Semi-Automatic Rail Gun Is A Laptop Killer

It’s huge, it’s unwieldy, and it takes 45 seconds to shoot all three rounds in its magazine. But it’s a legitimate semi-automatic railgun, and it’s pretty awesome.

Yes, it has its limits, but every new technology does, especially totally home-brew builds like this. The aptly named [NSA_listbot] has been putting a lot of work into his railgun, and this is but the most recent product of an iterative design cycle.

The principle is similar to other railguns we’ve featured before, which accelerate projectiles using rapidly pulsed electromagnets. The features list in the video below reads like a spec for a top-secret military project: field-augmented circular bore, 4.5kJ capacitor bank, and a custom Arduino Nano that’s hardened against the huge electromagnetic pulse (EMP) generated by the coils. But the interesting bits are in the mechanical design, which had to depart from standard firearms designs to handle the caseless 6 mm projectiles. The resulting receiver and magazines are entirely 3D printed. Although it packs a wallop, its cyclic rate of fire is painfully slow. We expect that’ll improve as battery and capacitor technology catches up, though.

Want to check out some more railgun builds? We’ve got them in spades — from one with $50,000 worth of caps to a wrist-mounted web-slinger.

[via r/DIY]

37 thoughts on “Semi-Automatic Rail Gun Is A Laptop Killer

        1. Sure, it’s not a precision instrument but my point was more that you’re still probably going to hit the target. Plenty of people shoot cylinders out of their shotguns to great affect out to a few 10’s of yards.

    1. A rail gun could use electromagnets, or even permanent magnets, if they were strong enough. While most railgun designs I see use effectively a single turn electromagnet with the projectile as part of the coil to generate the magnetic field the principles simply require a magnetic field at right angles to the current and rails. There’s nothing that really prevents this magnetic field from being generated by more turns than amps in it’s amp-turns, it just may not be useful or even practical.

      1. You are confusing a gauss gun (electromagnets) with a railgun (which only has a magnetic field between the rails and projectile (or armature behind the projectile). See the links above to understand the difference.

        1. There’s a sort of hybrid that surrounds the rails with a coil, usually made of alternating conducting and insulating washers, with slots cut for stepped connecting blocks to join the conductive washers into a continuous circuit. The projectile has a forward coil and a rearward coil. The projectile coils have contacts that project out the sides to touch a pair of linear rails.

          Apply power, kick the projectile into the middle and off it goes. Arcing does wear the rails. Induction can be used to power the projectile coils, at a cost in efficiency.

          That’s the only magnetic gun design I can see any ‘easy’ way to provide a form of rifling. Bend the contact rails into a pair of low pitch helices and have guide grooves in the projectiles. Have the contact rails bonded to an insulating sleeve so they can be replaced easily by pulling the assembly.

          1. perhaps it is time to update the Wikipedia page! The danger is that people are already believing everything on these kind of website ans stop to investigate further or stop thinking themselves completely.
            Because… hey… I’ve read it on Wikipedia and therefore it must be true

          2. I was wrong on the name (and wikipedia is correct!) however can’t remember what the type of design above is called.

            There’s several reasons why external magnets aren’t popular though including that a reasonably high-power railgun will demagnetize close-by “permanent” magnets. And at best it can only reduce the real problem of railgun design slightly – the rails will wear quickly even with a reduced projectile current.

        2. What I’m talking about is perpendicular to that.. A railgun is just a hall-effect based projectile thrower with force on the armature being current through the armature cross magnetic field through the armature. Since I is pretty high and the armature completes a circuit it generates it’s own magnetic field going the right direction that’s pretty intense. The result being order I squared (I think?) so improving I is obviously good. That said, assuming there’s some practical limits to how high you can get I especially with all the arcing and crap you could just improve the magnetic field directly.

          I can think of two designs off the top of my head: First is the ridiculous row of donuts. You have an array of toroids or hallbach arrays with the rails running through the slits. These provide an additional magnetic field from a different supply using more turns and less current. The second design is basically pack of extra rails bridged at the barrel end and connected in series with eachother (and probably the rails) above and below the rails. This forms a squashed/stretched electromagnet again with the rails right in the center, this time more compatible with the power being supplied to the rails. It would probably look less ridiculous than the donuts too.

  1. I think y’all are confusing railguns and coil guns again. This is a rail gun. It doesn’t use pulsed electromagnetic coils. The “railgun” you featured before is a coil gun. Totally different principle.

  2. “its cyclic rate of fire is painfully slow. We expect that’ll improve as battery and capacitor technology catches up, though.”

    Nope, has nothing to do with the capacitors, it is all on the charger and power source.

    Seriously, does HaD make it a point to hire writers that have no clue what they are writing about?

    1. Yes. This is exactly what HAD does. BTW, if you are interested, we HAD is also starting a sister website focused on textiles and self-made garmets. If you are interested we’d like you to do a short piece on cross stitching for the general public.

        1. No, just don’t use all caps at once. Like you don’t fire all the explosives in the magazine at once. Modern power electronica may make it possible to stop the discharge (GTO SCR), but I am not sure.

          1. Either way your charging system is going to limit your ultimate firing rate.

            He would be better off building a backpack with a couple hundred 18650s in series-parallel to get ~360v to charge the caps quickly. You could probably get them wholesale for not a terrible price.

          2. Interesting that you mention GTO SCRs as not many people know about them. In this railgun, all the capacitors are discharged all at once, but that’s not the optimal way to do it. What you really want is a pulse forming network (PFN) which could consist of regular SCR’s, IGBTs or GTO’s, and that network discharges the capacitors one by one as the projectile travels down the rails. As one capacitor discharges, the next one is connected in parallel through the PFN. You could in theory stop the discharge, but why shut it down early when there’s still energy left in the caps?

  3. This is an interesting project. Something to consider for future video’s showing off electronics.
    These PCB design show no real competence in electrical engineering.
    Showing off these PCB’s in your video shows you just don’t care.

  4. From what I’m seeing, all he has is a co2 powered bb gun with a giant capacitor bank to make pretty sparks. I’ve seen that crazy German dude on youtube cause more damage to a cantaloupe with a slingshot.

      1. Probably. Don’t see why that would be relevant though. A high powered air rifle can easily kill people, even the normal playthings can if hitting the wrong spot under the wrong circumstances. IOW they can deliver significant energy to a target.

    1. Ask him to try the gun with only the injector active? I doubt the projectile will leave the barrel.

      Any working railgun will need a strong injection mechanism as otherwise the projectile will enter the barrel too slow and probably be welded in place before entering entirely.

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