the steam generator above and we might have a steam powered crossbow…
Any thoughts?
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The Emblasochist
Deck Hand
*
United States United States


« Reply #13 on: January 19, 2009, 10:14:49 pm »

I can see that doing something like that might be a lot more involved than you may be taking into account.  Wood isn't exactly great with rapid changes in pressure.  I personally don't know anything about nail-guns so I can't comment on that, but I can give it a try...
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Alexander Edmund Clough
Snr. Officer
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United Kingdom United Kingdom



« Reply #14 on: January 19, 2009, 10:54:50 pm »

You are not going to get it steam powered. You can't simply flash boil water to produce HP steam "just like that". Also, high pressure steam is not nice stuff, as I'm sure HAC can attest to - you really really don't want to be on the receiving end of any leaks of HP steam should your device malfunction!

Getting it to look steam powered, well that's another matter altogether, and eminently do-able.

If you want this to really fire bolts, then building a shell to house a CO2 powered speargun so that it looks like your desired "steam crossbow" is probably your best bet, and the blast of CO2 venting as it fires would certainly look steamy to an untrained eye.

But then why go to all the risk of trying to make a functioning potentially lethal weapon as a "prop"? No convention on earth would let you through the doors with a working firearm.
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So God Save the Queen, 'Cause anything is possible for a man in a top hat with a monkey with a monocle!


The Emblasochist
Deck Hand
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United States United States


« Reply #15 on: January 19, 2009, 11:02:55 pm »

Who said anything about conventions...  But I like your CO2 idea. 
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HAC
Steam Theologian
Zeppelin Overlord
*******
Canada Canada


HAC_N800
« Reply #16 on: January 19, 2009, 11:24:39 pm »

Reading through the banter and newbie bashing got me to thinking how you could have a portable steam powered contraption like the gent wants to build. CO2 weapons were mentioned, which use a stored pressurized gas. What if there was a way to produce steam at high pressure very quickly on demand. This would not require a conventional boiler, therefore you could throw out most of the complicated calculations.
We would need a water filled vessel that could withstand rapid pressurization and depressurization. Some sort of pressure regulated gate valve to dump the pressurized steam to the firing/propulsion system,  and something to flash boil the water into steam. Magnesium slug ignited by a flint striker? Some sort of electrical discharge from a capacitor bank?
The firing system would be difficult.  Is anyone familiar with air nail guns? Regular air nailers work like a stapler, pushing the nail out with a ram with enough force to sink it into wood. There is a nail gun on the market called an “Impulse” nailer which uses a fuel canister and battery . These will fire a nail out just like it was shot out of a gun. Combine this with the steam generator above and we might have a steam powered crossbow…
Any thoughts?


Hydrogen peroxide steam generation is extremely fast, lots of thermal output, and a fair b it of pressure.  basically you inject a stream of concentrated H202.  across a catalyst (usually silver gauze) pack.  In theory you could use a system like that to generate near instantaneous high pressure high temperaure steam in a  weapon chamber. The issues to overcome are the corrosiveness and toxicity of concentrated H202. You'd need a pressure system, some quick acting valves in high stainless, and lots of luck.. Another option would be pre-loaded cartridges of perxoide, with the siver catalyst being in the chamber.. The check valving would be a bit tricky, but again in theory, that could result in a portable design..

Cheers
Harold
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The Emblasochist
Deck Hand
*
United States United States


« Reply #17 on: January 19, 2009, 11:33:23 pm »

When you say in theory, I assume you haven't done it before.  I am guessing you consider doing this quite dangerous... Or is there any other reason you haven't done something like this before?  I haven't the foggiest idea about how to prepare something like what you explained, so any chance you might be willing to break it down for me?
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jringling
Time Traveler
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convicted Rogue and Vagabond…long story…


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« Reply #18 on: January 19, 2009, 11:52:28 pm »

When you say in theory, I assume you haven't done it before.  I am guessing you consider doing this quite dangerous... Or is there any other reason you haven't done something like this before?  I haven't the foggiest idea about how to prepare something like what you explained, so any chance you might be willing to break it down for me?

I doubt if anyone would have ever built such an unreliable, inefficient, and dangerous weapon. the engineering involved would be extensive and expensive. But I do like the idea...

You are not going to get it steam powered. You can't simply flash boil water to produce HP steam "just like that". Also, high pressure steam is not nice stuff, as I'm sure HAC can attest to - you really really don't want to be on the receiving end of any leaks of HP steam should your device malfunction!

I imagine anyone firing a weapon, pulling the pin on a grenade, wiring up a claymore, or packing a charge of C4 wouldn't want to be on the recieving end of a malfunction either!
Reading through the banter and newbie bashing got me to thinking how you could have a portable steam powered contraption like the gent wants to build. CO2 weapons were mentioned, which use a stored pressurized gas. What if there was a way to produce steam at high pressure very quickly on demand. This would not require a conventional boiler, therefore you could throw out most of the complicated calculations.
We would need a water filled vessel that could withstand rapid pressurization and depressurization. Some sort of pressure regulated gate valve to dump the pressurized steam to the firing/propulsion system,  and something to flash boil the water into steam. Magnesium slug ignited by a flint striker? Some sort of electrical discharge from a capacitor bank?
The firing system would be difficult.  Is anyone familiar with air nail guns? Regular air nailers work like a stapler, pushing the nail out with a ram with enough force to sink it into wood. There is a nail gun on the market called an “Impulse” nailer which uses a fuel canister and battery . These will fire a nail out just like it was shot out of a gun. Combine this with the steam generator above and we might have a steam powered crossbow…
Any thoughts?


Hydrogen peroxide steam generation is extremely fast, lots of thermal output, and a fair b it of pressure.  basically you inject a stream of concentrated H202.  across a catalyst (usually silver gauze) pack. 

Peroxide and silver metal? I shall have to look into this one. The highest [] of H2O2 I have used is 30%, nasty stuff.
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Alexander Edmund Clough
Snr. Officer
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United Kingdom United Kingdom



« Reply #19 on: January 20, 2009, 12:10:38 am »

Good point HAC - I'd clean forgotten H202 for steam generation...  Embarrassed that's the method used for the "Rocket Belt" personal jet pack doobries that started off with the Bell one and have been built and flown occasionally by loonies ever since. If I recall correctly they use 90% concentrations of H202 and upwards of 5000ft/lb of pressure for the fuel tank + two other pressurised tanks for feed, and you get at tops about 15 seconds of flight time (assuming you are the ideal weight) and 600 degree or so steam blasting down from the nozzles while the whole lot is strapped to your back. (Wheee! Sounds fun!)

90% H202 is horrible stuff. Spill it on your jeans and they'll catch fire, and it's highly caustic so you don't want to get it on your bare skin!.

Again, if I recall correctly, during WWII the germans used it as one of the fuels for one of their last-ditch rocket bomber-interceptors (the Me 163), and that had problems with in the event of a heavy landing the tanks could rupture, chucking any unspent fuel around the cockpit and burning/melting the pilot! Considering that it was an otherwise unpowered stubby glider with lightly sprung skid on the belly for landing you can imagine the risk!
« Last Edit: January 20, 2009, 12:19:20 am by Alexander Edmund Clough » Logged
Wayland2002
Snr. Officer
****
United Kingdom United Kingdom


« Reply #20 on: January 20, 2009, 12:19:58 am »

I can't see how (even with the best suspension of disbelief) how a steam mechanism is supposed to lock the nut, draw the prod, secure the string, insert the bolt and release the trigger. Even a repeating ballista required some element of human intervention.

To be honest I thought you were describing a device that shot an arrow/ bolt by using steam pressure, hence a steam canon.
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Alexander Edmund Clough
Snr. Officer
****
United Kingdom United Kingdom



« Reply #21 on: January 20, 2009, 12:25:08 am »

I can't see how (even with the best suspension of disbelief) how a steam mechanism is supposed to lock the nut, draw the prod, secure the string, insert the bolt and release the trigger. Even a repeating ballista required some element of human intervention.

To be honest I thought you were describing a device that shot an arrow/ bolt by using steam pressure, hence a steam canon.

I'm sure that a steam driven mechanism could do the job. Plenty of cams, levers and clever gear trains, plus worm screws and pulleys should do the job combined with a gravity fed hopper magazine. (e.g. have the string when drawn back enough released automatically because of a cam releasing the trigger).... Just there's no way on earth you'd get it portable or even a hand weapon.
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HAC
Steam Theologian
Zeppelin Overlord
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HAC_N800
« Reply #22 on: January 20, 2009, 12:26:32 am »

When you say in theory, I assume you haven't done it before.  I am guessing you consider doing this quite dangerous... Or is there any other reason you haven't done something like this before?  I haven't the foggiest idea about how to prepare something like what you explained, so any chance you might be willing to break it down for me?

No, I haven't and I don't think I'd want to, being a true coward in such matters. Peroxide is NASTY stuff, in the concentrations needed, you can get some pretty bad chemical burns. This type of system was used in the original Bell jet packs.
  Nearly pure (90%) hydrogen peroxide is used. Pure hydrogen peroxide is relatively stable, but in contact with the catalyst it decomposes into a mixture of superheated steam and oxygen in less than 1/10 millisecond with a volumetric increase of roughly  5000 times: ( 2 H2O2 = 2 H2O + O2) The reaction is exothermic, generating much heat (about 2500 kJ/kg), forming in a steam-gas mixture at  roughly 740 °C.
I merely mention it as an alternate method of flash steam generation.  In esssnce, you are making small bombs, so please understand if I don't elaborate. I'm not being condescending, I simply wouldn't want anyone to get hurt. (too many years of being on the railroad health and safety commitees). I also don't think you could legally acquire industrially pure peroxide (and its probably pretty pricey, to boot.)
  Steam power is dangerous, even at relatively low pressures. When I was learning the theory and practice of steam, I was taught that any boiler is an explosion looking for an excuse to happen. Steam carries  an enormous amount of energy per unit volume.  A steam burn is far worse than a hot water burn, and I speak from experience, having been grazed by the escaping steam from a pinhole leak at 250PSI , with  a fair bit of superheat. The steam was not visible until a good six feet away from the leak, as it started to condense back to hot water mist. I should have been wearing leather work  gauntlets, and long sleeves, but a momentary lapse in attention caused me a lot of pain, not to mention the loss of skin and a 3rd degree burn.

 Again, my own advice would be to make a prop weapon, far easier, probably easier to make, and probably carrying whole lot less potential legal issues, should anything happen..

Cheers
Harold
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Dr cornelius quack
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Arrant Carney. Phmebian Cultural Attache.


« Reply #23 on: January 20, 2009, 12:30:33 am »

What about a tank containing a large number of irate Bombardier Beetles?



I think this system has been used for pulse jet aircraft.

Wouldn't really recommend it though, there's already enough hot, corrosive fluids flying about in this thread as it is.

Use one of the normal methods for your projectiles, springs, elastic bands, compressed air etc and just make it look like the steam did it. (That's what the rest of us do.)

Be very clear on this point.

Live steam that is able to do useful work is also able to damage you in nasty ways, no matter what method you use to generate it.

Remember that when you produce steam at high pressure (The usefull sort) the temperature of the steam and the boiling water that creates it are raised well above the usual 1000C at atmospheric pressure.

The engineering needed to contain this pressure is serious stuff and you'd be a nutter to go wandering about with it strapped to your back.

Harold knows his stuff, and we regard him the same way that guitarists regard Eric Clapton,

He's also one of the most helpful members of the forum and gives huge ammounts of help and encouragement to those in need (that's all the rest of us.)

So,

BE NICE TO HAROLD!!

Like I said, go for the look of the thing but keep the mechanics simple. That way the job gets done quicker.

Good luck with it and post lots of WIP piccies.

Kind regards,

Dr. Q.

p.s. With reference to all the posts that were made while I was typing this,........See what I mean?
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Such are the feeble bases on which many a public character rests.

Today, I am two, separate Gorillas.
HAC
Steam Theologian
Zeppelin Overlord
*******
Canada Canada


HAC_N800
« Reply #24 on: January 20, 2009, 12:31:22 am »

I'm sure that a steam driven mechanism could do the job. Plenty of cams, levers and clever gear trains, plus worm screws and pulleys should do the job combined with a gravity fed hopper magazine. (e.g. have the string when drawn back enough released automatically because of a cam releasing the trigger).... Just there's no way on earth you'd get it portable or even a hand weapon.
True, a small steam engine (imagine the Mamod size oscillators, or single acting engines), will have a fair turn of RPM, but very little torque, due to small cross section of the pistons. In most miniature steam engines, you can stop the flywheel quite easily, so I imagine that if you could get the required mechanical advanrtage through gearing, it would be a very slow action. You could increase the torque by using
 a  near 100% cutoff in conjunction with high pressures, but again, with a small area piston, this can create more problems than it solves.
Cheers
Harold
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