No howto for the Railgun? This will be fun! =)

How to make a Railgun in 7 easy steps:

  1. Get a nuclear power station. This isn't completely necessary, in fact it's very much over kill. But access to a nuclear power station will ensure that you have a great power source
  2. Get two extremely powerful, extremely fine UV lasers and align them so that they're firing their beams parallel to each other and are separated by about 1mm. You'll probably want ot mount them in a box of some sort too. Make sure that the beams are hitting a VERY good insulater because they'll be carrying a huge current. What? Beams of light carrying current? Well, that's not really what's happening, but it'll do for our purposes. If you do mount the lasers in a box then drill a hole in between where the lasers meet the insulater at the end of the box. This is where our slugs will be coming out of the box at about 143 meters per second.
  3. Get two really strong magnets that are about 1m in length (about one tesla each would be good) and glue them to the top of your box above and below the lasers so that the north poles and south poles are facing (see picture below). You'll probably have to reinforce the box somehow because the slug will be exerting a HUGE (big, big, big) force on them. About 500N which is like supporting a 50kg person standing on them.
  4. Get some REALLY small ball bearings (diameter of about 1mm) and find some way to get them to fall EXACTLY in between those laser beams. After we have finished, the balls will hit the laser beams and accelerate at about 10,000 ms^-2 so it's pretty important that they fall into these beams at 90 degrees to the lasers, otherwise they'll hit something in the box and cause BIG damage
  5. Get some superconducting material of some sort...
  6. This superconducting material will carry the current from the power station to your laser beams. Of course we don't want the -ve and +ve electrodes to get too close (we're dealing with a potential difference of about 50,000 volts)...Now these electrodes need to supply the electricity to the laser beams so that the beams actually have a potential difference across them. But by doing this you cannot block the beams with the wires so make them thin.
  7. GET OUT OF THE WAY OF THE GUN, flick the switch and aim it towards the sky. You can drop a ball bearing into the beams and know that you have a working railgun!




                |                             |
  _       - ===== - - - - - - - - - - - - - - #
  | 1mm         |          O                     ->
  -       + =====- - - - - - - - - - - - - - -#

                |          Magnet              |
                | N     N      N     N     N   |
           +     ------------------------------     O  ->
                | S     S      S     S     S   |

It's really important to get the poles of the magnets and the electrodes right otherwise you'll probably end up with another oriface in your body.

How does this work?

Unless people want me to, I won't go into the deal with the UV laser...
When the ball bearing drops into the lasers, it is closing a circuit and thus carrying a current. There are technicalities involved due to the UV laser stuff, but I won't go into that. Anyways, the ball is therefore carrying a charge and accelerates due to a Lorentz force created between the magnets and the ball. This is why the magnets need reinforcement. I worked it out to require a potential difference of about 50,000 volts across the lasers* and a 2 tesla magnetic field. This will supply a force of 500 newtons and the ball, weighing about .0005 grams will accelerate at about 10,000 ms^-2. This acceleration lasts for a fraction of a second, though, which means that the bearing comes out with a speed of about 500kph. This is pretty slow by railgun standards, but it'll be fine for our purposes. If you really want to kill someone then I'd suggest that you buy a real gun...

I don't suggest you try this at home. I imagine that it would be rather hard to try, but if you do have access to the parts required then DON'T try it still. You're dealing with some pretty deadly stuff here and I'd hate to lose a fellow noder to a homemade railgun experiment.

*Of course, you need to somehow find a way to prevent current leakage across the lasers.

/msg me if you want me to add/take something
Deadbolt says a railgun isn't a railgun unless it fires slugs made of depleted uranium :)

A more realistic homemade railgun

Short of obtaining a Nuclear power station, UV lasers, and a supply of superconducting materials, there actually is a way to make a home-made Railgun with just a few compromises. It will not (usually) kill or maim people, and isn't good for self-defense. There are better ways to defend yourself. This simple railgun, however, if we allow for the use of static magnets, rather than electromagnets, can be made mostly with materials you might find in your garage or around the house.



  • Space the magnets (M) about 5-7 cm / 2-3 inches along the ruler in the groove with a space at both ends, and tape them in place. Make sure the magnetic poles are oriented all in the same direction along the axis of the ruler
  • Place two ball bearings (O) on one side of each magnet. (The first ball-bearing spaces the second away from the magnet so that the magnet doesn't simply overcome the forces involved by holding on to the ball bearing)

(yes - I know it spells "Moo")

Now you have a simple but working railgun! To fire it, roll a ball-bearing toward the first magnet (on the opposite side from the other ball bearings), and don't stand in front. Reloading is as simple as replacing the ball bearings back in their original positions (you supply the potential energy here that is converted into kinetic energy.) Here's how the railgun works:

  1. The first ball-bearing rolls toward the first magnet, is accelerated by the magnet, and hits with velocity V1.
  2. The force of the impact is transmitted through the magnet and two ball bearings, causing the second one to shoot at the second magnet. It is also accelerated, and hits with a higher velocity V2.
  3. The cascade continues, each ball-bearing hitting with a higher velocity, transmitting greater energy through the magnet and first ball bearing, and imparting it to the second, until the last ball bearing shoots off the end of the railgun.

You are now ready to go out and attack some tissue paper or bananas. The effect at this point may or may not be underwhelming... so let's tune the sucker!

Tuning your Railgun

There are a couple of ways of tuning the railgun, so let's discuss each one.

Bigger and longer
Our military knows that the way to make weapons better is to make them bigger. In this case, you can use bigger magnets, and/or a longer base. Using bigger magnets works great, but remeber that with strong magnets you can wipe out you credit card, ruin your wristwatch, or pinch the living snot out of your finger (It takes two), so be careful!

Balancing distances
You can improve the performance of your railgun by increasing two distances: The distance of the ball bearing being "kicked" from the magnet, and the distance that ball bearing has to be accelerated by the following magnet.

You can increase the first space by inserting more ball bearings, or by using an iron rod (which transmits the force well and will hold the ball bearing magnetically).

The second space can be increased just by... well... increasing it. There are rapidly diminishing returns to both methods as the magnetic field falls off proportional to the cube of the distance, and friction begins to eat away at your railgun's efficiency.

The best method is, on a level surface, to increase the first distance by enough that the ball bearing is barely held in place by the magnet, then to gradually move the second magnet closer and closer until the ball bearing is pulled off, then back it up just slightly.

Other Considerations
There are very strong magnets to be had, and tuning the railgun correctly can result in some pretty significant velocities. This can result in damage to your magnets by chipping or even exploding, and the fragments can put out your eye. Depending on the magnet strength and your tuning prowess, you may wish to invest in leather gloves, wear eye protection, and refrain from pointing the business end of the railgun at breakable objects or people that you like. A great source for magnets and more information is If you can convince them you are an industrial concern, they may even show you The Good Stuff!

Thanks to Wingbat for showing me his prototype railgun, and for the cool cube magnets!

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