6mm Coil Gun


Introduction: 6mm Coil Gun

About: I build stuff because it isn't available to buy, or is too expensive, or the ones you can buy don't do what I want them to. Sometimes I don't have a reason, I just want to build something. For me it's about...

This is roughly as powerful a coil gun as you can make using a standard mains switch. To make a more powerful coil gun you will need a higher rated switch, preferably solid state.

Through much research I found all the Variables that affect the efficiency of a coil gun:

Length to diameter ratio
Initial Positioning
Flux Linkage

Number of layers
Thickness of wire
Flux linkage

Current Pulse length
Switch bounce and resistance
Capacitor Voltage and Capacitance
Overall wire length and diameter used.

Also there are several ways to increase standard performance using:
Optical, Inductive or Physical Triggering
Multiple stages
Super cooling

Step 1: The Plan

I had some 6mm steel bar, some 6mm plastic pipe, a micro switch and some enamel coated wire as a starting point.

I took apart 17 disposable cameras and soldered the capacitors in parallel to form a capacitor bank of 1360uF 330v which using E=1/2CV^2 gives a stored energy of 73J.

I used one of the camera circuits as a charging circuit by removing the flash, removing the trigger switch and soldering the charge switch closed.

I then used an old mains PSU switch as a charging switch although any switch will do. The whole circuit was covered thouroughly in insulation tape and put in the only plastic box of the right size I could find at the time; An empty Bertolli spread box.

I wrapped a coil out of 26AWG enamel coated wire 30mm long and 7 layers thick. This is because the coil should be the same length as the projectile and the projectile should be five times longer than it is wide, hence 5x6=30. The number of layers is dependant on wire thickness and capacitor bank size and voltage. The thinner the wire, the smaller the bank, the less layers. wire too thin will impede flow and maybe burn out. Wire too thick will mean you have less coil density than is potentially attainable.

Simulations ran well after the device was constructed reveal this isn't an optimal design and there is some 'suck back' as you can see on the graph when the turquoise line falls bellow the axis suddenly.

Step 2: The Coil

Find a tube that isn't made out of metal, with thin walls and that is a close fit for the prospective projectiles. Measure the interior diameter and multiply this by five, this will be your coil and projectile length. Measure this distance, for me 30mm, from the end of your tube and make a mark using a permanent marker. Measure another 30mm down and make another mark. Your coil will be wrapped in between these two points. Wrap some tape around the tube at these points to form flat sided ends to wrap your coil up to. These should be approximately the diameter of your projectile deep.

Get your enamel coated wire and tape it to the tape stopper at one end and start coiling the wire around the tube, when you reach the end use super glue to hold the first layer in place. When it has dried start coiling again, this time the coil will go back to the starting end over the top of the first layer and glue in place. Repeat this process for approximately 7 layers. When the coil is finished put on a layer of insulation tape and your done.

Step 3: The Circuit

The circuit is very simple. Take the Camera circuit and chop off the flash trigger "switch". It is usually two flimsy bits of copper that stick out of the circuit on one side.

Next solder the charge switch closed and add extension wires that you can solder onto your battery holder with an toggle switch. This is your charging switch and should be a switch over toggle so that one side is charge and the other is safety so that you can never fire it while the charge circuit is engaged. Doing so wouldn't damage the coil gun but it's good practice not to, especially when you upgrade to a mains powered coil gun. 

Remove the flash tube and capacitor taking care to remember the polarity. Solder in new wires from the circuit where the capacitor was previously connected.

Take your capacitors, essentially you want as many as possible and solder them in parallel so that all the negative legs are connected on a rail and all the positive legs are connected on a separate rail. Solder the wires from the charge circuit to the bank.

Solder on the two thickest wires you can find to go from the capacitor bank to the coil and insulate the whole circuit with heat shrink, insulation tape and hot melt glue. You do not want any chance that you may accidentally electrocute yourself. I will warn you now, it hurts... ALOT... and when you've got a bank of over 50J it can make you feel very ill. Not an enjoyable experience.

Solder in your push switch in line with the positive lead from the cap bank and then to the coil you just wrapped.

Put all this circuitry in a nice safe plastic box and your ready to go!

Step 4: The Projectiles

30mm sections cut out of 6" nails and other 6mm round ferrous rod I had lying around. As I didn't understand the principles at the time many different lengths and shapes where made and tested. I shaped them by putting the bar in an electric drill and using a file and various grades of sand paper to remove material.

I've done a separate Instructable on Projectile Design since it is such a big section.

Step 5: The Results

It works reasonably well! Using Vertical drop VUSAT equations and thorough testing I found that an optimum of 13m/s, 50KPH, 30MPH. Using KE=1/2MV^2 I found that the projectile had a maximum of 0.6J Kinetic energy. This was initially exciting but after realising some AirSoft guns are as much as 1J I was slight disappointed and decided to up scale as I had reached the limit of these components.

I've designed and built a 50 cal 217J Coilgun.



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    could you use high voltage microwave caps?

    Could one use a 100K uF 600V cap in place of the photo caps?

    how fast is that Ben?

    can you add a fly-back transformer from a tv instead

    I have 962 uf and 2640 v is that good?

    The energy stored in a capacitor is = 0.5*capacitance (Farads)*Voltage*Voltage. So for your Capacitor it would be 0.5*2100*2100*0.000001=2.205J. In comparison, the one in this Instructable is 73J. Having said this even 0.01J would accelerate something, it would just have to be very small, light and it wouldn't go very fast.

    Put simply: Yes it will work, but it will be pretty pathetic. Almost Certainly not worth doing. You would probably be better using a Car battery charger or an ATX powersupply or even some lipo batteries.

    I have one 400V 2.2uF capacitor but no camera circuit can i still make a coil gun

    1 reply

    Not really, you only have 0.362 J of energy which is less than 1.7% the power mine has. It wouldn't be very powerful... you can charge it using any dc voltage source. A rectified 12v to 230v inverter would charge it to roughly full voltage. This is dangerous though and I do not recommend it.

    Yes, but don't expect the power I have. You will have less than 1%. of that.

    Could I use your graph photos for a project? You will be credited and referred to.

    1 reply

    Of course. If you want me to plug your coil gun parameters into my simulator and make a graph for your coil gun then I can do that for you as well.

    Can you tell me were to get your stuff like the psu switch and the 6mm bar. I am having a hard time finding some.

    3 replies

    You can use large nails instead of the 6mm bar but that should be available at your local hardware store, I believe mine may have been left over from a guitar stand project I did a while back. If so I got it from B&Q. Focus and Do It All should also have some.

    The PSU switch is just a switch, any switch will do. Mine was out of an old computer power supply unit (PSU) I used to get broken ones free from the IT support department at the university. Your schools IT department may have one. If so be careful when dismantling as the have high voltage capacitors in them. If in doubt, consult a responsible adult and or chicken out. Better to not have the parts than be dead.

    On your circuit diagram I see this 'Reverse Voltage Protection Diode'. I am not sure what that is. You don't mention it in the textual instructions and I'm wondering if it is required.

    It isn't required but it is highly recommended. It is just a normal diode like you would use in a Wheatstone bridge to rectify mains AC into DC.

    The coil gun system is very similar to a transformer. When you dump all that electricity into the coil a massive magnetic field is generated around the coil which is was attracts the ferrous projectile into the coil. When the electricity runs out or the switch is broken, the magnetic field collapses and the projectile de-saturates. This is how a transformer works, The varying magnetic field induces a current in the coil. So when the field collapses a current is induced which can break your components such as capacitors by charging them backwards. The diode is there so that the electricity can go back into the coil and dissipate rather than frying your expensive caps and solid state switches.

    What is a microswitch and what type should i use. I dont see any information about the microswitch you used.

    1 reply

    Google is your friend; A microswitch is a small switch that is usually rated to mains voltage and relatively ample currents. Around 240v-12A. They aren't usually used directly but rather via a door, latch or cover. An example of one is here:


    then suggest me some effective charger for caps but not the disposable camera one thanks!

    1 reply

    Which country do you live in? or more importantly what voltage is your mains electricity? Assuming it is in the order of the 50Hz 240v RMS that we get in the UK you should be able to use half or full wave rectified mains electricity to charge them though I wouldn't recommend it as it is inherently dangerous.

    I would suggest you use a 12v to 240v inverter and a small battery as your power source rather than messing with the actual mains though as mains is incredibly dangerous as it happens to be at roughly the right AC frequency to stop your heart and there's an unlimited supply of it out of a socket.

    You should use half wave rectification to limit the power available and put a reasonably large charge resistor in the way to stop the cap charging too quickly. I have used a standard 40W bayonet light bulb for that previously because it offers non-linear charge resistance. Make sure it's all in a double insulated box and you need a tool to open it. No metal touchable on the outside etc. Check my 50cal for instructions. That is the charge circuit I used on it.