Building a Rail Gun

[Valentin] tipped us about his latest project: a homemade railgun. For the few that may not know already, a railgun is an electrically powered electromagnetic projectile launcher. It is comprised of a pair of parallel conducting rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail. [Valentin]’s writeup starts with a detailed explanation of this principle, then a simple proof of concept is shown where a metal stick with two small round magnets on each end is accelerated along two alumium strips powered by a 9V battery.

The final build shown above is powered by a capacitor bank consisting of three 400V 2200uF capacitors in parallel. [Valentin] opted for a hot rail design, where the power is always present on the rails. The projectile is inserted into the assembly by a spring-loaded lever. A video is embedded after the break. If you found this interesting, you’re going to love the fully-automatic Gauss gun.

35 thoughts on “Building a Rail Gun

  1. Yeah.

    This is the kind of story that makes me cringe. Crappy build made from junk parts? Check. Extremely high voltages? Check. Article that makes it seem “fun” and “easy” to build your own without a reasonable forewarning that this thing COULD KILL YOU? Check.

    Sorry, but this isn’t cool, it’s stupidly dangerous. The complete and utter lack of safety warnings especially considering his “hot rail” design makes me respect this build even less. I’m even more surprised that Hackaday hasn’t said anything about this either.

    -SC

    1. oddly, I didn’t react in horror when I read this write-up. it seems patently obvious that you’re dealing with lethal voltages here, enough so that warnings just don’t seem necessary. but then, knowing some people, perhaps that’s just the scenario where warnings are truly needed. either way, kids, don’t try this at home. or take precautions if you do. whatever.

        1. i have to let you guys know that the voltage DOESN’T kill you!!!!! Its the Amps which do!!!!! and consider your body is a high resistance it would take a big voltage to kill you.

          1. That’s why I wrote “high enough to be fatal if they cause a current”. 400V is more than enough to cause dielectric breakdown in your skin, which can cause the current to enter your body and cross your heart. 9V won’t do this, but it can be dangerous if it could bypass your skin (say, if electrodes pierced your skin).

    2. True.., but then I would hope common sense would prevail for anyone attempting this sort of thing, and if not, does it count as a Darwin Award?

      I haven’t watched the video yet, but I’m asuming the power output @400V is very high to be dangerous though (as opposed to things like Van de graaff gens which put out well over a million volts and hardly feel like a tingle, and stun guns/tasers which put out 25k-500k volt, and are still harmless… ish.)?

    3. “Extremely high voltages?”
      “fun”
      “easy”
      “build your own”
      “COULD KILL YOU?”

      “Sorry, but this isn’t cool”

      wait, what? I thought you pretty much just defined how cool this was…

    4. There is a big yellow danger sign on the first frame of the video. You see these signs on power grid installations, “Danger of Death” often accompanies as textual information. People still go in and get killed. Many things are dangerous but people still do them despite the warnings. Like playing with weapons whilst drunk or on drugs. :(

    5. If we always choose to do only that which isn’t dangerous, we could have gotten nowhere in science.

      Personally They guy is working with what he has access to, which I like to see.. Tis hacking at its best.

    6. Why does everything have to be slathered in disclaimers and warnings these days? Morons should not be protected from the effects of their idiocy, it pollutes the gene pool allowing obvious candidates for elimination to persist and procreate.

      1. “Morons should not be protected from the effects of their idiocy, it pollutes the gene pool allowing obvious candidates for elimination to persist and procreate.”

        That’s an excellent motto.. think I’ll print this on a large poster and hang it in our lab. :-)

    7. My physics teacher let me build a rail-gun for extra credit which was only slightly safer than this, if at all. He plugged it in, dropped a construction nail into the gravity fed barrel, and when the nail slid down the barrel and hit the contact plate ZOT! the nail lobbed out onto the floor and the breaker blew and the lights went out. SUCCESS! Extra credit!

      1. One of my college professors always liked to do the “Which wins, tin foil or the wall socket?” experiment. He’d pretty regularly get the size of the foil a bit too large and blow the breaker :)

    8. This is definitely a cool video but I cringed a little when he was playing with those Caps. This could be a killer project. Pun intended. It needs a little more talk about safety.

  2. Best explanation i have seen of how rail-guns of this simple type work. It uses 3x 400V 2200uF capacitors. You can get these (and bigger) cheap from scrapped cars, or on ebay new £60. Voltages LETHAL, also so potentially is the projectile!

    Energy E = (C *( V^2))/2 | so | E=(0.0022*( 400^2)) /2 = 176 Joules (J) * 3 = 528 J.

    528J ! assuming a 10g mass for projectile, E = 0.5 * 0.01| * v^2 | Rearrange | (2 * 528) / 0.01 = v^2 | 105600 = v^2 | so velocity (v) = square root of (105600) = 325 metres per sec.

    That’s equivalent to a good black powder musket shot, so potentially lethal – if you don’t kill yourself first with the charged capacitors !!! http://en.wikipedia.org/wiki/Muzzle_velocity

    1. From the looks of it it generates as much bang, flash and smoke as a black powder musket when it fires. (c:

      I probably wouldn’t be trying this at home, but it’s still a pretty cool hack.

    2. Yeah, but those are some serious ideal numbers. I can’t tell if he’s using stainless or polished steel rods, but the conductivity is going to be less than perfect. Then there’s the coupling of the projectile to the rails.

      In the firearms world, 10g at 325 meters per second is a 154 grain bullet at 1066 feet per second. That’s about the equivalent of a .40 caliber handgun round. If it was really exiting at the velocity, I’d like to think there’d be some HUGE cautions about back-stops and not standing in front of it.

      I’d be surprised if it was making 30m/s coming out of that arrangement.

      1. I agree, I used the ideal scenario, wouldn’t want to stand in front though. It would have been nice seeing it firing at something, so we could see the damage. Perhaps ballistics gel, or something easier to get like a pumpkin. High voltage, danger of death, ballistics, smoke, sparks and wanton destruction – nice hack recipe :D

    3. First, I’d like to know where your 400V 2200uF capacitor in a car is, and what it is used for. I have no experience in this area, but I kind of doubt there’s such a cap in a car.
      Second, you are seriously calculating the kinetic energy with 100% efficiency?? Well engineered coilguns have about 5% eff. maximum! Railguns will be in a similar area.

  3. Just wondering:
    Since the resistance is pretty small, is the high voltage actually neccesary?
    Won’t this work with double-layer capacitors? (Got a bunch of 2,7V 360F lying around waiting to be used for something)

    (For those whining about the hazard of this build: Have you looked at the Hackaday logo lately? ;) )

  4. I am building this. Unfortunately, I am having some difficulty purchasing the capacitors. Anyone know a place with reasonable prices?

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