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Thread: EM Weaponry

  1. #1 EM Weaponry 
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    i am currently building my own prototype railgun, using makeshift materials for now, so i am interested in what others have to say about it.

    (just a heads up though, i know railguns are very complicated if you were to ask a scientist about it, but im going to wing it for now, please do not coment about me making one with cheap materials, just because you think it will not work.)

    anyway, please talk about anything electromagnetic. Rail guns, gauss guns, EM Launchers, ect.

    if you havnt recently there is a youtube video about a navy test fire of their own rail gun. just serch rail gun and it should be one of them.


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    I have to say I am very impressed with your endeavor. I am particularly interested in the Gauss cannon. After all mass x velocity= force. Apparently the military is working on one! :P Its going to pwn!!


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    Quote Originally Posted by the man of science
    mass x velocity= force
    I beg your pardon?
    Leszek. Pronounced [LEH-sheck]. The wondering Slav.
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    well yeah, the faster and heavier a projectile is the more lethal it can be on impact.

    thats one of the biggest appeals of EM weapons. they have the power to accelerate extreamly large and or heavy items to extream velocities that still provide ample targeting ranges.

    and i really cant be greedy with this one,
    http://www.instructables.com/id/How-to-make-a-RAILGUN!/

    for those of you with that little bit of evil genius in you
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    mass x velocity= force
    That should be mass into acceleration= force.

    I've always understood that an electromagnetic bomb is far more lethal than an EM gun.
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  7. #6  
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    Quote Originally Posted by Liongold
    mass x velocity= force
    That should be mass into acceleration= force.
    same diff
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    I've always understood that an electromagnetic bomb is far more lethal than an EM gun.
    hmm well an EMP bomb i guess would be desistating, but you really dont need electronics to fire a rail gun. all you need to run one is a power source, some capacitors, and two straight peices of metal, and some wire. it may be a little more complicated with gauss cannons, i dont know, i havnt studied them
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  9. #8  
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    Quote Originally Posted by slayer-72
    well yeah, the faster and heavier a projectile is the more lethal it can be on impact.

    thats one of the biggest appeals of EM weapons. they have the power to accelerate extreamly large and or heavy items to extream velocities that still provide ample targeting ranges.

    and i really cant be greedy with this one,
    http://www.instructables.com/id/How-to-make-a-RAILGUN!/

    for those of you with that little bit of evil genius in you
    Your damage is based on the amount of Kinetic energy, not just raw momentum.

    It's not Mass x Velocity = Damage. (This is the formula for momentum)

    It's actually (1/2) x Mass x (Velocity)^2 = Damage (Formula for kinetic energy)

    That's right. Velocity is squared in the equation for kinetic energy. That's why bullets do so much more damage than arrows. It's more important how fast the object is going when it hits than how heavy it is.

    However, there are exceptions. Sometimes the transfer of momentum is more important. (Mass x Velocity). An example would be like, if you want to give someone a concussion, vs. if you want to break their skull.

    If you want to break the skull, you want kinetic energy.

    If you want to give them a concussion, you want transfer of momentum.
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    Quote Originally Posted by the man of science
    I have to say I am very impressed with your endeavor. I am particularly interested in the Gauss cannon. After all mass x velocity= force. Apparently the military is working on one! :P Its going to pwn!!
    One can only hope that the military employ scientists of your calibre.
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  11. #10  
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    Quote Originally Posted by the man of science
    Quote Originally Posted by Liongold
    mass x velocity= force
    That should be mass into acceleration= force.
    same diff
    Err, no. If I drive my car at you at a velocity of 10m/s (north), and you are running at 10m/s, I will not catch you. If I accelerate in my car at 10m/s/s and you are running at 10 m/s, I will catch you, and I will run you over. See the difference?

    [quote="wert"]
    Quote Originally Posted by the man of science
    One can only hope that the military employ scientists of your calibre.
    lol, wert, brilliant.[/tex]
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  12. #11  
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    So, if a 2 million pound rail hits you at 5 mph, it's not going to hurt you.

    But, if something 1/10 of an ounce hits you at mach 8, you'll likely die.
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    Quote Originally Posted by kojax
    So, if a 2 million pound rail hits you at 5 mph, it's not going to hurt you.

    But, if something 1/10 of an ounce hits you at mach 8, you'll likely die.
    You're confusing force with energy. Something can hit you with very little force but still kill you because it has great kinetic energy.

    force = mass x acceleration

    but

    kinetic energy = 1/2 x mass x velocity^2

    So if
    Quote Originally Posted by kojax
    a 2 million pound rail hits you at 5 mph
    That's roughly 907184.74 kg of rail traveling at 8046.72 m/s.

    So its kinetic energy would be about 29369971130978.193 J, which, I think, is about the same amount of energy as is released when 7019 tons of TNT are blown up.

    Whereas,

    If
    Quote Originally Posted by kojax
    something 1/10 of an ounce hits you at mach 8
    That's roughly 0.00283495231 kg traveling at, well, since Mach number is simply a ratio of speeds, I'll have to improvise.

    Let's say the temperature is 10 degrees C, which will mean that Mach 8 is roughly 52 m/s.

    So our
    Quote Originally Posted by kojax
    something
    has a mass of 0.00283495231 kg and is traveling at 52 m/s.

    That's 3.83285552312 J of kinetic energy, which will lift three small apples up about three feet.

    Now I'm not sure if that's exactly right, but you get my point.
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    Hazz,


    Slight error old chap 5MPH = around 2.35 metres per second.


    And Mach 8 at sea level is around 5600mph or 15 thousand metres per second.
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    hmmm,...

    im not much for all the scientific calculating, .. i know if accelerate a small particle to extream speeds it has a much higher penetration effect, but will likely dissipate it's energy quickly. like shrapnel.

    however if you have an extreamly heavy object moving even at fairly slow speeds, it may not penetrate but the odds of it stopping any time soon are fairly slim.
    this is why longer bullets are used for sniping.


    as for weather something will kill you is usually determined by trama.
    steel core, and AP ammo can pass right through you, and (if you got the will enough) you can get right up adn keep going.

    thats why geneva banned AP ammo for regular use, because a lot of the time it only provided woundingly fatal injuries. (wounds that wounded but incapacitated).
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  16. #15  
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    Quote Originally Posted by wert
    Hazz,


    Slight error old chap 5MPH = around 2.35 metres per second.


    And Mach 8 at sea level is around 5600mph or 15 thousand metres per second.
    Oh my giddy aunt. I did say the figures might not be correct, right?

    Mach Numbers ain't my forte as you can see

    Thanks for the correction.
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  17. #16  
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    I see where I went wrong now - thanks.

    That's what you get when you're on various websites at once while using a computer calculator.
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    i still think i'd prefer a rail moving at mach 8, but i guess not every thing compremises.

    i'd still like to see about energy disipation. like i said, a smaller projectile may be able to more faster, but doesnt it lose it's momentum faster. like as apposed to the rail going all the way though you should a low surface area face hit you at 5mph, and the 1/10 ounce pellet hit you going mach 8 and only imbed it's self half way through you, the lethality is going to be leaning on the side of the rail. for a small projectile to kill you, it's either got to hit you in a vonrable spot like the brain or it has to cause trama.
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  19. #18  
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    Quote Originally Posted by Hazz
    Quote Originally Posted by kojax
    So, if a 2 million pound rail hits you at 5 mph, it's not going to hurt you.

    But, if something 1/10 of an ounce hits you at mach 8, you'll likely die.
    You're confusing force with energy. Something can hit you with very little force but still kill you because it has great kinetic energy.

    force = mass x acceleration

    but

    kinetic energy = 1/2 x mass x velocity^2

    So if
    Quote Originally Posted by kojax
    a 2 million pound rail hits you at 5 mph
    That's roughly 907184.74 kg of rail traveling at 8046.72 m/s.

    So its kinetic energy would be about 29369971130978.193 J, which, I think, is about the same amount of energy as is released when 7019 tons of TNT are blown up.
    Well, now it's time to interject some common sense.

    There's no difference between an object moving, and me being stationary vs. an object being stationary, and me moving.

    If a bullet is sitting there hovering in the air stationary, and I fly into it at 800 mph, that's the same effect as if I'm hovering in the air stationary and the bullet hits me at 800 mph.

    See the common sense problem?

    By your estimation, if I'm standing on top of a slab of rock that weighs 907184.74 kg and slip and fall, and in the process of that fall gravity accelerates my body to be moving at 5 mph at the moment I hit the ground........ I'd hit that slab of rock with the equivalent force of 7019 tons of TNT?




    Whereas,

    If
    Quote Originally Posted by kojax
    something 1/10 of an ounce hits you at mach 8
    That's roughly 0.00283495231 kg traveling at, well, since Mach number is simply a ratio of speeds, I'll have to improvise.

    Let's say the temperature is 10 degrees C, which will mean that Mach 8 is roughly 52 m/s.

    So our
    Quote Originally Posted by kojax
    something
    has a mass of 0.00283495231 kg and is traveling at 52 m/s.

    That's 3.83285552312 J of kinetic energy, which will lift three small apples up about three feet.

    Now I'm not sure if that's exactly right, but you get my point.
    In this case, common sense dictates that flichette or bullet weighing 1/10 an ounce and traveling at mach 8 should probably pierce your skin at least.

    I know most bullets weigh more than 1/10 an ounce (probably all bullets), but you get the picture?

    Quote Originally Posted by slayer-72
    hmmm,...

    im not much for all the scientific calculating, .. i know if accelerate a small particle to extream speeds it has a much higher penetration effect, but will likely dissipate it's energy quickly. like shrapnel.

    however if you have an extreamly heavy object moving even at fairly slow speeds, it may not penetrate but the odds of it stopping any time soon are fairly slim.
    this is why longer bullets are used for sniping.


    as for weather something will kill you is usually determined by trama.
    steel core, and AP ammo can pass right through you, and (if you got the will enough) you can get right up adn keep going.

    thats why geneva banned AP ammo for regular use, because a lot of the time it only provided woundingly fatal injuries. (wounds that wounded but incapacitated).
    Yeah, an advantage of heavier ammunition is that it can travel a little slower and still kill. Traveling slower means that wind resistance is less, which means you're likely to have a longer accurate range.

    I'm pretty sure wind resistance is based on your velocity cubed, whereas kinetic energy is relative to velocity squared, so a small sacrifice in kinetic energy gives you a large savings in air resistance.
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    actually wind resistance is based off of surface area. thats why most rifle rounds are longer instead of having a larger caliber. because even though you may have a larger caliber it's just going to disperse it's energy over a wide area. where as the trick to killing anything it to cause trama. thats why hunting rounds fragment and mushroom out on inpact, so they can tear and rip enough tissue for the target to bleed to death.

    bullet balistics and impact forces are really complex formulas involving so many more things than just velocity, mass, surface area and volume. most equations i would think would also involve the properties of the target.

    like you said,

    By your estimation, if I'm standing on top of a slab of rock that weighs 907184.74 kg and slip and fall, and in the process of that fall gravity accelerates my body to be moving at 5 mph at the moment I hit the ground........ I'd hit that slab of rock with the equivalent force of 7019 tons of TNT?
    what you might not think is the amount of jouels(measurement of work) generated in simple every day movement. throwing a single decent punch can generate enough jouels(i dont know how to spell it) to dent sheets of metal. but because the metal is denser, and the human flesh deforms, it will more than likely not dent it.
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  21. #20  
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    Quote Originally Posted by slayer-72
    actually wind resistance is based off of surface area. thats why most rifle rounds are longer instead of having a larger caliber. because even though you may have a larger caliber it's just going to disperse it's energy over a wide area. where as the trick to killing anything it to cause trama. thats why hunting rounds fragment and mushroom out on inpact, so they can tear and rip enough tissue for the target to bleed to death.

    bullet balistics and impact forces are really complex formulas involving so many more things than just velocity, mass, surface area and volume. most equations i would think would also involve the properties of the target.

    like you said,
    Well, both matter. A car gets worse mileage at 100 mph than it does at 60 mph because the air drag is worse. It increases with the cube of your speed.

    Of course, an aerodynamic design cuts down on wind resistance too. You basically multiply some constant related to your drag coefficient by your velocity cubed, and that tells you your drag.

    P_d = \mathbf{F}_d \cdot \mathbf{v} = {1 \over 2} \rho v^3 A C_d

    From this wiki article: http://en.wikipedia.org/wiki/Drag_(physics)

    Basically the amount of energy consumed by wind resistance is : (1/2) * (Area of object) * (drag coefficient of object) * (Density of the air) * (Velocity ^ 3)

    Using a longer bullet, with encased lead definately helps.


    By your estimation, if I'm standing on top of a slab of rock that weighs 907184.74 kg and slip and fall, and in the process of that fall gravity accelerates my body to be moving at 5 mph at the moment I hit the ground........ I'd hit that slab of rock with the equivalent force of 7019 tons of TNT?
    what you might not think is the amount of jouels(measurement of work) generated in simple every day movement. throwing a single decent punch can generate enough jouels(i dont know how to spell it) to dent sheets of metal. but because the metal is denser, and the human flesh deforms, it will more than likely not dent it.
    Yeah. I guess it has a lot to do with what deforms first, doesn't it?

    A bullet at pretty much any speed won't kill you if it can't pierce your armor, depending on how solid that armor is, of course. (I suppose a serious enough bruise *might* kill you from internal bleeding)

    Kinetic energy seems to have more of an effect on causing things to deform. That's why I say you want a high kinetic energy if you're trying to break someone's skull, but a high exchange of momentum if you're trying to give them a concussion. One favors speed. The other favors mass.

    There's a reason why some very skinny little martial artists can break boards with their hands. But, it's the big brute with a roll of quarters in his hand that gives you a concussion.
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    There's a reason why some very skinny little martial artists can break boards with their hands. But, it's the big brute with a roll of quarters in his hand that gives you a concussion
    well actually it's the same priciple. a role of nickels in your hand makes your nuckle and finger joints stretch tight. it makes the joints and ligiments of your hand less ssuseptable to jolts and impacts.

    even when you break a board you will feel less impact if your hand is tight. you yourself could probubly break a board with your hands. really the biggest trick to that is learing how to punch. mainly following through and not stoping on impact.
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  23. #22  
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    Quote Originally Posted by slayer-72
    and i really cant be greedy with this one,
    http://www.instructables.com/id/How-to-make-a-RAILGUN!/

    for those of you with that little bit of evil genius in you
    On a side note, I really doubt that this would work. It might move the little ball of foil a bit, but it's going to have a lot more to do with the electricity vaporizing some of the foil and the resulting gas pushing it around than with the lorentz force that moves the projectile in a railgun. Although my guess would be that it probably won't really move the foil at all, and just result in some partly melted foil welded to the rails.

    Edit: Having the projectile melt and/or weld itself to the rails seems to be the number one problem with railguns. Serious researchers try to get around this by making fancy projectiles from exotic materials that won't melt or spark-weld when the electricity goes through them. Home experimenters usually either end up with something that merely sprays tiny bits of molten metal, or end up with the projectile not even leaving the barrel because it gets spark welded halfway down it on the way out.
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    yeah i know i figured that out when i was testing it. it's just about total crap. there's plenty of electricity to move the projectile. i've estimated that 3 capacitors togeather can produce about 1K volts (330 volts each). the real problem is the was he tells you to make the rails, for the lorentz force to move the projectile it actaully has to be moving already. witch is a major asset to the whole thing. if it's not moving already it just welds to the rails like you said.

    however in my rail gun i was using finishing nails with the hammering end cut off.
    at first the welded to the rails, but i then make shifted a ruberband sling shot like attachment to the rails so that the projectile would be moving when it triggered..... still welded to the rails....

    i really could do more to continue my project but perhaps later. it's a real headache trying to figure out wtf is wrong with it sometimes.
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    I'm totally a novice here, but ....

    What would happen if you simply used metals that were dissimilar enough that they couldn't weld? I've been told there are some pairings of metals and/or alloys that won't bond with each other no matter how much you melt them.

    I mean, I guess that still doesn't solve the problem of having a molten projectile, I guess it being liquid still impedes the process of being able to launch it?

    Another possibility: couldn't you use something that is totally non-electric to make up most of the mass of the projectile, and then just insert a small amount of electric-reactive material into part of it? Then... I'm thinking only part of it would melt, maybe a very small part? So your projectile is mostly made of a non-electric, and only just barely part of it is electrically reactive? Would the small amount of material be enough to accelerate the rest?

    Or would that part vaporize too early, instead of launching the rest?
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    Quote Originally Posted by kojax
    Or would that part vaporize too early, instead of launching the rest?
    Just speculating, but I suspect that you would quickly melt/vaporize your small conductive section. Once the electricity stops moving through the projectile, the lorentz force stops accelerating it.

    Railguns are really hard to build. The obvious solution to the welding problem would be to use superconducing rails and projectiles so you don't get any resistive heating, but that just opens up a whole new pile of annoying problems, like how to keep everything really really cold - most people aren't going to want a railgun that can only fire when its submerged in liquid nitrogen. I think you also run into current limit problems in any of the known superconducting materials.
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  27. #26 Rail----Really??? 
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    BOY are you guys off track. First you are not going to build a real rail gun out of cheap crap out of your garage, a toy to demonstrate the principle maybe. 1st the power supply required is not just a few High voltage caps, they are HUGE, the currents involved are thousands to millions of Amps. The projectile is usually in a conductive sabot. The structure for the rail assembly has to be really really strong because the sane tremendous force accelerating the projectile is also trying to push the rails apart.
    What you know about ballistics is frightening, better go get a basic book on the subject. Powder guns are limited to about 4500 fps due to gas flow limitations.
    one thing you got right is that a Mach 8 BB will not only penetrate yor skin, the explosive impact would blow your head off.
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    just a heads up though, i know railguns are very complicated if you were to ask a scientist about it, but im going to wing it for now, please do not coment about me making one with cheap materials, just because you think it will not work
    >_>

    and as a matter of fact they do not require as much energy as you might think. they are complicated and, yes, your odds of making one from garage parts are slim if everythign goes right in the first palce. but the power is not a problem at all in this modern world. this is the classic occurance of some nay-sayer that know a little bit about the topic and come preaching around so that people will belive him.

    From:http://www.princeton.edu/~romalis/PH...n/railgun.html
    We used 12 capacitors each rated at 2000 microfarads each, charged up to 400 volts. for a total of 1920 joules. Online we found experimental evidence predicted a efficiency percentage of roughly .1% which with our capacitors would give our .2 gram armature a speed of 138 m/s (~300 mph).
    From: http://www.powerlabs.org/railgun.htm



    http://forum.allaboutcircuits.com/sh...ad.php?t=10850

    as you can easily see from just the image and the thread, 3 camera capacitors fully charged will produce around 1K jouels thats plenty of energy to move a 5-10 gram nail down 5" long rails.



    Another possibility: couldn't you use something that is totally non-electric to make up most of the mass of the projectile, and then just insert a small amount of electric-reactive material into part of it? Then... I'm thinking only part of it would melt, maybe a very small part? So your projectile is mostly made of a non-electric, and only just barely part of it is electrically reactive? Would the small amount of material be enough to accelerate the rest?
    yeah thats what's called an armeture. and it is muchly prefered over an actualy projectile in testing because if you have any decent voltage you can shoot slap through walls.


    and you really dont need the flash and glamor of super conductive rails and non bonding alloys, and ect.

    as acording to wikipedia's page on it (http://en.wikipedia.org/wiki/Railgun) reserch started on this around 1918. i dont think they had all that fancy crap when they did it.

    they may be more helpful for the durability of the railgun, and how long it lasts, but the property is still sound.
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  29. #28  
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    Quote Originally Posted by slayer-72
    just a heads up though, i know railguns are very complicated if you were to ask a scientist about it, but im going to wing it for now, please do not coment about me making one with cheap materials, just because you think it will not work
    >_>

    and as a matter of fact they do not require as much energy as you might think. they are complicated and, yes, your odds of making one from garage parts are slim if everythign goes right in the first palce. but the power is not a problem at all in this modern world. this is the classic occurance of some nay-sayer that know a little bit about the topic and come preaching around so that people will belive him.

    as you can easily see from just the image and the thread, 3 camera capacitors fully charged will produce around 1K jouels thats plenty of energy to move a 5-10 gram nail down 5" long rails.
    Camera caps are usually around 40-50 joules each, so you would need more like 20-25 of them to get a KJ. Still, getting 25 camera caps isn't a big deal; a lot of camera places will give them away for free. And you can easily buy caps that store 1 kJ each for about $40 online, so power definitely isn't the problem.

    Like you said before, it's mainly just a matter of many annoying little details that make things go wrong, even though the principle is simple. It requires a LOT of careful tinkering to get a rail gun to actually work. But of course if you are patient enough to fiddle with it until it works, you can be proud of having built something really difficult.

    Of course you aren't going to build a huge deadly cannon that can blow holes in tanks, but most people probably wouldn't want something like that in their garage anyway.
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    lol, after my prototype failed i was debating weather to jsut go big in hopes it would make things easier.

    we were going to take a bunch of microwaves apart for their capacitors and transformers , and then use small CO2 canisters as ammunition.

    from what i gather a MoT can turn 120V into 1K-2K volts, and we already have 2 of them. if it werent for the fear that im going to shock the hell out of myself(possible kill myself) i'd have done it already XD
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    Quote Originally Posted by slayer-72
    lol, after my prototype failed i was debating weather to jsut go big in hopes it would make things easier.

    we were going to take a bunch of microwaves apart for their capacitors and transformers , and then use small CO2 canisters as ammunition.

    from what i gather a MoT can turn 120V into 1K-2K volts, and we already have 2 of them. if it werent for the fear that im going to shock the hell out of myself(possible kill myself) i'd have done it already XD
    But what sort of current can the MoT put out? Remember, it's not just voltage. Current is what actually creates the magnetic fields. That chart that you posted was for some particular type of capacitor that can deliver some particular current. Simply getting to 3500 volts isn't enough to automatically get you 20 kJ of energy.
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  32. #31  
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    ah ok. well, im not real sure. nothing i ahve says how much amperage one can produce.



    though come to think of it. it's going to be very hard to even find a switch that wont break after fireing it once or twice.

    my prototype even had problems with this, evidently it was welding the parts of the switching mechanisme togeather making them stick in the on position, and eventually the switch would stop making contact because you have to tear the machanism apart breaking the welds and removing parts of the switch
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  33. #32 Re: Rail----Really??? 
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    The melting problem sounds like the most serious problem.



    Quote Originally Posted by slayer-72
    lol, after my prototype failed i was debating weather to jsut go big in hopes it would make things easier.

    we were going to take a bunch of microwaves apart for their capacitors and transformers , and then use small CO2 canisters as ammunition.

    from what i gather a MoT can turn 120V into 1K-2K volts, and we already have 2 of them. if it werent for the fear that im going to shock the hell out of myself(possible kill myself) i'd have done it already XD
    You know.... you *could* just go to Radio Shack and buy some capacitors. They're much cheaper to get that way than buying a whole camera and disassembling it.

    Or here's an online supplier I might recommend, for the combination of cheap prices and impressive selection of stuff. http://www.alltronics.com/ I'm pretty sure these guys mostly just disassemble old electronics and resell the parts, but that seems to be what you're planning to do anyway.

    Quote Originally Posted by fizzlooney
    BOY are you guys off track. First you are not going to build a real rail gun out of cheap crap out of your garage, a toy to demonstrate the principle maybe. 1st the power supply required is not just a few High voltage caps, they are HUGE, the currents involved are thousands to millions of Amps. The projectile is usually in a conductive sabot. The structure for the rail assembly has to be really really strong because the sane tremendous force accelerating the projectile is also trying to push the rails apart.
    What you know about ballistics is frightening, better go get a basic book on the subject. Powder guns are limited to about 4500 fps due to gas flow limitations.
    one thing you got right is that a Mach 8 BB will not only penetrate yor skin, the explosive impact would blow your head off.
    yours truly
    A Rocket Scientist
    Well, as long as it's being done mostly for entertainment purposes, the rail gun doesn't need to be able to blow up a tank.

    I'd be impressed if Slayer could manage just to build something strong enough to take to a shooting range and hit targets with.
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    well i'd love to make a big one. and i mean huge. perhaps later when i manage to get my own job (im still in high school ), and get up some materials. definatly after i've made the step up to one that shot a fair sized projectile though.

    im still working on collecting as many capacitors as i can. i havnt come by many, and no i dont plan on just buying cameras to take them apart. (i never knew the sold regular capacitors at radio shack i thought it was just RC cars and phones :P)

    I'd be impressed if Slayer could manage just to build something strong enough to take to a shooting range and hit targets with.
    well thats deffinatly the idea. when i first started i was planning on building one to go hunting with. if i do ever make one like that im deffinatly posting pics and vids every where

    but like i said, the hardest part of making one is really knowing how to make the rails. the rails are going to be 85% on the focus if your making a really serious rail gun. power isnt all that had, espesially when you can probubly go down to the local power supply company place and get one of those huge ass power line transformers for under (mabey) a thounsand dollars.
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  35. #34  
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    try spell check next time.
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  36. #35  
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    Well, you'd be surprised how cheap capacitors are when you buy them by themselves, especially if you just want a grab bag or something of mixed ones. Or, if you go on Ebay and do a careful search, you can find people selling rolls of like hundreds of them for twenty bucks. Where you go to get the best price just depends on what you're after.

    I'm usually happy with the selection in the Radio Shacks parts bin. Specific things I want like transformers and resistors rarely cost me more than a few cents each. 10-20 bucks will usually get you your whole project.

    I don't know much about transformers. (I'd be thinking more of a car battery, to go hunting.)

    Anyway, if you're doing this out of high school, that's impressive. I seriously hope you take engineering when you go to college. By the third physics class, you'd probably be able to rewire, and fix those microwaves instead of tearing them apart, at the rate you're going.
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    If you are looking for capacitors for a rail gun you will be looking for High capacity very, VERY low ESR types and I doubt they would be 50 bucks a roll, or even 50 bucks each. you'll be looking for the Caps similar to the ones that idiots put in their cars to try and get megawatts out of their speakers, these will be high capacity low ESR. They'll probably need an enormous ripple current rating as well,
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    Not to be a downer, but I doubt you're going to be able to get the power supply small enough to be portable on a rail gun that had enough power to hunt with. You'll probably end up with a really big, heavy power supply sitting on a table and connected to your railgun by large cables. The gun itself might be small enough to hold, but you're braver than me if you're willing to actually hold something with that much current and voltage pulsing through it.

    Have you considered making a coil gun? They're a LOT easier to construct, and you could probably make one with at least enough power to hunt small game if you're willing to spend a few bucks on high-energy capacitors. The nice thing about coil guns is that they're very tolerant; even if you do a bad job putting it together it will still probably fling the projectile, even if it's not very efficient. Then you can gradually tweak it to improve efficiency/range/whatever.
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    Quote Originally Posted by Megabrain
    you'll be looking for the Caps similar to the ones that idiots put in their cars to try and get megawatts out of their speakers, these will be high capacity low ESR.
    Those sorts of caps are usually very low voltage, so you can't discharge them very quickly. For a rail gun/coil gun you would probably want something with a high voltage and relatively low capacitance, depending on exactly how long it takes your projectile to move out of the gun.
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    Well, I see people are using banks of hundreds of 450Volt 6300uF caps on line
    I think for a first attempt I'd reccomend a 12 volt system, the components are readily available, the voltages are non-lethal, the kinetic energy attained by the missile is unlikely to kill anybody, it may also be illegal to have such a weapon in your possession.

    Take a healthy shock of 450 DC Across the heart region (hand to hand) and you die, no if's, no but's.

    Stick to 12 volts Low ESR (this reduces discharge time)

    My philosophy is simple, He's asking because he does not know, if he does not know then he should not even contemplate playing with HV electrics.
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  41. #40  
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    Quote Originally Posted by Megabrain
    Well, I see people are using banks of hundreds of 450Volt 6300uF caps on line
    I think for a first attempt I'd reccomend a 12 volt system, the components are readily available, the voltages are non-lethal, the kinetic energy attained by the missile is unlikely to kill anybody, it may also be illegal to have such a weapon in your possession.
    12 volts probably just wouldn't be enough to get enough current to move the projectile in a rail gun. You need want hundreds or thousands of amps. At only 12 volts, you just wont be able to get enough current.
    Take a healthy shock of 450 DC Across the heart region (hand to hand) and you die, no if's, no but's.

    Stick to 12 volts Low ESR (this reduces discharge time)

    My philosophy is simple, He's asking because he does not know, if he does not know then he should not even contemplate playing with HV electrics.
    There's no question that these power supplies are very deadly; we're not just talking "you're instantly electrocuted," we're talking "you're instantly electrocuted and the current explodes the hand that was touching it."

    But, that's usually what it takes to actually make a rail gun work. Messing around with 12 V would probably just be a waste of time. Although I certainly would recommend that someone not attempt anything like this unless they are sure they know exactly what they're doing.
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    The important thing is transferring power to the load, for this it might be a good idea to have a grasp of Maximum Power Transfer Theorum, where essentially the source and load impedance should match (if purely resistive) or, as would be the case here the complex conjugate (hence a capacitor 'feeding' an inductor).

    The important thing in all this is that the source impedance of the supply should be as low as possible, that naturally occurs (for any given generator power) with a lower voltage

    I see no mathematics to support your assertion that a higher voltage is more preferable, I could have missed something though...
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    Um, how about I=V/R?

    The lorentz force exerted on the projectile will, if I'm remember right, by proportional to the square of the current traveling through the rails and armature - so to move the projectile you want a very very high current. The resistance of the rails and armature will be pretty high, especially since the electricity will probably have to actually arc from the rail to the projectile to the other rail one the current starts flowing and the outer layer of the armature is vaporized. It will take hundreds or thousands of amps to move the projectile. Your total resistance across the rails and the armature will be fairly high, so you simply MUST have a high voltage, or you won't get enough current flowing to generate a useful lorentz force.
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    so how does that make it better for a low voltage?

    V = I*R is true for any DC voltage it neither favours high nor low voltage.

    The resistance of the rails is low, very very low the lower the better.

    Since I = V/R for any given voltage the Current is inversely proportional to the voltage thus the lower the resistance the higher the current, the exact opposite of your assertion 8)
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  45. #44  
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    Quote Originally Posted by Megabrain
    so how does that make it better for a low voltage?

    V = I*R is true for any DC voltage it neither favours high nor low voltage.

    The resistance of the rails is low, very very low the lower the better.

    Since I = V/R for any given voltage the Current is inversely proportional to the voltage thus the lower the resistance the higher the current, the exact opposite of your assertion 8)
    No, my assertion is that you need high voltage to get high current because the resistance WILL be high. Low resistance would be nice, but is not really an option.
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  46. #45  
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    Would it make any difference to have multiple very thin rails close to each other? (Assuming you could brace them somehow so they stayed in place)

    Would that have the same effect as adding multiple turns to a coil electromagnet, and increase the amount of magnetic force?
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    um i dont think so, it might actaully make it to the current might bridge between the multiple rails making the gun less efficient. but that does give me an interesting idea. im woundering what might happen if i aranged 4 rails togeather in a "+" like arangement. having positive on the top and bottom rails and negative on the left and right rails.


    and yeah im either going to be using steel of aluminum rails, so im predicting that resistance will be fairly high. a low voltage might be ok for testing to make sure the rails are opperating, like in just giving the projectile a tiny push to know if it's working, but if i were to actually shoot somethign with it, a much higher voltage will be required. (btw, does any one ahve a chart or graph on hand that will tell me the lethality of electrical shocks based on voltage, the way i've always thought it was was that your body can take lots ov volts, persay in the thousands, with out dieing, but getting hit with one amp will be enough to kill you. )

    as for a coil gun, i was thinking about trying it later, i might put my rail gun on hold for a little bit to try one. i have heard they are much easier to build, requireing mainly only a pipe and some coiled wire, but as of yet i havnt done a lot of reserch on them.


    (edit: woot 4th page )
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  48. #47  
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    I think the positioning of the rails is important. Having the projectile set between exactly 2 rail locations ensures that the fields from the 2 rails will always reinforce, and never cancel, in the area between those rails.

    It's the right hand rule. Magnetic field lines form in a circle around the wire, and face in the direction along that circle which your fingers would point if you pointed the thumb of your right hand in the direction the current is traveling, and wrapped your fingers around the wire.

    Because the current is going in opposite directions through the two rails, these field lines always reinforce in the area where the projectile is at. What I was suggesting was to still have just 2 locations, but at each location you put a lot of separate rails. The current traveling through each rail counts separately.


    But what I'm wondering though: Is the fact there's never any field in front of the projectile important?

    I mean, since the projectile is completing the circuit, there's no current flowing through the area of the rails where the projectile hasn't reached yet, so the magnetic field only forms behind it. Is that an important part of the effect, or just a detail?
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  49. #48  
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    What I meant is that , in the area between two + charged rails (or two - charged rails), the magnetic fields actually cancel each other out. So, if you use 4 rails, you'll still want to arrange them so that they're in just 2 locations, because otherwise you probably won't be getting the maximum magnetic force you could get.
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    oh ok. that makes sense.

    anyway, i was rethinking that multiple rails thing about having many smaller rails in the same place as the two larger rails. im not real sure if it would do anything. could any one here with more knowlage of elctricity elaborate for me

    btw, does any think, perhaps, a copper pipe cut in half down the pipe would make an ok rail design?
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  51. #50  
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    Yeah, it probably doesn't do anything. I was thinking of how it works in coils. The wires being close to each other amplifies the effect without costing more electricity, because the same current is passing through the same area multiple times.

    But for a rail gun, that wouldn't work like I'm thinking. Not unless you could find a way to route the same current so that it's continually re-feeding through the wires/mini rails again and again.
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  52. #51  
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    something i've been thinking about lately is what supplies i was going to use for my higher voltage rail gun.

    so far they are as listed:

    copper pipe rail
    6oz CO2 cartridge as a bullet
    2-3 microwave transformers
    + 2-3 microwave capacitors
    still need to find a few good switches
    ect.


    but what i've been wondering is weather or not the high voltages of the rail gun will make the CO2 cartridge unusable as a round, i know that they say somewere on them not to use/store in extream heat.(as any compressed gas) this posses a problem on the heat that will come from the voltage jumping from the rails to the cartridge. i've seen the nails welded to my previous rail system because of a failure, and im not sure if these heats will be dangerous to the integrity of the cartridge. in other words im afraid they will explode should the rails short, or even if they do fire, because of the heat.
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  53. #52  
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    Might want to build yourself a remote switch, and activate it from very far away. I wouldn't want to be near that thing if it does blow up.


    A possibility I'm wondering about: What if the rails aren't what you use to apply electricity to the projectile?

    Could you use a pair of very wide, flat pieces of metal that connect to the power supply at multiple points along their length (So the current isn't flowing in any one direction as it travels through them to get to the projectile) as the means of applying electricity?

    Then, just have the rails be a separate thing that never comes into contact with your projectile at all.
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  54. #53  
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    no i dont think that would work.

    from what i know, the idea is that the conection has to be briged by either the projectile or an armeture. mabey because thast the only way to keep the magnetic field on the right axis, beacause i noticed that the projectile seems to take on some magnetic abilities it's self. like i had one nail i could pick up for a couple seconds with magnatism after trying to shoot it.



    btw, is all you really need for a coil gun to work, is a coil of wire at one end of a pipe, and an electric source? and when you turn on the electric, it creates a magnetic fiedl around the coils and that pulls the projectile out of the barrel?
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  55. #54  
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    Quote Originally Posted by slayer-72
    btw, is all you really need for a coil gun to work, is a coil of wire at one end of a pipe, and an electric source? and when you turn on the electric, it creates a magnetic fiedl around the coils and that pulls the projectile out of the barrel?
    Basically yes. The coil will try to pull the projectile to its center. The idea is to send a pulse of electricity through the coil that causes the projectile to shoot forward into it, but cut the pulse off right before it reaches the center (otherwise it would start to slow down). Usually people use a capacitor to send the current pulse through the coil.
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  56. #55  
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    ok, just wanted to make sure. i was going to try one of those pretty soon, since it's much easier to build. but how many coils would you recomend? i would think the more coils the larger the round you could fire, but would have to cut it off sooner?
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  57. #56  
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    The force exerted on the projectile will depend on the current going through the coil, the number of turns in the coil, and how close the turns are to the projectile (so the 2nd layer will have less effect than the first layer, etc). Thinner wire gets you more turns, which is good, but it will also have a higher resistance, which is bad. So you have to figure out the right balance between wire thickness, number of turns, etc. So far as I know there isn't any easy way to figure out the optimum setup. Most people just experiment by making several different types of coil and seeing which works best for their power supply and projectile.

    As for more than one coil, I think it depends on what kind of power switching you have and how much energy it can handle. If you can dump all your power into one coil, I would probably do that to keep it simple. If you have more power than a single stage can handle, you can spread it over multiple coils.
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