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The most powerful mobile electromagnetic railgun built by a non-government

304 points by nkurz 11y ago

TerryADavis 11y ago
I am in prison. God talks. God says... pub servers parolees stability's boycotts impairs Athens's banking's corresponds semen besought uncultured sos segregation flirtation usher bacillus slices Robson mademoiselle monsters ashtray amoeba conceivably epaulettes Communion Thalia Missourian's rowdy's Rolex's Tallchief cheroot sinfully Dane illegitimacy's moonlighted excising initialization necrophilia sycophants Tonga serenading thickly grizzly Vijayawada's Seaborg sequoia's fate's replays bail Persia repeatably actress tenanted watersides undaunted impasses synapse Gujranwala glycerine Chuck Sulawesi supposition voyaging parallax personal magnolia's innovation's Beadle insensibly Camille's breadfruit's unionize authentications Faisal's slickness amenities tunefully graduation's greats cinder's halogens Hartline's downer matches oscillate isotopic Alcatraz boobies exploitative watercress sticks loanwords catnip's Israelite excitement agony decorator honorariums smuggling
junto 11y ago
I imagine that someone is going to have a visit by the FBI. That or a job offer.
- venomsnake 11y ago
  It would put interesting spin on the second amendment fights though.
- adrianN 11y ago
  Is it illegal in the US to build your own railgun? I know that in Germany there is a limit on the Joules you can put in a projectile without a licence, I think something like 8 Joules. This gun would violate that, I guess.
  - Rexxar 11y ago
    Applied strictly, this probably means that some Olympic sports require a license (hammer throw, discus throw, shot put and javelin)
    - adrianN 11y ago
      I'm pretty sure carrying a javelin around in Germany gets you in trouble. The police can get you in trouble for carrying around pocket knives if the blade is too long or locking.
      - vetinari 11y ago
        My brother used to carry gladius (in a pouch, on his back, to and from training). No cop stopped him to ask about it, ever.
        adrianN 11y ago
        Just like cops rarely stop you if you're cycling without lights after dark. If they have a reason not to like you they can still use that to slap a fine on you.
        jon-wood 11y ago
        However, I'm pretty sure if he'd started waving it at people in the street they'd have become quite a bit less lenient about the fact he was carrying a weapon around.
    - Bouncingsoul1 11y ago
      And of course also Icehockey,Football and a lot more. The german law is bit more specific about it (the exact amount of Joule is 7.5) http://www.dsb.de/media/PDF/Recht/Waffenrecht/Verwaltungsvorschrift/Verwaltungsvorschrift.pdf http://www.dsb.de/media/PDF/Recht/Waffenrecht/Verwaltungsvor... e.g. the weapon/weaponlikethingy must have a muzzle. Also the Intention of usage is considered, so if you produce a hammer with the sole purpose to throw it at me, if may offend German law.
    - amalcon 11y ago
- agumonkey 11y ago
  This or any extremist group ...
- speeder 11y ago
  There was floating on internet a very old post about how to make a railgun, made by a Brazillian guy... he DID got a job offer, but the superiors of those that tried to hire him shut it down because he was Brazillian (he was a Brazillian living in US, he wasn't allowed to legally make weapons for the government, at least for whoever tried to hire him, I don't remember anymore what department it was)
- grecy 11y ago
  In the reddit thread [1] the creator mentions many times he asked the BATF it what he was doing was OK, and they never replied. He's confident there is no law against electromagnetic weapons. He also mentions he's an engineer and has designed/built weapons that have actually been used lethally, so I get the feeling he knows what's he's talking about, professionally. [1] https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_giant_mobile_railgun_27000_joules/ https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...
  - moron4hire 11y ago
    Judging from the size of his projectiles, the bore of his device is almost certainly over 12.7mm in "diameter" (it's square, not round, but it looks to be 0.5" by 1", and I'm not about to leave the hairsplitting to a federal bureau). Classification of a "destructive device" doesn't really care what type of propellant is used. I think it's pretty clear what he has here would be considered a "destructive device". It'll depend on his state whether or not it's legal for him to have. https://en.wikipedia.org/wiki/Destructive_device https://en.wikipedia.org/wiki/Destructive_device
- DHJSH 11y ago
  Maybe Obama will invite him to the White House!
rplnt 11y ago
I parsed the title as: > Most powerful mobile railgun was built by a non-government (i.e. this is the most powerful mobile railgun) when in reality it probably is: > Most powerful mobile railgun that was built by a non-government (i.e. there are more powerful mobile railguns) Is the title ambiguous or is it just me?
- Rifu 11y ago
  The way it's written now (The most powerful mobile electromagnetic railgun built by a non-government) seems pretty non-ambiguous in implying that more powerful mobile railguns have been built by governments.
  - rplnt 11y ago
    I see, thanks. For me it can read either way (and the wrong meaning actually comes to mind first).
  - logfromblammo 11y ago
    If you want to get technical (and who doesn't?) the giant railguns mounted on navy warships are mobile. They're definitely more powerful than the device in the article. I suspect that government defense contractors have repeatedly built man-portable prototypes that just don't measure up favorably against the .50-cal rifle. The government then mothballs the project again, until better electronics technology comes along. It also seems obvious that anything that did measure up would be classified as a state secret, so we wouldn't necessarily even know about it. So the implication I got is that government-built devices are purposefully excluded, because we have no way of really knowing how powerful the most powerful government-built mobile railgun is.
Already__Taken 11y ago
> Two years were required to acquire 56 of this capacitor (This project began in February, 2013). Two more capacitors were purchased as backup, in case of failure. The total cost was $2,600. The MSRP on this type (new) is approximately $850 per capacitor ($50,000 in total). My question is who does that and cheaps out on the copper to connect them?
- madaxe_again 11y ago
  That's a lot of expense on capacitors. When we made a rail gun at school, we built our own capacitor bank with big glass cider bottles. Main problem we had was the projectile (ball bearing) welding itself to the rails. Solved by rubbing them with graphite before each firing. No idea what the efficiency was, but we lodged several bearings deep in a brick wall. They made us dismantle it as it was unsafe - so we re-use the capacitors and made a tesla coil.
  - pjc50 11y ago
    own capacitor bank with big glass cider bottles What was the construction of these - plate inside/outside made of foil?
    - madaxe_again 11y ago
      Anodised aluminium foil, borax for the electrolyte. Think we had about 30 of them. Definitely not a portable setup!
    - ethbro 11y ago
      Link for reference: https://en.wikipedia.org/wiki/Leyden_jar https://en.wikipedia.org/wiki/Leyden_jar
    - Qworg 11y ago
      Be careful with Leyden Jars - they can self charge. At size (like a 5 gallon bucket), they can carry enough charge to seriously hurt you.
  - 11y ago
TeMPOraL 11y ago
HV capacitors seem to be cheap here (Shenzhen). I guess I know what's my next side project.
- Wingman4l7 11y ago
  What's their quality control like, though?
- baldfat 11y ago
  Better get real good life insurance. I think most people fail to see all the dangers in this project. This thing terrifies me and wouldn't be within 40 feet of those capacitors. Electricity doesn't always behave the way we intended it, and this would probably be fatal if it discharges incorrectly or accidentally.
  - trymas 11y ago
    +1 Even though this project was very cool to watch, but it looked super dangerous to me, especially the capacitor bank - it looked very ghetto.
  - TeMPOraL 11y ago
    You're right, of course. I was making a joking remark here. I had enough mishaps with small HV capacitors in my childhood to know how incredibly dangerous this stuff can be (as if wasn't obvious from the sparks of molten metal on every animation there), especially that you're going to stack the capacitors to ramp the voltage up to dozens of kilovolts.
  - ceejayoz 11y ago
    > Better get real good life insurance. I strongly suspect this sort of thing is exempted in most life insurance coverage (like skydiving and flying general aviation planes usually are).
  - grecy 11y ago
    > This thing terrifies me and wouldn't be within 40 feet of those capacitors. Good for you. Sailing around the world hundreds of years ago was dangerous. Going to the moon 45 years ago was dangerous, tons of things are still VERY dangerous. Just because it's beyond your personal level of safety-acceptance, it doesn't mean there are not hundreds of people lining up to do it. You mentioning it's dangerous adds absolutely nothing to the discussion or possible learning opportunities. All you're doing is detracting from someone who's actually doing something. Rather than being so negative, why don't you go out and do something and document it as well as this guy and share it for everyone like he has?
Already__Taken 11y ago
Also if you're not concerned about the 330fps legal limit paintball markers are manufactured to you can probably adjust the regulators (not just the velocity screw you mentioned) to get a much higher initial kick. Or possibly use your own valve, that tank must output around 400-800psi before the marker regulates it down to somewhere like 200-300. And avoid feeding liquid CO2 into the marker. If there's a siphon tube in the tank it's fine that way up otherwise have the valve pointing up-ish.
sawwit 11y ago
The coming decades will surely going to be interesting as we are getting better at arbitrarily manipulating matter in a cheap way. It seems to me that the power of the individual could just become too big. There is a good reason why we decentralize important decisions: Decisions of individuals are often just too prone to errors and malice. Once individuals can synthesize viruses, armed drones, atomic bombs and AIs in their cellars, there will be a myriad ways of things going terribly wrong (in addition to the myriads of things that can already go wrong).
- fastball 11y ago
  Can't there also be a myriad of things that can go right?
  - deleted 11y ago
    [deleted]
  - mozumder 11y ago
    Has there ever been something that has gone right?
    - fastball 11y ago
      Literally the entire human race, averaged over the last 4000 years.
      - mozumder 11y ago
        All done under rules of law.
      - knieveltech 11y ago
        Slavery, genocide, and tyranny are a fact of life for many people in the world today. We haven't gotten it right yet.
  - mpweiher 11y ago
    Everything that can go right, will go right. -- Murphy was a pessimist.
mathgenius 11y ago
"The power must be monitored and disconnected before the maximum rating of the capacitors is exceeded!" As a teenager I used to love plugging in little electrolytic capacitors into the wall socket. Like, rated for 16v capacitors hit with (in australia) 240v AC. Man those things explode big time :-) I did actually try this with big capacitors (still low voltage) hoping for a proportionally bigger explosion, but those guys just fizzled. Alright, just about now I'm thankful the internetz didn't exist back then i could have done some real damage to myself. This rail-gun looks stupidly dangerous.
- scoot 11y ago
  It doesn't take mains voltage to get electrolytic capacitors to fail catastrophically. Just reverse the current. (Or rather don't). Nearly lost an eye when a kid I was paired up with in science class made that mistake. The cap blew off with a loud bang, and I was left with a perfectly symmetrical round bruise just above my eyebrow. I never forgave him. Not for nearly blinding me, but because he was happy to let everyone believe it was me who had made the mistake!
- DanBC 11y ago
  In theory big capacitors have vents so they should fizzle rather than explode.
  - HeyLaughingBoy 11y ago
    Even small ones (47uF or so) have safety slits to release overpressure. Maybe that's a recent change, though. I don't think I have any caps older than about 20 years, so I can't verify.
- DHJSH 11y ago
  I've had electrolytics blow up in my hand when I was a kid and merely powered them backward. (Back when I was a kid, BTW, 14 year olds made real digital clocks from 7400 series divider chips and nixie tubes. And we never got invited to the White House.)
ck2 11y ago
Kind of amazing you can build this and not get a visit by any government entity. Of course right now it is far less powerful that any shotgun/rifle you can buy without any background check at a gun show. We are more than a bit insane about weapons in this country.
- TeMPOraL 11y ago
  It's not a dangerous weapon for any practical purpose, because it's weak, single-shot and not portable. You wouldn't be able to say, rob a convenience store with it. Government has more dangerous things to bother with.
- mindcrime 11y ago
  We are more than a bit insane about weapons in this country. How so? We purport to be a "free country" and part of that entails the right to own weapons. Just because some people spazz out with irrational fear every time the hear the word "gun" doesn't mean that the rest of us have a problem. Consider that, by far, the vast majority of firearms owned in the US will never be used in the commission of a crime. I don't have the numbers in front of me, but somebody worked out the math and based on existing statistical trends, it's a minuscule percentage of firearms that will ever be used to commit a crime.
ris 11y ago
Somebody buy that guy a high speed camera.
adaml_623 11y ago
"During the second test, the projectile snagged before fully entering the rails and was partially reduced to a molten spray of vaporized aluminum. This issue was resolved for future launches with looser fit tolerance." For me a machine that can create a molten spray of vapourised aluminium (fixed spelling) is actually almost as interesting as a rail gun. :-) Dear FBI, purely for artistic purposes.
- yk 11y ago
  Best thing about this railgun is the optical effect. The spark shower looks like a really cheesy science fiction movie.
- thechao 11y ago
  The discovery of the elements is an interesting story. Even better, is all the craziness surrounding the naming of the elements! There are two (classical) naming methods for elements we care about for this story: those elements whose names end in -ium (strontium, gallium, et al), and those elements whose names end in -um (platinum, tantalum). Humphrey Davy (the discover of Al) originally use aluminium (1808) but, later, switched to aluminum (1812); the latter spelling became his preferred spelling. The British objected to the -um variant, and insisted on -ium. Davy (himself) seemed to consistently choose the -um variant after 1812. When the mass production of Al became feasible (another great story!) the inventor (... or, most effective capitalizer, I guess), used the -um variant; this happened in North America. Since that was the effective product name, it became the most commonly used variant in North America. Now, which is correct? The answer is: both! While I only have a few examples to look at, the dictionaries I have admit both spellings are used, and note which spelling to use in which circumstance, i.e., aluminium in Britain, and aluminum in North America. In fact, for some programs if your English locale is US then 'aluminum' is recognized as the proper spelling, and 'aluminium' is marked as 'misspelled'. However, switching your locale to UK, the opposite is true!
  - dpark 11y ago
    The original name given was not "aluminium" (nor "aluminum"), but "alumium". Wikipedia confirms this and provides citations. https://en.wikipedia.org/wiki/Aluminium#Different_endings https://en.wikipedia.org/wiki/Aluminium#Different_endings The story I've heard is that Davy started with "alumium", but added the "n" because the pronunciation was deemed too awkward, yielding "aluminum". Others pushed for "aluminium" because it sounded more consistent with other elements' names.
jokoon 11y ago
I wonder if a small railgun could be made portable for infantry, and how much power per shoot it would be. Because the home made ones don't seem that much powerful in term of muzzle energy.
- ryanmarsh 11y ago
  The only thing that looked to me like it couldn't be made smaller/lighter was that capacitor bank. Are there smaller lighter capacitors that can produce the same?
- hatsunearu 11y ago
  Capacitors have really bad energy per volume figures. People underestimate how much energy chemical stuff has--gasoline, batteries, etc.
- hderms 11y ago
  Well they're being used by the Navy now to shoot down missiles, as far as I know. I think the tradeoffs are that they are super heavy and require a lot of energy but they can accelerate projectiles extremely fast. Very useful if you're trying to shoot down something that's also moving obscenely fast but not so useful if you just want to poke a hole in a living target running at 10 miles an hour.
Kristine1975 11y ago
Reminds me of Neal Stephenson's novel "The Big U", where (among other plots) students build a railgun.
mangeletti 11y ago
This is absolutely not 27,000 joules. 27,000 joules would produce a temporary wound channel nearly large enough to destroy the ballistic gel block, and then it would travel through the entire block, sending the block a foot or two into the air. Based on the penetration of the projectile into the gel, but taking the obtuse nature of the projectile into account, I'm left to conclude this was more along the lines of 1000 joules... which makes me think the "50mph" that the author claims the CO2 provides might be more along the lines of 200mph, and that the magnetic acceleration aspect of the gun is actually doing nothing at all. In other words, we might be looking at a slightly high-powered potato gun being described by a misinformed author. Don't believe me? Take a look at the delay between the shot and the entry hole in the car door gif. That's commensurate with a projectile moving at freeway speed, not something with 27,000 joules, which for an aluminum projectile at that size, would be something like +4,000 feet per second. EDIT: Updated mph to take @avian's math into account - the ballistic gel penetration supports that as well.
- hatsunearu 11y ago
  It's probably 27kJ measured by the stored charge in the capacitor... which probably aren't delivered to the fullest extent. You can see the wires jump--that's inductive magic in action. To get any sort of quick magnetic pulse into the railgun, you need high voltage[1] and low transmission line inductance; neither of which are satisfied here. A guy I know works on high power pulse mode lasers and they achieve ridiculous rising edges with thin twisted pair wire. Lots of resistive loss but hey at least the current rising edge is nice and fast. [1]: a few kilovolts.
  - mangeletti 11y ago
    Perhaps it is, but the inefficiency of the machine shouldn't really come into play when describing how powerful it is. Otherwise, I could call my car a 900 horsepower Honda Accord, based on the gas it burns, since the engine probably isn't even close to 30% energy efficient.
    - Synaesthesia 11y ago
emeraldd 11y ago
It would be very interesting to see what could be done with a much smaller projectile. I'd imagine there's a sweet spot for maximum energy transfer and that 22grams is somewhere above that.
- kragen 11y ago
  Presumably, you would like the reverse EMF from the projectile moving through the magnetic field to provide the majority of the load voltage in the circuit and be large enough that the current continues at over half its max until the projectile makes it out of the barrel. If the projectile is too large, then you will get all of the energy out of the capacitors, but the slower motion will result in a lower back EMF, and consequently most of the energy will be dissipated resistively, probably mostly in the arc between the rails and the projectile. If the projectile is too small, then almost all of the power in the circuit will be reactive, but the projectile will leave the barrel while the capacitors are still mostly charged. Calculating this is somewhat complicated by the fact that the voltage across the projectile will be highest as it leaves the barrel, because that's when it's cutting the maximum amount of magnetic flux per millisecond; but that's exactly the point where the voltage across the capacitors is lowest, since that's when they stop discharging. Maybe you could remedy this problem by using a flywheel-driven homopolar motor instead of capacitors. Failing that, probably the best you can do is discharging the capacitors to something like half voltage, transferring three fourths of their energy into the arc and the projectile. Your two arcs, assuming a length on the order of millimeters, are going to suck up minimally 50 or so of your volts, which is one reason to use higher voltage — so that the relatively fixed voltage drop across the arcs doesn't hurt efficiency so badly. https://en.wikipedia.org/wiki/Tesla_%28unit%29 https://en.wikipedia.org/wiki/Tesla_%28unit%29 suggests that the maximum field you can reasonably expect to achieve across the rails is on the order of 500 milliteslas. If you were going to keep using 400 volts, discharged down to 200 at the time of exit, then the optimum would be to have a back EMF at 500 milliteslas of about 150 volts at whatever the muzzle velocity is. 150V / (500 mT * 20mm) = 15 km/s, about Mach 45 and about twice the speed of, say, the International Space Station. Okay, so if we have, say, 15kJ of projectile energy at 15 km/s, how massive is the projectile? 15 kJ / ((15 km/s)²/2) = 130 mg. One difficulty with this is that small, light projectiles slow down more from air resistance, which is significant when you're talking about flying fast enough to suffer ablative erosion from turning the air in front of your projectile into plasma. So, you're right. 22 grams means that the capacitors finish discharging far too early, so almost all the energy would be dissipated in the resistance of the arc. Except actually I think most of it ends up in the flapping cables, which weigh a lot more than 22 grams. You could probably get a noticeable improvement in the penetration just by tying the cables to boards so they can't flap around and generate so much back-EMF of their own. (They'll still generate a significant amount due to self-inductance, which you can reduce but not eliminate by tying the opposite-direction cables very closely together.) But wait! What if the magnetic field is weaker? Achieving 500 milliteslas is pretty hard, after all. MRI machines have a field on the order of a tesla, which creates hazards of its own, though that's mostly due to the field being distributed over a large volume. If it's only 50 mT, then you need the projectile to be going ten times as fast to build up that same 150 volts of back-EMF: 150 km/s. And that, in turn, means that your sweet-spot weight goes from 130 mg to about 40 mg. You could improve the situation for massive projectiles, at the expense of arc losses, by using a lower voltage and higher capacitance. And of course a stronger magnetic field would help too, but I don't think that's very practical. I don't know, maybe I've missed something in my calculations here. You'd think that barrel length would enter into it somewhere, for example.
grecy 11y ago
Many things are being asked that were answered by the creator in the Reddit thread yesterday. https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_giant_mobile_railgun_27000_joules/ https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...
- soylentcola 11y ago
  Yeah, only posting the image thread misses the main discussion. Thanks for the link.
clentaminator 11y ago
Metal Gear?!
aidenn0 11y ago
I suppose the author counts the University of Texas as being government? They were able to propel a 185g projectile at 1900m/s which is nearly 700kJ of projectile energy, wheras this appears to be at best 1kJ of projectile energy. [edit] Just found that in the 80s they achieved an 8.8MJ launch; their later designs were lower energy but could fire repeatedly.
- thrownaway2424 11y ago
  I believe the UT people are also behind the US Navy's railgun project. They also developed a railgun howitzer in the 90's. Perhaps that qualifies them as "government".
  - aidenn0 11y ago
    I didn't realize they were behind the Navy one too; it would be interesting to hear why they switched from flywheels to capacitors for power delivery.
leni536 11y ago
>The current flows in a C-shape through the device. This C-shape produces outward force in all directions, like water flowing through a bent rubber hose. One really shouldn't expect any measurable force from this effect. I don't claim that this effect doesn't exist, but electron mass is really small and electrons usually travel really slowly in metals (mean velocity, not to be confused with Fermi-velocity, which is usually quite large), even at relatively large currents. I can make a simple calculation for the author's construction if anyone's interested. One can build guns based on induction and Lorentz-force but I think using the electrons' inertia is completely unfeasible.
ChuckMcM 11y ago
That looks like a really fun gizmo. I'm surprised it took him that long to get the capacitors though. Another fun way of storing energy is a flywheel on an axle driving a generator. You can mechanically get the flywheel up to speed while the coil of the generator is open circuit, and then power your apparatus with it by shorting the output coil. If I did the math right and you used an old 20" car rim and weighted it up to 25kg (55 lbs) you would need to spin it at 2,500 RPM to store up 27kJ of energy. Lawn mower motor could do that, I've seen it on Battlebots :-). But perhaps more interesting slug. The NRL uses a conductive "sabot" in the gun which then launches the projectile (which is not plasma at that point) our the end. Seems like some improvement to be made there. Also there is the issue of erosion of the gun rails. How many shots before you need new rails? The best thing though is the really awesome small talk at parties, "I was tuning up the rail gun to manage the shock wave that develops on the leading edge of the slug when it goes supersonic in the barrel you know? And then I noticed hey, the plasma is creating a partial vacuum from the heat, and the shock wave I'm seeing comes when it hits the air at the end of the rails, and I think hey someone has to have solved this problem ..."

304 points by nkurz 11y ago

I am in prison. God talks. God says... pub servers parolees stability's boycotts impairs Athens's banking's corresponds semen besought uncultured sos segregation flirtation usher bacillus slices Robson mademoiselle monsters ashtray amoeba conceivably epaulettes Communion Thalia Missourian's rowdy's Rolex's Tallchief cheroot sinfully Dane illegitimacy's moonlighted excising initialization necrophilia sycophants Tonga serenading thickly grizzly Vijayawada's Seaborg sequoia's fate's replays bail Persia repeatably actress tenanted watersides undaunted impasses synapse Gujranwala glycerine Chuck Sulawesi supposition voyaging parallax personal magnolia's innovation's Beadle insensibly Camille's breadfruit's unionize authentications Faisal's slickness amenities tunefully graduation's greats cinder's halogens Hartline's downer matches oscillate isotopic Alcatraz boobies exploitative watercress sticks loanwords catnip's Israelite excitement agony decorator honorariums smuggling

junto 11y ago

I imagine that someone is going to have a visit by the FBI. That or a job offer.

venomsnake 11y ago
It would put interesting spin on the second amendment fights though.
adrianN 11y ago
Is it illegal in the US to build your own railgun? I know that in Germany there is a limit on the Joules you can put in a projectile without a licence, I think something like 8 Joules. This gun would violate that, I guess.
- Rexxar 11y ago
  Applied strictly, this probably means that some Olympic sports require a license (hammer throw, discus throw, shot put and javelin)
  - adrianN 11y ago
    I'm pretty sure carrying a javelin around in Germany gets you in trouble. The police can get you in trouble for carrying around pocket knives if the blade is too long or locking.
    - vetinari 11y ago
      My brother used to carry gladius (in a pouch, on his back, to and from training). No cop stopped him to ask about it, ever.
      - adrianN 11y ago
        Just like cops rarely stop you if you're cycling without lights after dark. If they have a reason not to like you they can still use that to slap a fine on you.
      - jon-wood 11y ago
        However, I'm pretty sure if he'd started waving it at people in the street they'd have become quite a bit less lenient about the fact he was carrying a weapon around.
  - Bouncingsoul1 11y ago
    And of course also Icehockey,Football and a lot more. The german law is bit more specific about it (the exact amount of Joule is 7.5) http://www.dsb.de/media/PDF/Recht/Waffenrecht/Verwaltungsvorschrift/Verwaltungsvorschrift.pdf http://www.dsb.de/media/PDF/Recht/Waffenrecht/Verwaltungsvor... e.g. the weapon/weaponlikethingy must have a muzzle. Also the Intention of usage is considered, so if you produce a hammer with the sole purpose to throw it at me, if may offend German law.
  - amalcon 11y ago
agumonkey 11y ago
This or any extremist group ...
speeder 11y ago
There was floating on internet a very old post about how to make a railgun, made by a Brazillian guy... he DID got a job offer, but the superiors of those that tried to hire him shut it down because he was Brazillian (he was a Brazillian living in US, he wasn't allowed to legally make weapons for the government, at least for whoever tried to hire him, I don't remember anymore what department it was)
grecy 11y ago
In the reddit thread [1] the creator mentions many times he asked the BATF it what he was doing was OK, and they never replied. He's confident there is no law against electromagnetic weapons. He also mentions he's an engineer and has designed/built weapons that have actually been used lethally, so I get the feeling he knows what's he's talking about, professionally. [1] https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_giant_mobile_railgun_27000_joules/ https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...
- moron4hire 11y ago
  Judging from the size of his projectiles, the bore of his device is almost certainly over 12.7mm in "diameter" (it's square, not round, but it looks to be 0.5" by 1", and I'm not about to leave the hairsplitting to a federal bureau). Classification of a "destructive device" doesn't really care what type of propellant is used. I think it's pretty clear what he has here would be considered a "destructive device". It'll depend on his state whether or not it's legal for him to have. https://en.wikipedia.org/wiki/Destructive_device https://en.wikipedia.org/wiki/Destructive_device
DHJSH 11y ago
Maybe Obama will invite him to the White House!

rplnt 11y ago

I parsed the title as: > Most powerful mobile railgun was built by a non-government (i.e. this is the most powerful mobile railgun) when in reality it probably is: > Most powerful mobile railgun that was built by a non-government (i.e. there are more powerful mobile railguns) Is the title ambiguous or is it just me?

Rifu 11y ago
The way it's written now (The most powerful mobile electromagnetic railgun built by a non-government) seems pretty non-ambiguous in implying that more powerful mobile railguns have been built by governments.
- rplnt 11y ago
  I see, thanks. For me it can read either way (and the wrong meaning actually comes to mind first).
- logfromblammo 11y ago
  If you want to get technical (and who doesn't?) the giant railguns mounted on navy warships are mobile. They're definitely more powerful than the device in the article. I suspect that government defense contractors have repeatedly built man-portable prototypes that just don't measure up favorably against the .50-cal rifle. The government then mothballs the project again, until better electronics technology comes along. It also seems obvious that anything that did measure up would be classified as a state secret, so we wouldn't necessarily even know about it. So the implication I got is that government-built devices are purposefully excluded, because we have no way of really knowing how powerful the most powerful government-built mobile railgun is.

Already__Taken 11y ago

> Two years were required to acquire 56 of this capacitor (This project began in February, 2013). Two more capacitors were purchased as backup, in case of failure. The total cost was $2,600. The MSRP on this type (new) is approximately $850 per capacitor ($50,000 in total). My question is who does that and cheaps out on the copper to connect them?

madaxe_again 11y ago
That's a lot of expense on capacitors. When we made a rail gun at school, we built our own capacitor bank with big glass cider bottles. Main problem we had was the projectile (ball bearing) welding itself to the rails. Solved by rubbing them with graphite before each firing. No idea what the efficiency was, but we lodged several bearings deep in a brick wall. They made us dismantle it as it was unsafe - so we re-use the capacitors and made a tesla coil.
- pjc50 11y ago
  own capacitor bank with big glass cider bottles What was the construction of these - plate inside/outside made of foil?
  - madaxe_again 11y ago
    Anodised aluminium foil, borax for the electrolyte. Think we had about 30 of them. Definitely not a portable setup!
  - ethbro 11y ago
    Link for reference: https://en.wikipedia.org/wiki/Leyden_jar https://en.wikipedia.org/wiki/Leyden_jar
  - Qworg 11y ago
    Be careful with Leyden Jars - they can self charge. At size (like a 5 gallon bucket), they can carry enough charge to seriously hurt you.
- 11y ago

TeMPOraL 11y ago

HV capacitors seem to be cheap here (Shenzhen). I guess I know what's my next side project.

Wingman4l7 11y ago
What's their quality control like, though?
baldfat 11y ago
Better get real good life insurance. I think most people fail to see all the dangers in this project. This thing terrifies me and wouldn't be within 40 feet of those capacitors. Electricity doesn't always behave the way we intended it, and this would probably be fatal if it discharges incorrectly or accidentally.
- trymas 11y ago
  +1 Even though this project was very cool to watch, but it looked super dangerous to me, especially the capacitor bank - it looked very ghetto.
- TeMPOraL 11y ago
  You're right, of course. I was making a joking remark here. I had enough mishaps with small HV capacitors in my childhood to know how incredibly dangerous this stuff can be (as if wasn't obvious from the sparks of molten metal on every animation there), especially that you're going to stack the capacitors to ramp the voltage up to dozens of kilovolts.
- ceejayoz 11y ago
  > Better get real good life insurance. I strongly suspect this sort of thing is exempted in most life insurance coverage (like skydiving and flying general aviation planes usually are).
- grecy 11y ago
  > This thing terrifies me and wouldn't be within 40 feet of those capacitors. Good for you. Sailing around the world hundreds of years ago was dangerous. Going to the moon 45 years ago was dangerous, tons of things are still VERY dangerous. Just because it's beyond your personal level of safety-acceptance, it doesn't mean there are not hundreds of people lining up to do it. You mentioning it's dangerous adds absolutely nothing to the discussion or possible learning opportunities. All you're doing is detracting from someone who's actually doing something. Rather than being so negative, why don't you go out and do something and document it as well as this guy and share it for everyone like he has?

Already__Taken 11y ago

Also if you're not concerned about the 330fps legal limit paintball markers are manufactured to you can probably adjust the regulators (not just the velocity screw you mentioned) to get a much higher initial kick. Or possibly use your own valve, that tank must output around 400-800psi before the marker regulates it down to somewhere like 200-300. And avoid feeding liquid CO2 into the marker. If there's a siphon tube in the tank it's fine that way up otherwise have the valve pointing up-ish.

sawwit 11y ago

The coming decades will surely going to be interesting as we are getting better at arbitrarily manipulating matter in a cheap way. It seems to me that the power of the individual could just become too big. There is a good reason why we decentralize important decisions: Decisions of individuals are often just too prone to errors and malice. Once individuals can synthesize viruses, armed drones, atomic bombs and AIs in their cellars, there will be a myriad ways of things going terribly wrong (in addition to the myriads of things that can already go wrong).

fastball 11y ago
Can't there also be a myriad of things that can go right?
- deleted 11y ago
  [deleted]
- mozumder 11y ago
  Has there ever been something that has gone right?
  - fastball 11y ago
    Literally the entire human race, averaged over the last 4000 years.
    - mozumder 11y ago
      All done under rules of law.
    - knieveltech 11y ago
      Slavery, genocide, and tyranny are a fact of life for many people in the world today. We haven't gotten it right yet.
- mpweiher 11y ago
  Everything that can go right, will go right. -- Murphy was a pessimist.

mathgenius 11y ago

"The power must be monitored and disconnected before the maximum rating of the capacitors is exceeded!" As a teenager I used to love plugging in little electrolytic capacitors into the wall socket. Like, rated for 16v capacitors hit with (in australia) 240v AC. Man those things explode big time :-) I did actually try this with big capacitors (still low voltage) hoping for a proportionally bigger explosion, but those guys just fizzled. Alright, just about now I'm thankful the internetz didn't exist back then i could have done some real damage to myself. This rail-gun looks stupidly dangerous.

scoot 11y ago
It doesn't take mains voltage to get electrolytic capacitors to fail catastrophically. Just reverse the current. (Or rather don't). Nearly lost an eye when a kid I was paired up with in science class made that mistake. The cap blew off with a loud bang, and I was left with a perfectly symmetrical round bruise just above my eyebrow. I never forgave him. Not for nearly blinding me, but because he was happy to let everyone believe it was me who had made the mistake!
DanBC 11y ago
In theory big capacitors have vents so they should fizzle rather than explode.
- HeyLaughingBoy 11y ago
  Even small ones (47uF or so) have safety slits to release overpressure. Maybe that's a recent change, though. I don't think I have any caps older than about 20 years, so I can't verify.
DHJSH 11y ago
I've had electrolytics blow up in my hand when I was a kid and merely powered them backward. (Back when I was a kid, BTW, 14 year olds made real digital clocks from 7400 series divider chips and nixie tubes. And we never got invited to the White House.)

ck2 11y ago

Kind of amazing you can build this and not get a visit by any government entity. Of course right now it is far less powerful that any shotgun/rifle you can buy without any background check at a gun show. We are more than a bit insane about weapons in this country.

TeMPOraL 11y ago
It's not a dangerous weapon for any practical purpose, because it's weak, single-shot and not portable. You wouldn't be able to say, rob a convenience store with it. Government has more dangerous things to bother with.
mindcrime 11y ago
We are more than a bit insane about weapons in this country. How so? We purport to be a "free country" and part of that entails the right to own weapons. Just because some people spazz out with irrational fear every time the hear the word "gun" doesn't mean that the rest of us have a problem. Consider that, by far, the vast majority of firearms owned in the US will never be used in the commission of a crime. I don't have the numbers in front of me, but somebody worked out the math and based on existing statistical trends, it's a minuscule percentage of firearms that will ever be used to commit a crime.

ris 11y ago

Somebody buy that guy a high speed camera.

adaml_623 11y ago

"During the second test, the projectile snagged before fully entering the rails and was partially reduced to a molten spray of vaporized aluminum. This issue was resolved for future launches with looser fit tolerance." For me a machine that can create a molten spray of vapourised aluminium (fixed spelling) is actually almost as interesting as a rail gun. :-) Dear FBI, purely for artistic purposes.

yk 11y ago
Best thing about this railgun is the optical effect. The spark shower looks like a really cheesy science fiction movie.
thechao 11y ago
The discovery of the elements is an interesting story. Even better, is all the craziness surrounding the naming of the elements! There are two (classical) naming methods for elements we care about for this story: those elements whose names end in -ium (strontium, gallium, et al), and those elements whose names end in -um (platinum, tantalum). Humphrey Davy (the discover of Al) originally use aluminium (1808) but, later, switched to aluminum (1812); the latter spelling became his preferred spelling. The British objected to the -um variant, and insisted on -ium. Davy (himself) seemed to consistently choose the -um variant after 1812. When the mass production of Al became feasible (another great story!) the inventor (... or, most effective capitalizer, I guess), used the -um variant; this happened in North America. Since that was the effective product name, it became the most commonly used variant in North America. Now, which is correct? The answer is: both! While I only have a few examples to look at, the dictionaries I have admit both spellings are used, and note which spelling to use in which circumstance, i.e., aluminium in Britain, and aluminum in North America. In fact, for some programs if your English locale is US then 'aluminum' is recognized as the proper spelling, and 'aluminium' is marked as 'misspelled'. However, switching your locale to UK, the opposite is true!
- dpark 11y ago
  The original name given was not "aluminium" (nor "aluminum"), but "alumium". Wikipedia confirms this and provides citations. https://en.wikipedia.org/wiki/Aluminium#Different_endings https://en.wikipedia.org/wiki/Aluminium#Different_endings The story I've heard is that Davy started with "alumium", but added the "n" because the pronunciation was deemed too awkward, yielding "aluminum". Others pushed for "aluminium" because it sounded more consistent with other elements' names.

jokoon 11y ago

I wonder if a small railgun could be made portable for infantry, and how much power per shoot it would be. Because the home made ones don't seem that much powerful in term of muzzle energy.

ryanmarsh 11y ago
The only thing that looked to me like it couldn't be made smaller/lighter was that capacitor bank. Are there smaller lighter capacitors that can produce the same?
hatsunearu 11y ago
Capacitors have really bad energy per volume figures. People underestimate how much energy chemical stuff has--gasoline, batteries, etc.
hderms 11y ago
Well they're being used by the Navy now to shoot down missiles, as far as I know. I think the tradeoffs are that they are super heavy and require a lot of energy but they can accelerate projectiles extremely fast. Very useful if you're trying to shoot down something that's also moving obscenely fast but not so useful if you just want to poke a hole in a living target running at 10 miles an hour.

Kristine1975 11y ago

Reminds me of Neal Stephenson's novel "The Big U", where (among other plots) students build a railgun.

mangeletti 11y ago

This is absolutely not 27,000 joules. 27,000 joules would produce a temporary wound channel nearly large enough to destroy the ballistic gel block, and then it would travel through the entire block, sending the block a foot or two into the air. Based on the penetration of the projectile into the gel, but taking the obtuse nature of the projectile into account, I'm left to conclude this was more along the lines of 1000 joules... which makes me think the "50mph" that the author claims the CO2 provides might be more along the lines of 200mph, and that the magnetic acceleration aspect of the gun is actually doing nothing at all. In other words, we might be looking at a slightly high-powered potato gun being described by a misinformed author. Don't believe me? Take a look at the delay between the shot and the entry hole in the car door gif. That's commensurate with a projectile moving at freeway speed, not something with 27,000 joules, which for an aluminum projectile at that size, would be something like +4,000 feet per second. EDIT: Updated mph to take @avian's math into account - the ballistic gel penetration supports that as well.

hatsunearu 11y ago
It's probably 27kJ measured by the stored charge in the capacitor... which probably aren't delivered to the fullest extent. You can see the wires jump--that's inductive magic in action. To get any sort of quick magnetic pulse into the railgun, you need high voltage[1] and low transmission line inductance; neither of which are satisfied here. A guy I know works on high power pulse mode lasers and they achieve ridiculous rising edges with thin twisted pair wire. Lots of resistive loss but hey at least the current rising edge is nice and fast. [1]: a few kilovolts.
- mangeletti 11y ago
  Perhaps it is, but the inefficiency of the machine shouldn't really come into play when describing how powerful it is. Otherwise, I could call my car a 900 horsepower Honda Accord, based on the gas it burns, since the engine probably isn't even close to 30% energy efficient.
  - Synaesthesia 11y ago

emeraldd 11y ago

It would be very interesting to see what could be done with a much smaller projectile. I'd imagine there's a sweet spot for maximum energy transfer and that 22grams is somewhere above that.

kragen 11y ago
Presumably, you would like the reverse EMF from the projectile moving through the magnetic field to provide the majority of the load voltage in the circuit and be large enough that the current continues at over half its max until the projectile makes it out of the barrel. If the projectile is too large, then you will get all of the energy out of the capacitors, but the slower motion will result in a lower back EMF, and consequently most of the energy will be dissipated resistively, probably mostly in the arc between the rails and the projectile. If the projectile is too small, then almost all of the power in the circuit will be reactive, but the projectile will leave the barrel while the capacitors are still mostly charged. Calculating this is somewhat complicated by the fact that the voltage across the projectile will be highest as it leaves the barrel, because that's when it's cutting the maximum amount of magnetic flux per millisecond; but that's exactly the point where the voltage across the capacitors is lowest, since that's when they stop discharging. Maybe you could remedy this problem by using a flywheel-driven homopolar motor instead of capacitors. Failing that, probably the best you can do is discharging the capacitors to something like half voltage, transferring three fourths of their energy into the arc and the projectile. Your two arcs, assuming a length on the order of millimeters, are going to suck up minimally 50 or so of your volts, which is one reason to use higher voltage — so that the relatively fixed voltage drop across the arcs doesn't hurt efficiency so badly. https://en.wikipedia.org/wiki/Tesla_%28unit%29 https://en.wikipedia.org/wiki/Tesla_%28unit%29 suggests that the maximum field you can reasonably expect to achieve across the rails is on the order of 500 milliteslas. If you were going to keep using 400 volts, discharged down to 200 at the time of exit, then the optimum would be to have a back EMF at 500 milliteslas of about 150 volts at whatever the muzzle velocity is. 150V / (500 mT * 20mm) = 15 km/s, about Mach 45 and about twice the speed of, say, the International Space Station. Okay, so if we have, say, 15kJ of projectile energy at 15 km/s, how massive is the projectile? 15 kJ / ((15 km/s)²/2) = 130 mg. One difficulty with this is that small, light projectiles slow down more from air resistance, which is significant when you're talking about flying fast enough to suffer ablative erosion from turning the air in front of your projectile into plasma. So, you're right. 22 grams means that the capacitors finish discharging far too early, so almost all the energy would be dissipated in the resistance of the arc. Except actually I think most of it ends up in the flapping cables, which weigh a lot more than 22 grams. You could probably get a noticeable improvement in the penetration just by tying the cables to boards so they can't flap around and generate so much back-EMF of their own. (They'll still generate a significant amount due to self-inductance, which you can reduce but not eliminate by tying the opposite-direction cables very closely together.) But wait! What if the magnetic field is weaker? Achieving 500 milliteslas is pretty hard, after all. MRI machines have a field on the order of a tesla, which creates hazards of its own, though that's mostly due to the field being distributed over a large volume. If it's only 50 mT, then you need the projectile to be going ten times as fast to build up that same 150 volts of back-EMF: 150 km/s. And that, in turn, means that your sweet-spot weight goes from 130 mg to about 40 mg. You could improve the situation for massive projectiles, at the expense of arc losses, by using a lower voltage and higher capacitance. And of course a stronger magnetic field would help too, but I don't think that's very practical. I don't know, maybe I've missed something in my calculations here. You'd think that barrel length would enter into it somewhere, for example.

grecy 11y ago

Many things are being asked that were answered by the creator in the Reddit thread yesterday. https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_giant_mobile_railgun_27000_joules/ https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...

soylentcola 11y ago
Yeah, only posting the image thread misses the main discussion. Thanks for the link.

clentaminator 11y ago

Metal Gear?!

aidenn0 11y ago

I suppose the author counts the University of Texas as being government? They were able to propel a 185g projectile at 1900m/s which is nearly 700kJ of projectile energy, wheras this appears to be at best 1kJ of projectile energy. [edit] Just found that in the 80s they achieved an 8.8MJ launch; their later designs were lower energy but could fire repeatedly.

thrownaway2424 11y ago
I believe the UT people are also behind the US Navy's railgun project. They also developed a railgun howitzer in the 90's. Perhaps that qualifies them as "government".
- aidenn0 11y ago
  I didn't realize they were behind the Navy one too; it would be interesting to hear why they switched from flywheels to capacitors for power delivery.

leni536 11y ago

>The current flows in a C-shape through the device. This C-shape produces outward force in all directions, like water flowing through a bent rubber hose. One really shouldn't expect any measurable force from this effect. I don't claim that this effect doesn't exist, but electron mass is really small and electrons usually travel really slowly in metals (mean velocity, not to be confused with Fermi-velocity, which is usually quite large), even at relatively large currents. I can make a simple calculation for the author's construction if anyone's interested. One can build guns based on induction and Lorentz-force but I think using the electrons' inertia is completely unfeasible.

ChuckMcM 11y ago

That looks like a really fun gizmo. I'm surprised it took him that long to get the capacitors though. Another fun way of storing energy is a flywheel on an axle driving a generator. You can mechanically get the flywheel up to speed while the coil of the generator is open circuit, and then power your apparatus with it by shorting the output coil. If I did the math right and you used an old 20" car rim and weighted it up to 25kg (55 lbs) you would need to spin it at 2,500 RPM to store up 27kJ of energy. Lawn mower motor could do that, I've seen it on Battlebots :-). But perhaps more interesting slug. The NRL uses a conductive "sabot" in the gun which then launches the projectile (which is not plasma at that point) our the end. Seems like some improvement to be made there. Also there is the issue of erosion of the gun rails. How many shots before you need new rails? The best thing though is the really awesome small talk at parties, "I was tuning up the rail gun to manage the shock wave that develops on the leading edge of the slug when it goes supersonic in the barrel you know? And then I noticed hey, the plasma is creating a partial vacuum from the heat, and the shock wave I'm seeing comes when it hits the air at the end of the rails, and I think hey someone has to have solved this problem ..."