Tuesday, March 22, 2011

tutorial: Coil gun

I decided to put up a tutorial to build a coil gun.
You can read the basics at Wikipedia. Its basically one or more coils accelerating a bullet via a strong magnetic field triggered in the correct timing. There are two different core designs to build a coil gun:
a) multistage coil gun
This means, there are more coils to get the projectile forward. The problem behind this is that you have to time the coils so that the ones behind the projectile are off while the ones in front of it need to be turned on. This requires you to build up some kind of circuit which triggers the coils. However, the potential behind this is that you can accelerate the projectile much better and accurater, resulting in a higher fire power.

b) single stage coil gun
So, the alternative to the multi stage is a coil gun which just uses one coil, turned on with a high current flowing and let it be off before the projectile is through. It results in a much more inaccurate acceleration, giving less potential firepower. However, its a much simpler design requiring nearly no extra circuits.

This tutorial will yet cover only the basics of a single-stage coil gun, and as soon as my multi-stage coil gun is working fine, I will post a tutorial to build it.
So, here is what we need:
a) A capacitor. You need an electrolyte capacitor. They have two important measures: The  voltage and the capacity. You'd like some with a decent high voltage and a middle-high capacity. The formula for the energy contained in a capacitor is E = 1/2 C U ², which means, if you double the voltage, you get a four times higher energy. If you double the capacity, you get the double energy. So guess what, you try to get the highest voltage possible. However, I recommend to not exceed 100 Volt for newbs and for nerds I recommend to not exceed 330V (Why this? It means you can still charge it on a regular plug. Ofc, if you have a 110 Volt plug, you'd not want to exceed 160V. Don't get why 160 Volt for a 110 Volt plug? Its the peak voltage). The more Voltage, the more dangerous it is if you touch it. Then, you do not wan't to have an exceedingly high capacity because that mean's it'll take too long to let the capacitor run empty, resulting in a possible pull back effect for the projectile. Get what I'm saying? The projectile runs through the coil. Now, if the coil is not turned off by the time the projectile is through, it will pull the projectile back. You would not want that. (Moreover, a high capacity may cause a short in the batteries because its basically no resistance at the beginning of the charging process)
For my first coil gun which ofc was just built in 3 hours and was maybe as strong as a decent softair, I had a capacitor with 25000 microF and 100 V (charged to just 90V). You can get capacitors from the internet of course, or you visit some kind of speaker shop. I got mine from that speaker nerd around the corner, I just asked him if he had some capacitors left. Worked fine.

b) a voltage source
You'll need something matching your capacitor's voltage. So, as my first capacitor had 100V, I had 10 9-Volt blocks which means it did charge with 90V (yeah it was just for aestethic reasons not 11 blocks with 99V). Well, you can calculate how long the batteries will last.  Let's say you got 600 mAh, this means 600 mA one hour long at 9V. So, this is 0.6*9*3600 ~ 19 kJ of energy. My capacitor with 25000 micF and 90V (charged) contains 1/2CU²=101 J of energy per shot, so it will last around 190 shots. It's enough.
Now, I better don't tell you how I charged my second coil gun, because it's too dangerous. It involves a glass of water, some salt, some wires and a plug with 230V (and a bridge rectifier).

c) A coil
 Well, this basically means a lot of wire with a thin isolating layer to prevent shorts. I did the coils myself, so I went to the speaker nerd guy and asked him about old coils. He gave me alot with 1-3mm thick wire. Basically you just spin it around the barrel as long as you want the coil to be, and then you add the next layer right away. You have to watch out to keep the same direction all the time, otherwise your coil will be useless. Don't worry, the coil will look a bit shitty, but it's alright though. However, try to keep the first 1-2 layers as clean as possible. The coil shouldn't be too long, this will make the magnetic field too low. However, having the coil too short is worse because it may pull the projectile back in and moreover, its harder to spin a shorter coil.

d) a barrel
you should use some massive plastic or aluminum here. Really no iron or steel, because it's magnetic and will make the magnetic field veeerrry, very slow, unable to shoot a projectile. I used some thin plastic barrel.
You have to spin the coil around it.

So, what you actually do is (I will not explain how exactly you do this very well, because that depends on your favors):
You take the capacitor and attach it to the voltage source for a few seconds (batteries should do the trick under 15 seconds normally). You then put a projectile 1-4 cm before the coil and in a single clean strike attach the capacitor to the coil. Beware, you need to seperate it from the batteries before to not cause a short.
The result is a strong magnetic field. Why? Well, if your wire has a resistance of 0.05-2 Ohm, which is realistic (since its just a wire, probably even pretty thick), and you attach a voltage of (for example) 90 Volt to it, you have a current of 1800-45 Ampere. Well, I had like 300 probably at the peak. This is really high.

 PS: Watch out to not make the coil wire too long, a high inductivity will lead to slow magnetic buildup times.

And since you all don't care and I wouldn't either, here are some Videos of such guns to satisfy your real needs ;)

 Nice made coil gun, not too strong though.

Decent one as well, especially it's pretty strong for the energy I feel.

 Very strong, but for the energy and the SCR triggering (it's a multistage) not that high.

Really weird rail gun, makes a huge EMP as well. Neat!

The navy researches as well:

So far, thanks for ignoring the upper part of that posting. I'll provide some images of my 680J Coil gun the next days as well, at least it pierces 1.5 mm steel. That's tough isn't it? ;)


  1. Making something like that would scare me, I would surely kill myself.

  2. looks so kewl...but dangerous indeed

  3. make a video of your own coild gun.

  4. this is awesome I want one too

  5. Really bad idea! haha! How well!

  6. those things can take an eye out!
    i like it...

  7. That's an interesting concept... more interesting than practical I wager, otherwise the military would use them hehe

  8. I've always wanted to build a coilgun. I've got a decent capacitor bank rigged up, I just haven't got round to it.

  9. Is this what engineers do all day?

    I should build one of these.

  10. Oh railguns, they are just so awesome. I really hope this is the technology of all weapons in the future, because they are just plain awesome.

  11. Its pretty neat, but it seems impractical.

  12. awesome that is so cool. thanks for the tutorials. did you study physics or something?

  13. awesome guns, i would really like to see your coilgun in action

  14. Dude, wouldn't it be awesome if we could arm our military with these?