I love to build dangerous things, as long as they don't cause any real damage. I probably shouldn't build dangerous things, considering the world seems to have plenty of those already, but I do. And in this instructable, I'm going to show you how to make a coil gun.
I should clarify: I love to build dangerous things, I don't like to do dangerous things. I also don't like to cause any sort of harm ever. So I guess I'm not crazy after all. One thing is certain, I'm crazy enough to build a device that uses high voltage and intense magnetic fields to make bits of metal fly through the air at high speeds.
In this instructable, I'm going to show you how I used an old disposable film camera and some wire to make a coil gun. Yes, a coil gun. (A magnetic linear accelerator if you prefer the technical terms)
Be sure to take a look at the video above for some build footage and a nice demonstration.
Before we begin:
-this project uses high voltage, high voltage is dangerous. take appropriate precautions
-this project is likely to result in a device that can fling bits of metal at high speeds, flying metal can be dangerous
-you may have the opportunity to make the resulting project look (and act) like an actual firearm. I do not recommend you do that. I much prefer making it look like some sort of homemade sci-fi weapon anyway.
-You must take full responsibility for your actions in creating and using this device. If you shock yourself on the capacitor, it is not my fault. If you shoot a hole in the wall, that's your problem. You've been warned. If you injure yourself or anyone/anything else, it is your responsibility and I am not at fault. Please use common sense and good judgement around devices like this.
Let's get started!
See it in action here: https://youtu.be/8aoER3hhNpM
Step 1: Physics
Before you dive in to this project, we need to talk physics.
Hopefully, you are familiar with the concept of a linear accelerator. If not, google it. I'm not great at explaining things like this in a large block of text, but I'll give it a shot:
It works something like this: imagine you have a magnet that disintegrates whenever metal touches it. Imagine you put a paperclip next to it. The paperclip would glide toward the magnet and then poof! no more magnet. But the momentum of the paperclip would force it to keep going, at least a short distance. If you have any experience with magnets, you probably know what I'm talking about. If not, go play with magnets for a few minutes and then come back. You'll see very quickly that it's not very complicated.
Alright great, now we understand that we need a magnet that can pop in and out of existence at will. How the hell do we make one of those? Well, quite a while ago physicists discovered that electricity and magnetism were really two forms of the same thing, and that a magnetic field will form perpendicular to the flow of electricity. So a bunch of parallel wires would form a strong magnetic field when power is applied. What about one long wire that runs parallel to itself? Well, that's basically a coil. So we can apply power to a coil to make it generate a magnetic field, and if we leave the coil hollow then stuff can pass through it.
Hopefully this is starting to make sense.
But if we want to make metal fly than we are going to need a really strong magnetic field. Well, more power is always an option. But more power usually means more heat and we would need thicker wire and all that. But all we need is a short burst of high voltage! Capacitors can do just that. And rather than design a complicated charge circuit and buy a beefy high-voltage capacitor, we can just salvage one from an old disposable film camera. The high-voltage circuits in disposable cameras powered the flash lamps, which run on about 330 volts. Perfect for our project, but also slightly dangerous. So be careful.
Step 2: Gather the Supplies
Some of the stuff you'll need for this project:
- a disposable film camera, from this you will salvage the charging circuit and capacitor (consult the video above if you aren't sure how to disassemble the camera)
- a coil, or enough wire to make a coil. I used a coil that I salvaged from an old doorbell mechanism
- at least two or three switches, you can add extras for safety
-this list does not contain the parts necessary to build an enclosure, I am leaving that part up to you. You'll also need batteries. Most disposable cameras used 1.5 volt AAA batteries.
- a sharpie or other permanent marker (optional)
- a soldering iron
- a screwdriver or two (these will be used to test the circuit and discharge the capacitor)
- electrical tape
- experience and a working knowledge of electronics is recommended, this isn't really a beginner project
- common sense (required)
- patience (optional)
Start by dismantling the camera to get what you need. If you aren't sure how to do that safely, take a look at the video above. It's long, low-quality, and kinda boring, but you might learn something from it.
CAUTION: The high-voltage capacitor is likely to be charged. Identify the contacts, usually near the flash bulb, and short them out with a screwdriver before continuing. It will likely make a huge spark and a loud bang. Prepare accordingly. DO NOT TOUCH A CHARGED CAPACITOR WITH YOUR BARE HANDS. YOU WILL RECEIVE A MASSIVE SHOCK. YOU HAVE BEEN WARNED!
Step 3: Start Soldering
When you have acquired the camera flash charge circuit, you'll need to locate and identify a few things:
- the capacitor. Hopefully you have already found this and discharged it across a screwdriver. If you haven't, do that now. right now. (the capacitor is the big deadly cylinder thing)
- the flash bulb. this should be obvious
- the charge button/switch. usually these are mounted straight to the board in the form of a little copper clip. When the circuit is powered, it should squeal softly when poked with a screwdriver. (This is just the sound of the capacitors being charged by the transformer circuit)
- the trigger switch. this is usually mounted on the side of the board and comes in the form of two thin copper strips. They should be springy and bend easily.
Once you have identified all of these things, you may test the circuit by plugging in the battery, holding down the charge button with a screwdriver, and then flicking the trigger switch. This should cause the bulb to flash. If it doesn't work, your circuit board may have been broken in the process of disassembling the camera :(
When you are sure that everything works as is, you'll need to take a few things off the board.
- de-solder the capacitor (or just use wire cutters if the leads are long enough) and save it for later
- remove the flash lamp. (in the process of removing mine, I messed up some of the trigger switch circuitry, but the project still worked. more on this later)
Great. Once you've taken a perfectly good thing and ripped it apart in the name of science, you'll know that it's time to start soldering. Solder a pair of wires to the places where the capacitor and flash lamp used to be, and be sure not to get any of these mixed up. Solder wires to the battery holder (optional) and the trigger switch. You may want to cover some of these connections in electrical tape or heat-shrink tubing to insulate them. Exposed wires can cause serious trouble.
Step 4: Build the Capacitor Bank
I happened to have an extra high-voltage capacitor from a previous flash-circuit project that didn't work, so I decided to combine the two capacitors to make a capacitor bank. Adding more capacitors does make the final coil gun more powerful, but remember that the capacitors have to be wired in parallel.
I soldered mine to a small circuit board and left plenty of room to expand and add more capacitors. If you only have one capacitor, solder a pair of wires to it (pay attention to polarity!) and then solder those wires right back to the circuit board where the capacitor used to be. It's as if you never removed it. That step is a little stupid, now that I think about it, unless you have a bunch of capacitors and plan on making a capacitor bank.
Make sure the capacitors are discharged and the polarity is correct. Unplanned discharges of high voltage are not fun.
Step 5: Attach the Switch and Coil
I mentioned earlier that I messed up the trigger switch circuitry when I removed the flash bulb. I was planning on wiring the coil in place of the flash bulb, but I came up with a new solution to that problem (see schematic)
Basically, I was going to wire the coil straight to the capacitor bank with a switch in between. When the capacitors were charged, I would just flip the switch and short them out across the coil. Foolproof!
Make sure the switch is:
- well-insulated, as it will be carrying pulses of high-voltage
- able to take the heat (not literally, but it should be rated for at least your common household voltage and current [120 volts at 15 amps minimum])
I used an old light switch, the kind you usually find mounted on the wall. These can usually handle the brute force of the capacitor discharge.
The coil should be a few hundred windings of kinda thin copper wire. Measure the resistance with a digital multi-meter, if the coil is more than 10 ohms, it might cause trouble. Thinner wire will have higher resistance.
Instead of winding my own, I just used one that I pulled out of an old doorbell mechanism. It is a little thin, but it works just fine as a proof-of-concept.
Solder everything together, wrap the connections in electrical tape, and test it. Place a paper clip inside the coil and insert the battery in the circuit. It should make a soft humming sound that climbs in pitch as the capacitor charges. Flip the switch to discharge into the coil. If the paper clip jumps, you'll know everything is working. Remove the battery and flip the switch one more time just to make sure everything is discharged. I added a recording of the sounds the circuit makes in action. See the audio file above if you are curious.
Congratulations, you have finished the electronic portion of this project!
Step 6: Build an Enclosure or Frame
Rather than walk you through the various steps of putting this thing in a box or taping it to a PVC pipe or whatever, I'm gonna let you design your own enclosure. I have seen many variations of this project that end up as boxes with switches on them. And while this is probably the most practical (and the safest) I had to do something different.
I cut a piece of wood into a parallelogram and glued/screwed everything to the top, with the switch on the bottom. I used a piece of scrap CPVC pipe as a handle, and glued that to the bottom as well. For the barrel, I rolled oup a piece of paper into a thick tube and slid it into the center of the coil. With minimal careful planning and little effort, I managed to create a sci-fi style handheld coil gun. It might pass as a prop for a low-budget sci-fi movie. (a very low-budget sci-fi movie).
Once you are done adding the finishing touches, it's time to give it a shot.
Step 7: Test Fire
[it might be a good idea to wear safety glasses and take some basic precautions]
I think I explained this earlier but let's recap: Here's how to fire it.
You'll need some ammunition. I cut the heads off of some nails and used those. If your projectiles are too heavy, they aren't likely to leave the barrel. Also, if they aren't magnetic (made of aluminum or plutonium or whatever)
- Load the coil gun with your ammunition of choice (paperclips will work in a pinch)
- put the battery in the battery holder, the circuit should make a little noise
- wait 20 seconds or so for the capacitors to fully charge.
- take aim and flip the switch
- flip the switch back to allow the capacitors to re-charge
When you are done, remove the battery and flip the switch to empty the capacitors.
Remember to use common sense! You are responsible for your actions!
Step 8: Going Furthur
This project was really a proof-of-concept. It isn't very powerful, but it can be scaled up by adding more capacitors and an improved charging circuit.
Though I will most likely move on to other projects, I encourage those with a little more electronics expertise to experiment with this design.
Ideas for improvement:
- magnetized ammunition
- more capacitors
- more voltage? (bigger capacitors)
- better charging circuit
- better coil
- general improvements everywhere
Let me know in the comments below if you build this, and be sure show off any improvements to this design!
I hope you enjoyed this project and learned something new! Remember to click the Vote button!
Best of luck, stay safe, and have fun!