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Homemade Gauss Gun 243

Posted by michael
from the physics-is-phun dept.
bonzoesc writes: "I'm sure we all remember getting owned by some railgun-wielding kid in Quake2. Ever wanted a way to get back? Enter the Homemade Gauss Rifle. Requires wooden ruler with groove down the middle to serve as the rail, steel balls that can roll down the groove to use as projectiles, and magnets to store and redirect energy. Physics is fun!"
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Homemade Gauss Gun

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  • by BrianGa (536442) on Friday March 01, 2002 @11:30PM (#3096153)
    Do Doctors (Medics) get guns that are twice as fast as those given to us, the average Joe?
  • Now I wonder if he has any patents pending. I could make it portable and market it and make millions. Seriously, though, I think I'm going to have to try this. Maybe we could do something fun like this in physics. I know it's always boring for me.. :(
  • by citroidSD (517889) <> on Friday March 01, 2002 @11:36PM (#3096171)
    I knew this would happen. First you had Physics for Game Developers [] Now you have Game Weapons for Physicists.

    Sigh, what's next, perpetual motion?
  • Make this in a tube, so that you could flex it to aim, you could shoot around corners, and just increase the length of your tubeing (and magnets) for a stronger gun.
  • Lies. (Score:5, Funny)

    by whee (36911) on Friday March 01, 2002 @11:38PM (#3096180)
    This is obviously a fake railgun; It lacks the spiral of blue particles that lead back to the source. Nice try, though.

    (At least this isn't a homemade BFG -- I'd be really scared then)

    • When I first read "gauss gun" I thought it was instructions for a rocket launcher. Too much syndicate for me!
    • Re:Lies. (Score:2, Funny)

      by bonzoesc (155812)
      Dip the steel ball on the end in blue paint before firing. Pretend that the mess on the floor is a spiral. I don't have the ball bearings handy in my dorm room to try this out, but I think you might need to make your own "PIIIIUUUU" sound effect, too.
    • A Real Railgun (Score:4, Informative)

      by HellKrisp (536404) on Saturday March 02, 2002 @09:06AM (#3097362)
      If you want to know how to build a REAL railgun, try this []. Admittedly, its a bit harder to build.
  • Hmm (Score:3, Funny)

    by FakePlasticDubya (472427) on Friday March 01, 2002 @11:41PM (#3096191) Homepage
    "But officer, you see, it's for my electrophysics class."
  • It does to 'large' objects what a Particle Accelerator does to particles.
  • by mcc (14761) <> on Friday March 01, 2002 @11:45PM (#3096204) Homepage
    Eh.. i'm disappointed. I initially misread that as "degauss rifle"..

    After discovering in computer labs that hitting the "deguass" button on a monitor will cause the monitors nearby to trip out very slightly for an instant, i had these vague daydreams of rewiring whatever it is in the monitor that makes it deguass to be unreasonably strong, so that hitting "deguass" would cause the monitors of all the computers in the lab or whatever else is in a 40-foot radius to be degaussed at once, Matrix EMP-blast style. This would probably break stuff, but then that's the point, i suppose.

    I dunno.. i guess having instructions on how to build a mini-rail-gun really is much cooler, but still, i wonder if the guass-blast idea is possible.. and if it were, modifying the idea to create a gun you could stick at a monitor and pull the trigger to deguass it would be really funny. Alas, there's no practical use for such a thing as far as i can tell, and it isn't really *that* interesting, so i don't really care enough to do any research on the subject, so for now, it looks like i'm going to have to limit myself to putting an electric pencil sharpener next to the monitor, sticking in pencils, and giggling.
    • Re:Degaussing gun (Score:2, Informative)

      by Anonymous Coward
      GO get you one of those Nifty Radio Shack degaussing "Irons" for cleanign disk and tapes
      the will do a number on a monitor at about 5 feet.
      It's nifty to look at if your into that kind of thing.
    • Re:Degaussing gun (Score:5, Informative)

      by PhuCknuT (1703) on Saturday March 02, 2002 @12:08AM (#3096271) Homepage
      What makes the monitor degauss is just a coil of wire around the edge of the screen, that has an alternating current put through it to create an alternating magnetic field. The field it creates doesn't need to extend very far, since it's wound directly around the screen.

      If you hooked up a stronger power supply to the degauss coil, you could probably degauss a couple monitors at once, but the coil would burn out quickly.

      Interesting trick though, if you ever have a monitor or tv that needs to be degaussed, that doesn't have it's own degauss coil. Hold it face to face with a monitor with a degausser, and hit the button, it will degauss them both at once.
    • so that hitting "deguass" would cause the monitors of all the computers in the lab or whatever else is in a 40-foot radius to be degaussed at once, Matrix EMP-blast style

      Well I suppose you could create some massive degausser, and it would work as long as you don't mind destroying your hard drives at the same time. Mabye you could try coupling a "bulk eraser" with some massive power supply...
      • Re:Degaussing gun (Score:5, Interesting)

        by SgtXaos (157101) on Saturday March 02, 2002 @01:02AM (#3096452) Journal
        The navy has a degaussing station near Norfolk Naval base (and probably others near big bases). They use it to degauss entire ships. The ships, being predominately steel, pick up residual magnetic fields from sailing though the earth's magnetic field. They need to periodically remove these residual fields. They float the ship in, then connect big cables over top of the vessel, and send big currents through the coils. Not sure how it affects internal equipment, but I suppose that the hull shields most of it the same way the shielding in your computer speakers prevents the voice coil magnets from screwing up your monitor.
        If you have an old color monitor you don't care about, put a magnet near the screen sometime. (ooh, a rainbow!) As this falls in the same category of fun as microwaving CDs, don't expect the degaussing circuits to fix the result anytime soon. in other words, don't do this to a monitor you wanna use.

        • Re:Degaussing gun (Score:2, Interesting)

          by Tetrad69 (526053)
          I'm not sure if this is true or not, but I heard you could manually degauss monitors with a magnet by going in circular motions from the center and working your way outward.

          So if you have an old color monitor that's messed up, you just may be able to fix it. Of course, keep the magnets away from your RAID 0+1 array...
        • ...don't do this to a monitor you wanna use.

          Around TRIUMF [], where I work, we have a lot of monitors get "gaussed" by the cyclotron's magnetic field. Most monitors around there have some pretty rainbow effects. Turns out that the degauss button available on the newer ones works pretty well to fix them.

          I'd still suggest not doing this deliberately, but if it happens there's at least hope of recovery.

        • Re:Degaussing gun (Score:2, Informative)

          by bubblegoose (473320)
          I've been through the one at Norfolk, we spent a day offloading sensitive electronic gear. Mostly the 4 or 5 PCs on board, weapons and sonar screens. Most of the electricial equipment on Navy ships are of an old design and wouldn't be affected by this. The Navy believes if it is less than 20 years old it must be some new-fangled stuff and not tested enough for their liking.

    • You can also use a large soldering iron or an electric drill to degauss monitors. A soldering iron contains a coil that generates an oscillating magnetic field at 60 Hz. I use this technique to degauss my arcade video games.

      Oh yeah, don't actually touch these things to your monitor! You're just using the magnetic fields from them, not the business ends.
    • I used to work at a hospital, near the MRI. The huge field from this thing did... interesting things to monitors. Generally we got iiyamas because they were slightly more resistant than the other makes, but the build in degaussing coil was never up to the job. One of the technicians had a high current transformer and a frame with thick copper wire wrapped round it to degauss manually.

      Computers especially close to the magnet had to be housed in a special steel alloy, referred to as 'mu' metal.

      We once got one mac, for some training software. The monitor it came with went 30 degrees sideways permanently...
  • by OverlordQ (264228) on Friday March 01, 2002 @11:46PM (#3096207) Journal
    . . . about 'Gauss Guns' can be found here []
    • by Christopher Thomas (11717) on Saturday March 02, 2002 @01:45AM (#3096609)
      Background information about 'Gauss Guns' can be found here []

      I've spotted multiple errors in this person's page. It looks like he was cribbing notes from a more informed paper.

      Problems I've found:

      • A DC solenoid attracts only ferromagnetic materials. An AC solenoid repels any conductor.

        The authour claims that coilgun coils attract the projectiles. This is not correct. They work by repulson (by Lenz's Law, the induced field in the conducting slug repels the coil's field).

      • Whinging about no exact solutions to coilgun parameter values is bogus.

        The authour does handwaving towards the 3-body problem to support his claim that you can't figure out what the best configuration of a coilgun is. These are completely unrelated problems. The 3-body problem is hard because the system a) has no general closed-form solution and b) is chaotic, so you can't even approximate a closed-form solution for many configurations.

        A coilgun, on the other hand, just has more variables than you need. You don't have one optimal coilgun - you have an infinite number of optimal coilguns. Pick some of your parameters to be convenient, and solve for the others.

        It's not hard to calculate how strong the induced field will be in a coilgun, or the force transferred to the projectile. It's also not hard to calculate how a capacitor-driven system will behave (hint: consider the coil's inductance with and without the slug inside it, and you can figure out how the energy transfer works).

      • Energy limitations apply only to military-grade coilguns.

        If you're building a tabletop coilgun, you don't have to worry about energy storage. Just get a good DC supply, set up the coils in parallel with capacitors to get a nice LC tank circuit, and set up a transistor on each coil driven off an extra turn of the coil (or a secondary coil) just as you'd set up an RF signal generator. You're going to put at most a few hundred joules into your projectile (and that's if you're heaving aluminum pipe segments across the street). Exotic solutions are only needed if you're trying to shell a neighbouring city.

      • [He gets most of the switching circuit concerns right, though an ordinary bipolar transistor works fine at tabletop energies, and switching _time_ isn't a problem - even a military weapon can get away with tenth of a millisecond timing for the coils.]

      • Ferromagnetic projectile is just dumb.

        As driving frequency goes up (or pulse length shortens), inductive effects become important. This is how a real coilgun works - it's driven by inductive repulsion of a conducting slug. If you have an iron slug, a) attractive and repulsive forces will fight each other (or you can think of it as induced currents shielding the slug from your applied magnetic field).

        Magnetic slugs only work for tabletop devices with slow firing speeds.

      • A metal sheath is asking for arcing.

        He's using a metal pipe as a guide for the projectile. A closed pipe would shield the inside of the tube just as a conducting projectile shields itself. He cuts a slot through the length of the pipe to avoid this, but you still have very high induced voltages around the pipe. A coilgun that switches at any decent speed with a strong magnetic field will induce currents that arc across this gap.

        If you want a projectile guide, use rails.

        If you want an elegant solution, let the slug move through open air and use secondary coils to adjust the geometry of the magnetic field as the projectile passes through to nudge it back into line if you notice it drifting. But this is not trivial to implement.
      • you forgot something important...

        An AC solenoid repels any conductor.
        I would pay BIG money to see a AC coil repel a piece of aluminum, copper or other non-ferrous metal.
      • After doing further research, I've come across a second operating principle used to make coilguns, which is closer to what the original poster described.

        As a conductor resists changes to the local magnetic field (Lenz's Law, cited above), if you set up a moving magnetic field, the projectile will tend to follow it.

        Note that the projectile is not "attracted into the coil", as the original article stated. Rather, if you're turning coils on and off in sequence along the gun, the projectile will be repelled by the moving field as it approaches, and dragged along with it (attracted) as it passes. The projectile *won't* just follow along with the first pulse in the moving field, either - it's just tugged briefly in the same direction. You'd have to send a train of moving field pulses over it to bring it up to the speed of the train, and it'll never quite get there (as the speed of the projectile approaches that of the moving pulse train, the pulses pass with lower frequency, so the projectile's efficiency as an inductor drops).

        You don't gain much drift-resistance, either. While the projectile is no longer actively perturbed off-axis (as with the previous style of coilgun I described), nothing keeps it on the axis either. You still need active correction (or rails).

        You're also wasting more power, because you have to keep many coils (those around the projectile) oscillating instead of just the coil behind the projectile.

        This coilgun still does not require a ferromagnetic projectile, though ferromagnetism doesn't actively harm this type of gun.
  • Uhh... (Score:5, Funny)

    by AnalogBoy (51094) on Friday March 01, 2002 @11:47PM (#3096209) Journal
    you didn't just give a bunch of undersexed, over hormonal, arrogant teenagers instructions on how to build a DANGEROUS WEAPON, now, did you?


    • Oh No!
      don't give teenagers (and/or nerds) science, cuz then the terrorist win. we must pass a vauge law to prevent any future occurance and then another one to require that some hardware be installed to prevent anyone from breaking our original vauge law.
  • I finally got the page loaded but the images are all broken. and Google don't seem to have it cached.
  • In case of /. effect (Score:3, Informative)

    by beefstu01 (520880) on Friday March 01, 2002 @11:56PM (#3096233)
    I guess this is just too damn good to pass up to be waiting for a slashdotted site to load... no pictures, but here's the text.. should satisfy your needs. Enjoy!

    Experimenting with magnetorheological fluids.
    Suspending a magnet in mid-air.
    Levitating pyrolytic graphite.
    A Gauss Rifle: A Magnetic Linear Accelerator.
    Building a Curie-effect heat engine.
    Going further:


    The Gauss Rifle:
    A Magnetic Linear Accelerator

    This very simple toy uses a magnetic chain reaction to launch a steel marble at a target at high speed. The toy is very simple to build, going together in minutes, and is very simple to understand and explain, and yet fascinating to watch and to use.

    The photo above shows six frames of video showing this toy in action. Each frame shows 1/30th of a second. In the first frame, a steel ball starts rolling towards a magnet taped to a wooden ruler. In the second frame, a second ball can be seen speeding between the rightmost two magnets. By the third frame, the accelerator has sped up so much that the ball that is seen leaving the left side of the device is just a blur as it smashes into the target. One ball, starting at rest, has caused another ball to leave the device at a very high speed.

    The materials are simple. We need a wooden ruler that has a groove in the top in which a steel ball can roll easily. Any piece of wood or aluminum or brass with a groove will work. We chose the ruler because they are easy to find around the house or at school or at a local stationery store.

    We need some sticky tape. Again, almost any kind will do. Here we use Scotch brand transparent tape, but vinyl electrical tape works just as well.

    We need four magnets. Most any type will do, but the stronger the magnets are, the faster the balls will go. Here we use the super strong gold-plated neodymium-iron-boron magnets we have made available in our catalog for the other projects. They work great.

    We will also need nine steel balls, with a diameter that is a close match to the height of the magnets. We use 5/8 inch diameter nickel plated steel balls from our catalog.

    The only tool we will need is a sharp knife for trimming the tape.

    We start by taping the first magnet to the ruler at the 2.5 inch mark. The distance is somewhat arbitrary -- we wanted to get all four magnets on a one foot ruler. Feel free to experiment with the spacing later.

    With the sharp knife, trim off any excess tape. Be careful, since the knife will be strongly attracted to the magnet.

    It is very important that you keep the magnets from jumping together. They are made of a brittle sintered material that shatters like a ceramic. Tape the ruler to the table temporarily, so that it doesn't jump up to the next magnet as you tape the second magnet to the ruler.

    Continue taping the magnets to the ruler, leaving 2.5 inches between the magnets.

    When all four magnets are taped to the ruler, it is time to load the device with the balls.

    To the right of each magnet, place two steel balls. Arrange a target to the right of the device, so the ball does not roll down the street and get lost.

    To fire the gun, set a steel ball in the groove to the left of the leftmost magnet. Let the ball go. If it is close enough to the magnet, it will start rolling by itself, and hit the magnet.

    When the gun fires, it will happen too fast to see. The ball on the right will shoot away from the gun, and hit the target with considerable force. Our one foot long version is designed so the speed is not enough to hurt someone, and you can use your hand or foot as a target.

    How does it do that?

    When you release the first ball, it is attracted to the first magnet. It hits the magnet with a respectable amount of force, and a kinetic energy we will call "1 unit".

    The kinetic energy of the ball is transfered to the magnet, and then to the ball that is touching it on the right, and then to the ball that is touching that one. This transfer of kinetic energy is familiar to billiards players -- when the cue ball hits another ball, the cue ball stops and the other ball speeds off.

    The third ball is now moving with a kinetic energy of 1 unit. But it is moving towards the second magnet. It picks up speed as the second magnet pulls it closer. When it hits the second magnet, it is moving nearly twice as fast as the first ball.

    The third ball hits the magnet, and the fifth ball starts to move with a kinetic energy of 2 units. It speeds up as it nears the third magnet, and hits with of 3 units of kinetic energy. This causes the seventh ball to speed off towards the last magnet. As it gets drawn to the last magnet, it speeds up to 4 units of kinetic energy.

    The kinetic energy is now transfered to the last ball, which speeds off at 4 units, to hit the target.

    When the device is all set up and ready to be triggered, we can see that there are four balls that are touching their magnets. These balls are at what physicists call the "ground state". It takes energy to move them away from the magnets.

    But each of these balls has another ball touching it. These second balls are not at the ground state. They are each 5/8ths of an inch from a magnet. They are easier to move than the balls that are touching the magnet.

    If we were to take a ball that was touching a magnet, and pull it away from the magnet until it was 5/8ths of an inch away, we would be adding energy to the ball. The ball would be pulling towards the magnet with some considerable force. We could get the energy back by letting the ball go.

    After the gun has fired, the situation is different. Now each of the balls is touching a magnet. There is one ball on each side of each magnet. Each ball is in its ground state, and has given up the energy that was stored by being 5/8ths of an inch from a magnet. That energy has gone into the last ball, which uses it to destroy the target.

    Speed and kinetic energy

    The kinetic energy of an object is defined as its mass times the square of its velocity. As each magnet pulls on a ball, it adds kinetic energy to the ball linearly.

    But the speed does not add up linearly. If we have 4 magnets, the kinetic energy is 4, but the speed goes up as the square root of the kinetic energy. As we add more magnets, the speed goes up by a smaller amount each time. But the distance the ball will roll, and the damage it causes to what it hits, is a function of the kinetic energy, and thus a function of how many magnets we use.

    We can keep scaling up the gun until the kinetic energy gets so high that the last magnet is shattered by the impact. After that, adding more magnets will not do much good.

    Why a circular track will not be a perpetual motion device

    I have been getting a lot of mail asking what would happen if we made the track circular. Would we get free energy? Would the balls keep accelerating forever?

    I have been tempted to reply with the famous quote: "There are two kinds of people in the world -- those who understand the second law of thermodynamics, and those who don't".

    However, I am not the kind of person to leave an inquiring mind unsatisfied, and it is more productive (and kind) to explain in a little more depth what is going on.

    Suppose you made a circular track, and put two balls after each magnet. When the last ball is released, it encounters a magnet that has two balls at the ground state. There is no energy to be had from this magnet. The ball just bounces back.

    Now suppose you had placed three balls after each magnet. When the last ball is released, it hits a ball that is 5/8ths inch from the magnet. It has not gained much momentum, because most of the momentum gained is in the last half inch as the magnet pulls much stronger on things that are closer. But the ball has enough energy from previous accelerations to release the next ball. However, that ball has less energy than the ball that caused it to release. It may have enough energy to release another ball or two, but each ball that is released has less energy than before, and eventually the chain stops.

    You can show by inductive logic that no matter how many balls you stack in front of each magnet, eventually the system stops.

    To estimate the losses due to heating the balls as they compress when hit, consider a plastic tube standing upright on a table. Place one steel ball at the bottom of the tube. Now drop another ball into the tube, so it hits the ball at the bottom, and bounces back up.

    Now measure how high the ball bounced. If it bounces halfway back up, the losses are 50%. Perform the experiment for yourself with the balls from the Gauss Rifle. How high does your ball bounce? Send me mail with your results.
  • Awesome. (Score:2, Funny)

    by Anonymous Coward
    Now can we have an article on how to make the BFG?

    C'mon, please? I wanna know the physics behind whatever the deal is with that "cone" thing.
  • by TheMonkeyDepartment (413269) on Saturday March 02, 2002 @12:12AM (#3096283)

    Dear Web Administrator:

    The editors at are about to link to your site. With your permission, we will make a site mirror available at no charge to you. This mirror will be available for the next 5 days, and will be linked from our article, sparing you thousands of simultaneous connections which might bring your puny server to a halt. By the way, we can afford to do this, because we are now charging for ad-free page views, didn't you hear?

    Please contact us by [date] and let us know if we may mirror your site. If not, the story will be published on [date] and your site may experience the "Slashdot Effect."

    • No, no no. We can get rid of the big ads and subscription service and simultaneously generate much more revenue for /. with this email:

      Dear Web Administrator

      The editors at are about to link to your site in about 4 hours. You now have three options:
      1)You may see you bandwith destroyed as tens of thousands of /.ers destroy all that you have labored to create and may your servers cry. In addition, we will post links to your site several times over the next week.
      2)You may pay us a small fee to have us set up a mirror to your site, reducing the immediate hit but only prolonging your pain to the next 24 hours.
      3)You may pay us $2000 and not have this story posted. In addition, we will not link to your site for the next 30 days.
    • the liabilty issue would be tremendous if they did this. every site ever /.ed would be calling lawyer.
      Plus, when was the last time any reported asked permission to on any thing that can be remotly considered public?
      you basically saying, hey we know your bandwidth costs will go through the roof, and your site may go down and were not taking responsibility.
      What happens when people starting saying "no I don't want you to mirror the site, and since you know you will bring my site down, I will consider it an "attack" and have my lawyers contact you.
  • Well... (Score:4, Informative)

    by Bugmaster (227959) on Saturday March 02, 2002 @12:12AM (#3096286) Homepage
    Strictly speaking, this is not a gauss gun. A real gauss gun would use the Lentz (sp?) effect or something similar to accelerate the ball down the rails; this weapon, however, is built entirely out of plain old permanent magnets and kinetic energy. Actually, I suppose that maglev trains could be considered as gigantic gauss guns also, though they do not use the Lentz effect.
    • Re:Well... (Score:5, Informative)

      by Phanatic1a (413374) on Saturday March 02, 2002 @12:59AM (#3096442)
      Well, it's a "gauss gun." Gauss = magnetic flux density. It's true that this isn't a railgun, which accelerates a projectile by means of the Lorentz force on the projectile which arises from the interaction of the current through the projectile and the magnetic field created by the passage of that current. But "gauss gun" is something of a catch-all phrase which comprises railguns, coilguns, and so forth. I guess if you wanted to you could even refer to linear induction motors as gauss guns.
  • Full-size gun (Score:2, Interesting)

    Wow, this is exceptionally clever. The only other gauss rifles I've seen talked about used electromagnets and big-ass power.

    It makes me wonder... could this scale? What if you built a big version with, say, 50 pound explosive charges (delayed fuse, of course) and big magnets? It seems like with enough phases, you could make a pretty devastating launcher. And I bet it would be pretty damn accurate, too.

    • My intuition says that such a thing would rip itself to pieces. Somebody tell us the answer.
    • It makes me wonder... could this scale?

      No, not that much. Even the very strongest permanent magnets are too weak to do much with a massive projectile. A really strong permanent magnet clocks in at around 2 T, but ~12 T is considered pretty routine with superconducting magnets.

      The advantage in a railgun is that you don't need magnets at all. The magnetic field arises purely from the passage of current. More current, a stronger magnetic field.

      Now, the very strongest magnetic fields that we can create at all are created by explosive collapse, and this achieves (brief!) field strengths of 40 T or greater. If you could time everything right, you could probably launch a helluva projectile at helluva velocities. It would be a bit of a one-shot weapon, though.

    • Re:Full-size gun (Score:3, Insightful)

      by Chagrin (128939)
      At low speeds, the elasticity of the magnets or balls isn't much of an issue as the ball clicks up against the next magnet. However, towards the end of your gun, with the balls striking the magnets at ever-increasing speeds, I think you'd start shattering everything.
    • Re:Full-size gun (Score:2, Informative)

      by einhverfr (238914)
      At some point the collisions destroy the magnets (as per the article). This can be extended by using better materials, etc.

      However there is one more limiting factor-- reloading the darned thing. So you have BIG magnets-- how do you reseat the balls between the magnets which transfer the energy. If you don't do this, you don't get the energy changes necessary to project the projectile anywhere (and you have the explosive charge....)

      This rail gun is human muscle powered and the magnets simply create a storage vessel for the energy.
      • This rail gun is human muscle powered and the magnets simply create a storage vessel for the energy.

        That's what I find interesting about this: Could it be a poor-man's (or poor country's) railgun? So what if you had to have a couple hundred slaves\\\\\\ soldiers reset the balls before firing? If you could accelerate a payload and fire a few hundred miles, it could be pretty devastating. I know that the US has some big-ass cannons that can do that, but I'm sure it's pretty tricky technology.

        Anyway, it's probably not practical given the limits of permanent magnets and the inherent wear-and-tear on every firing.

  • Don't forget the wonderful arm-mountable gauss rifles in FASA's Battletech.

    Mechs were fusion powered if I can recall correctly, so they could actually generate the massive amounts of power possible to make them somewhat feasible as a weapon.
  • by tempestdata (457317) on Saturday March 02, 2002 @12:23AM (#3096319)
    Some kid will make the gauss gun,...authorities will find out about it, and claim that he was going to use it to shoot up some kids at school.. it will be taken as further evidence that Computer games (Quake) cause violence in children... yadda yadda yadda...
  • Something similar (Score:4, Informative)

    by (463190) on Saturday March 02, 2002 @12:28AM (#3096332) Homepage
    Here's a coil gun I found on google.

    Instead of using fixed magnets to release the energy of the balls hitting each magnet in sccuession, this coil gun uses a series of timed pulses to accellerate the projectile down the length of a tube. That's a block of concrete in the photo, and I think the black spike in the top left corner is the projectile. []
  • Ok... (Score:3, Interesting)

    by cr0sh (43134) on Saturday March 02, 2002 @12:32AM (#3096345) Homepage
    From what I understand, this gun is basically the same thing as the "Newton's Pendulum" toy that clacks back and forth, but with the addition of magnets between the balls, and some distance, to cause the balls to all pick up speed so that the last one gets a lot of kinetic energy transferred to it.

    Scaling it up would seem feasible, but the problem would be the shattering magnets, as well as to "reload" you would have to physically move each ball back to the starting point.

    Here is where I wonder if this thing could be made "better". The problem is getting a magnet as strong as the ones used, but doesn't shatter - but I think it can be done...

    Get a non-ferrous tube - an alluminium or piece of PVC pipe would do fine. Get it with an inside diameter just smaller than the ball you want to fire.

    Now, wind up some "double ended" electromagnets - use very fine magnet wire, and do an excelllent job winding the magnets. Use a steel core, and wind them to the thickness of the inside diameter of the tubing. You need these electromagnets to be really strong.

    Now, cut 1.5 or 2 inch lengths of the tube - put the magnet on one end, and a ball - secure the magnets extremely well. Then, "stack" the tubes together to make a long tube, so that there is a magnet and a ball between the two magnets.

    One end (the "breech") leave a 3 inch piece of tube, and build some kind of "firing mechanism" (spring loaded or something to propel the ball against the first electromagnet). Do the same on the other end, but just the tube - no firing mechanism - you may want this end to be a little longer.

    To load and fire:

    Get a real big-ass current capacity power supply, and hook the magnets up to turn them on. Don't turn them on yet - tilt the tube up to cause all the other balls to fall to the magnets, then turn on the magnets. Load the ball on the front end (the firing chamber end), and a ball into the firing mechanism. Fire the ball - and, if everything goes right (and my back of the napkin calcs are correct - yeah right), it should do the same thing as the small version, only more powerful (maybe), and reloadable!
  • The explanation for why a circular track won't make a perpetual motion machine has some misleading statements in it. In several places he talks about "energy to be had from this magnet". However, none of the fixed magnets imparts energy to the ball.
    So where does the energy come from? Why, from your hand of course! The process of placing the balls into their starting position imparts the energy.
    • Well, the separation of the two magnets creates something similar to gravitational potential energy. The magnet that the ball is touching at rest acts as "glue" holding the ball above the magnet away from it (the anology to gravity makes this far away magnet the ground).
      • Not quite. The magnets create a magnetic "force field". As you recall from physics 101, energy is defined is force times the delta of distance, not force alone. The energy of separating the magnets is not 'released' during this experiement, as the magnets do not move. Thus, the energy comes from your hand placing the balls which move.
        Gravity also does not impart energy to falling objects; the objects already have energy relative to the earth, and actually lose energy to the earth on impact.
        • If You observe system in its initial "armed" condition you will find that it is not in its lowest possible energy configuration. Steel balls that are not immediately adjacent to magnets, do have higher potential energy than the balls touching the magnets. After firing, all the balls (except the projectile) are touching the magnets, meaning that the system has lower potential energy. The difference is the kinetic energy of the projectile.

          You are, of course, right when you say that initial energy of the system came from the hands of the person who arranged the balls.

          Now let's get semantics straight.

          >However, none of the fixed magnets imparts energy to the ball

          When the kinetic energy of the particle is enhanced at the expense of the system's potential energy (for the conservative system), the common expression in physics literature is that "field imparted energy to the particle". The expression: energy is "released" is also quite common and it simply means that system is in the configuration with lower potential energy.

          Now let's get you straight.

          >The energy of separating the magnets is not 'released' during this experiement, as the magnets do not move.

          Indeed magnets did not move, but the balls did and the potential energy of the system is lower....
  • by SevenTowers (525361) on Saturday March 02, 2002 @12:42AM (#3096378) Homepage
    Instructions to build a gun that shoots a magnet at 2KM/second. Yes you read correctly. Get a 3 meter long pipe made of pure iron. Coil 400km of thin copper wire around it. Buy a cylindrical magnet, the strongest you can get, that fits inside the pipe. Buy the fattest AC/DC converter around (or build it yourself...) and plug it in a 5000 Volt power supply (think neighbourhood electrical supply). Connect this to the 2 ends of the wires around the pipe.

    Oh ya, make sure it's pointing the right way around.

    My physics teacher did this while he was in university. They shot a concrete wall 2 feet thick and the magnet went through. The velocity was 2KM/s.
    • Wow, only FOUR HUNDRED KILOMETERS OF WIRE... and a 5000volt power supply... hold on while I start mass producing these.

      • Oh and by the way, did your physics teacher's gun explode into flames and reduce the whole thing to slag when he connected the wires to the power source?

        That wouldn't necessarily be bad, I was just wondering. :D

      • You have about 50,000 miles of blood vessels in your body. 400km doesn't seem like a whole lot in the grande scheme of things.

        5000 volts isn't hard to come by either. Ever hear of capacitors? You charge up the caps, then use them to release the power needed. Then
        charge them up again for the next shot. They could run off of wall current or any battery, it all depends on how much power it needs for the discharge that matters how often you could shoot.

    • 400km of thin copper wire is an awful lot. Try, "the width of northern Missouri".

      Wall sockets are either 110V or 220V (sometimes listed as 120V/240V). Nowhere near five thousand. Not even in Europe, where they use much higher voltages, is a wall socket five thousand volts.

      With a muzzle velocity of 2000m/s and a muzzle of only 3m, you can be damn sure that the payload would shatter and deform under the hundreds of thousands of G-forces.

      You're also neglecting the fact that at 2000m/s, air has the consistency of concrete. The payload wouldn't even get out of the muzzle. It would explode in the muzzle, you'd get a burst barrel, and you'd have 400km of fragmented copper wire bouncing around and killing anyone who was standing too close.

      At 2km/s, the concrete wall wouldn't just be breached. It would explode. Everyone around would be dead. There would also be liquified metal (from the payload) spraying everywhere, setting fires.

      The sheer amount of energy required to launch a payload at 2km/s from such a short barrel would require a current far in excess of anything THIN copper wire could bear. Not only would the barrel burst and copper go flying everywhere, the copper would be molten.

      The next time you decide to spin a totally BS yarn, please at least check to make sure the physics works.
      • by SevenTowers (525361) on Saturday March 02, 2002 @01:21AM (#3096512) Homepage
        So fuckin what if it's the width of northern missouri?

        Take a look at this page [] before talking about something you don't know about. Do you know how much energy you can get out of an electromagnetic field generated by a solenoid that's got 400km of wire? A hell of a lot. Oh, yah, do planes [] that fly at mach 7 burst into flames? It's gonna heat up like hell that's for sure. And by the way, the payload they accelerated was of the order of a few grams.

        Have you ever heard of people being in a separate room? And the concrete wall being in the middle of a room with about 10 meters of water barrels behind it.

        Don't think people are stupid before knowing the whole story. Every one aound would be dead, that has to be the stupidest I have ever heard. You check your physics dude, because expirements with explosives and high velocity projectiles happen everyday and people don't die.
        • Take a look at this page [] before talking about something you don't know about. Do you know how much energy you can get out of an electromagnetic field generated by a solenoid that's got 400km of wire?

          Rail guns and coil guns are different, they work on completely different properties of magnetics. For a rail gun you need exactly ZERO coils of copper wire. All you need are two very expensive rails, a few rare earth magnets and a huge bank of incredibly dangerous capacitors. And just a little prayer that you don't fuse your slug to your rails and waste a good $400.

          How do I know this? I actually build rail guns.
      • And who's talking about wall sockets? The voltage coming in over wires in neighbourhoods is usually 5000 volts. It gets converted down to 220 or 110 for home usage in big downconverters that are either up in the poles (big gery cylinders) or buried. The reason the voltage is so high is to reduce energy loss over long distances.
      • The armor piercing rounds of a standard American tank cannon (120mm Rheinmetall) have a muzzle velocity of around 1800m/s. The length of the barrel is around 3-4 m. So no, the payload would not shatter under the strain. And that's total bull about the air having the consistency of concrete. Like the previous poster said, we couldn't exactly expect missiles and rockets to fly at mach 4+ if they were slogging through concrete.

        Oh yes and though the voltage inside your house may be 120v, the voltage in the lines outside is much, much higher. That's why they use AC, so they can transform it.

      • The sheer amount of energy required to launch a payload at 2km/s from such a short barrel would require a current far in excess of anything THIN copper wire could bear. Not only would the barrel burst and copper go flying everywhere, the copper would be molten.

        You don't know much about physics do you?

        All the wire has to do is carry the amperage it's being fed. The energy is generated by a variation in magnetic flux. This has absolutly nothing to do with melting the wire. If the amperage is high enough, yes the wire could overheat, but since it's so long, I don't think you need that much current.
      • s = s0 + v0*t + 1/2*a*t^2 and
        v= v0 + a*t

        The final velocity, v, is 2000 m/s, so t=2000/a.

        The final distance is 3m, initial velocity and distance 0, so 3 = 1/2*a*t^2, substituting in what we know for t...

        The acceleration is six hundred and sixty-six thousand gees. From this I concur with your estimate that the 2kps story is in part a load of bullshit.

      • You are just silly as the person you are insulting.

        2000ms over a 3m barrel is not "hundreds of thousands of G's" its about 66G. Your average 24" (less than a .5m) rifle barrel acclerates a lead slug to about 1100m/s. This is about 220g. Air does not become concrete, the rifle does not explode. BTY 1G is 9.98m/s per sec.

        As for 5000v, I thought you wanted lots of amps for a solenoid, but it is a small matter to ramp up/down a voltage using a transformer (which is just two coils, one inside the other).

        So while I'm sure making a rail gun isn't that simple your "science" is just as bad. Might want to read a 1st year phyics book.

      • Dude, you might want to check you facts before insulting someone. You are wrong on so many counts. First, 2000m/s over 3m is NOT hundreds of thousands of Gs, it's roughly 65G. Second, this velocity is not out of the area of regular conventional weapons. For example the standard military M16 which shoots 5.56mm ammo has an exit velocity of around 1000m/s with powerful steel core ammo. With a gun designed for higher velocities, like a high accuracy varmit rifle, 2000m/s is not beyond reach. Air does not become concrete, and yes, 5.56 ammo from an M16 WILL punch through concrete block but no, it doesn't explode.

        What you are forgetting is that modern projectile weapons trade mass for velocity. A standard 9mm pistol fires a bullet that has a mass of only 8 grams. By rifle standards, that is huge. Your standard 5.56mm round is only about 3.5-4 grams. It sounds as if this rail gun was much the same. I don't imagine that the magnet used weighed very much.
      • 400km of thin copper wire is an awful lot. Try, "the width of northern Missouri".

        The human lung consists of bubbles that will easily cover a soccer field when (theoretically) removed and expanded. Is your chest the size of a soccer field? No? You still have that awful lot of lung bubbles with you, pal.

        Wall sockets are either 110V or 220V (sometimes listed as 120V/240V). Nowhere near five thousand. Not even in Europe, where they use much higher voltages, is a wall socket five thousand volts.
        Again, so what? These voltages can be created from the proper current. Ever heard of that nifty peronsl protection devices that send a electrical shock into the person assaulted? They're in the range of 10s of thousands volts. Yet they work in the US where there are no power outlets with these properties. There's even more surprise to it - they can operate off a 9V block battery. Generating a voltage of a few thousand is probably an easy project for someone in the physics field (which I am not, I just aenjoy a broad general knowledge).

        With a muzzle velocity of 2000m/s and a muzzle of only 3m, you can be damn sure that the payload would shatter and deform under the hundreds of thousands of G-forces.
        Weird. I remember sending a few grams of lead through a much shorter barrel (like 1 m) at speeds around 750 to 900 meters/s without shattering either the muzzle/barrel or the projectile (the projectile usually got shattered after hitting the targets). This technique is one known to man for decades and has been steadily refined to what it today. You may have guessed it, i Am talking abour assault rifles (figures are for the german G3 rifle, while other rifle, esp sniper rifles can reach higher muzzle velocitys...)

        There would also be liquified metal (from the payload) spraying everywhere, setting fires.
        Well, if this was ture, we certainly would have a military version of this thing. Liquid metal spraying everywhere and setting fires is a militarists wet dream. I am sure the payload would get quite hot and uncomfy to stop with your hand, but i think it would stay solid. The impact might lead to a rise in temperature throughout the projectile because molecular friction will jump to the max for a fraction of a second, but what the heck - even if it was cold it would be deformed by then.
  • by Matrim9 (558092) on Saturday March 02, 2002 @12:47AM (#3096400)
    mirrored, to avoid the Slashdot effect...
  • by dragons_flight (515217) on Saturday March 02, 2002 @12:51AM (#3096419) Homepage
    When I read the title, I couldn't help thinking about burned spot in one of my old dorm's carpeting. A classmate of mine build a small rail gun using electromagnets, unfortunately during a test the coils melted, which left a very interesting splotch of solidified metal and burnt carpet.
  • by Wakko Warner (324) on Saturday March 02, 2002 @12:54AM (#3096425) Homepage Journal
    It's nothing like the Quake rifle. I tried killing *THREE PEOPLE* with mine, and all it did was hit them in the head a little.

    What a waste of time!

    - A.P.
  • This is a neat little physics project, but it isn't a guass gun. A real gauss gun uses Lenz's law to propel the projectile. (It's can be a very powerful law, hehe...). The problem is that a real gauss gun of quake-like power would be much to large to carry. But they certainly are very cool.
  • by OverlordQ (264228) on Saturday March 02, 2002 @12:58AM (#3096435) Journal
    . . . although 'gauss'/'rail' guns may seem fun and interesting projects, unless your a really knowledgeable in the electical field, these are things you just shouldn't try on a large scale. You're dealing with large ammounts of heat and electricity which could explode, burn, shock and otherwise injure youself and others. Safety First!
    • Safety First!

      Actually, think for just a second: do you really want the sort of people who would half-ass the assembly of a railgun to breed? Personally, I'd rather that they eliminate themselves early in life.

      Besides, if everybody thought through every crazy stunt before they tried it, we'd put the Darwin Awards out of business.

    • One boy at the university I studied electricity, one year younger than me, died while disassembling a TV.

      Yes, you read well, he died because of remanent current in the electrical circuit (capacitor+inductive).

      When I was younger, I decided to wire a 12V DC engine to the 220V AC network. Oh and I had opened the engine. Guess what, it burned and the explosion burned my face (though lightly).

      Take care.
  • by Wonko42 (29194) <ryan+slashdot@won[ ]com ['ko.' in gap]> on Saturday March 02, 2002 @01:20AM (#3096509) Homepage
    I'm sure we all remember getting owned by some railgun-wielding kid in Quake2.

    Bah! I was that railgun-wielding kid in Quake 2!

  • by Kasmiur (464127) on Saturday March 02, 2002 @03:14AM (#3096822)
    For helping terrorist manafactur weapons that could cause mass destruction. Anyone who has viewed this page and learned something from it needs to IMMEDENTLY turn themselves into the local FBI and be detained for trial.

    This message brought to you by the Local FBI and National Security commision.

  • by MattRog (527508) on Saturday March 02, 2002 @03:30AM (#3096832)
    Back in high-school for Honors/Advanced Physics I took it upon myself to build a rail-gun, you know - something that could be cool (everyone in high-school thought Quake/Doom was the shiz) and somewhat useful (provided you needed to drive a projectile at 2 to 3 km/sec). The other students were building oh I don't know weird tinker-toys like reverse-osmosis water filtration and a electrolysis something-or-other (a guy the semester before built a tesla-coil using IBC root-beer bottles as capacitors - turned out he had wayyy more capacitance than needed and not enough current) but I wanted to make something that blew stuff up.

    So I went to work assembling materials for the gun.. I didn't worry about the math behind why rail guns worked, all I knew is that it did plenty of damage in Quake. :) So a couple hundred dollars later and I have some copper rails fixed to a base (some wood ;)), a whole lot of 2ga. wire (friend's dad worked for the electric company), and some .9F of capacitors hooked up to provide the juice.
    Two things I learned:
    1) You need a fuckton of capacitance to really achieve massive current (talking hundreds of thousands of Amps needed)
    2) You also need an electronic switch instead of a mechanical switch so you don't lose said Amps to welding the switch to itself.

    .9F of capacitance (after working out the numbers) proved to be far too few amps to do anything but make a whole lot of sparks. Actually I managed to vaporize some of the smaller projectiles with only a small scrap of what was left pitifully dribbled out of the end of the gun. In any rate, after researching further, I found some 5 and 10F capacitors which would've done the job nicely could I have afforded the several thousand dollars it required to buy one.
    So I guess the moral of the story is if you don't have $10M in defense contracts you're not going to get a good rail-gun built since it requires MASSIVE amperage to create a plasma to launch your armature out of the weapon. And Capacitors are not tiny objects, so the likelihood of a 'Eraser'-style railgun are slim to none unless someone magically comes up with a much more compact and higher-capacity capacitor (which can still discharge at 1/1000th or better of a second).

    The problem with a coil gun is that you need massive voltage plus some sizeable amps, which is generally very hard to come by. Your local mains circuit won't provide enough voltage. Although you could push it through a transformer you would need a very large and bulky one, and then you still probably would wind up with not enough amps to do the job. Most capacitors work at low enough voltages that a commodity (e.g. plugs into your regular wall socket) transformer could easily provide it, but achieving enough capacitance is both cost and size prohibitive (ignoring the rail mass loss due to vaporization).
    Stupid Quake. :)
  • Trial results (Score:2, Informative)

    by Cyberop5 (520141)
    I got bored so I tried this using Brio magnets (from the old train sets), old rusty pichinko (sp) balls, and a piece of wood trim. The results were less than stellar. but it did work after a few adjustments.

    I was able to get one of the balls off the board a few tiems, but never did it have enough force to knock over a tape dispenser. Maybe quality parts would yield better results.

  • I remeber reading a review of those cool rare earth magnets on Dan's Data [].

    The link to the article is here [] The link for where to cool magnets on his page is here []

    Now we just have to wait for a slashdotter to build a large version of this and use it to smash some watermelons :)
  • Mind now, or you'll take someone's eye out with that!
  • by ZigMonty (524212)
    The whole site [] is cool, browse around. I love the hydrogen bomb (chemical not nuclear). The levitating magnet's cool too. Now, to build that gun...
  • When in high school, a buddy of mine and I made a magnetic gun of sorts by taking magnet wire (think 24 guage, laminated, solid core wire) and wrapping it around a piece of 1/2 inch pvc pipe about eight times or so. Then, by running a very powerful DC current through the wire, it turned tha apparatus into a very powerful solenoid, of sorts. If you put a projectile in one end, turned on the power, and disconnected it before the projectile reached the middle of the tube, it would continue out the other side of the tube for some distance. I think the final version was able to shoot a small wood screw about 30 feet or so...

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