# 400 Volt RAIL GUN

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For this instructable I will explain how to make a simple rail gun, firing metal ballbearings. However, the parts are not to expensive, but im not sure of how much it all came to as I built it at my school during DT lessons. There are more powerful versions, but this doesn't take long to build and is quite effective.
It is not very neat, but I didn't have much time as it was only meant to be an alternative way of building an airsoft gun using a new system (part of my GCSE project). My design fired 9mm steel ball bearings, which is fun, but can cause injury.
This does use voltages upto 400V, and comnpressed air, so be carefull, and never put anyone at risk from whatever you manage to create.

The railgun is a form of linear accelerator, using a electromagnetic force to propell an object. The way that these work is that a electrical current is conducted up one rail, across the projectile, and then back down the other rail (see picture). This is called the Lorenz force.

This is my first instrucatble, so please be nice...

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## Step 1: Parts

Most of this project can be changed, so you don't have to use these exact parts, but these are what I used for mine.

For the Compressed air system;                                                         (step 4)
Gas reservoir- I used 4 small one, but a large single would be perfect, or use a spring.
2 gas valves- 2 gives a faster rate of flow, but not necessary if using a spring.
Pneumatics pipes- reservoir to valve to barrel connections
Steel tube (barrel)- diameter must be similar but slightly larger than you projectile.

For electrical (the rail gun)
I used 10 400 volt 450uf aluminium electrolyte capacitors (step 2)
Solid aluminium bar (for rails)- 20cm x 3cm x 3cm              (step 3)
Acrylic 20cm x 3cm x 0.2cm

## Step 2: The Capacitors

For my design, I used 8, 400V, 470uf capacitors connected in parrallel. This gives a total capacitance of 3600uf, but still at 400 volts. However, charging them off a 9 volt battery will only give you 9 volts output. To charge these to 400 volts, you can use two different methods.

You can do the more dangerous way (don't unless you actually do know exactly what your doing) of putting the correct step-up transformer into a plug socket and then adding a semi-conductor diode
[Capacitors must be charged using DC current, not AC, aluminium electrolite capacitors can only be charged in one direction, else they can heatup, melt, or explode].

I would not really recommend going anywhere near the mains and sticking stuff in, so the best option is to build, or even better, buy a DC/AC converter (there are lots of small car converters you can buy that run on 12v batteries), and then connect a transformer to the output, and add a semi-conductor diode to change it back to DC power. This is probably the cheapest and easyest option.

You can also use the flash circuit from disposable cameras, but to charge 8 capacitors of this size, I would need quite a few or risk burning the circuit, and disposable cameras aren't that cheap and shops now send them off somewhere after use, so I couldn't get any used ones.

## Step 3: Rails

The usual way is to use two parrellel metal strips, with a gap just large enough for your projectile. However, this provides a poor connection area between your projectil and rail, and can cause more sparks and therefore faster errosion to your rails. My design used a solid aluminium bars about 20cm x 3cm x 1.5cm.

I clamped these togeather, with a sheet of perspex between the two. Then, I drilled down the center of the two blocks and perspex, with a drill bit slightly larger than my projectile, forming a abrrel with two metal sides with a plastic insulation between the two. I did this 3 times, and the put the three sections togeather to form one long barrel/rail.

Aluminium was probably not a very good choice in material as it is quite soft (compared to steel), and can be damaged easily by any sparks made, with effects the connection between the rail and projectile for the next shot, but it was the easyist metal to work with.

Connect the capacitors, the positive terminal to one rail, negative to the other.

## Step 4: Pneumatics

The metal projectile cannot simply be inserted into the rails, as you'll get electrocuted, and the projectile will get spot welded onto the the rails by the large electrical charge suddenly jumping across the projectile.

To prevent both of these things happening, the projectile must already be moving befor it meets the rails at a sufficient speed to prevent it stopping. My system used 4 small gas reservoirs (you can use one, but these were all i had at the time, and my other large cylinder was attached to another project). I charged mine to around 120PSI, but the amount of pressure you need depends on the weight of your projectile. I didn't need such a high pressure, but it was more fun this way.

You don't have to used compressed air, but this was the quickest and easyest way for me as I only had to put the components togeather instead of build any parts.

You simply need to connect  your cylinder to a valve, and then the valve to the barrel (this valve also acts as the trigger) and some way of refilling your cylinder (another valve connected to an aircompressor or foot pump), and a plastic barrel that is a tight fit with your projectile. The end of your barrel should feed directly into the rails.

You can add some sort of breach, but as this was a prototype for my main GCSE project (an airsoft gun) I only needed proof of concept, so didn't have enough time to bother with one.

## Step 5: Final

Put it all togeather, and you should have a working (or not) railgun. Don't point it at anyone, and discharged the capacitors befor handling after each shot as they don't always full discharge. Just place a screwdriver over the rails to complete the circuit as the projectile would have done. Also, after charging the capacitors, you must disconnect them from the charger as they will discharge back into the transformer. This isn't really a problem except you will loose power befor you shoot.

My video is only using 30volts, because at that point I did not have a DC/AC converter, but the result is still quite good, with some nice sparks coming from the end of the rails, and the person who does the "Oh my..." is not me, just a friend watching.

I actually now have 10 400 volt 480uf capacitors (I forgot about the last two). This, when charged to 400 volts, produces 360 joules of energy, which is capable (excluding resistance, friction, all the other stuff) of 1011.26 m/s, but as this is actually a very inefficient design, the actual velocity will be a lot less.

I now have a inverter, but having a few problem as the voltage output is over 2000 volts, and AC, so i'm trying to get a transformer to lower it to 400 volts, and buy a rectifier diode to convert it back to DC.but it will be mounted to my actual GCSE project (an airsoft gun) so will use new rails and a 6mm copper-coated airsoft BB. Unfortunately, this means the video won't be ready untill some time after easter hols.

## Step 6: New Project

My GCSE project has finally been finished, but not tested as the physics department wouldn't let me use thier 400 volt power supply to test it with (for the capacitors) and i'm still working on my DC/DC inverter. However, it is made for airsoft (but it has to use 6mm steel ballbearings. It works the same way as the prototype (the railgun described earlier), but with a loading mechanism and a better compressed air system, making it a bolt action sniper.
This will be my next instructable, but will take a long time to make, as the total parts are around 70, plus the pneumatic and electric circuits (very simple).

Unfortunately, i'm not sure if i'll ever be able to test my project as my physics department has a power supply that goes to 400 volts, but are worried about safety, ethics, legality... but i'll ever get my DC/AC inverter and do it that way, or use cameras.

The pictures I have uploaded of my airsoft gun are old, as it fell off the shelf 2 weeks befor being marked (hitting a computer, edge of table and the arm of a chair) so had to be completely rebuilt, but most of the individual parts weren't to damaged, but it looks slightly different, and better now, and has a bi-pod attached to it, unfortunately all the photos are still on the school's computer, and i'm now on holiday, so they won't be up for a while.

## Step 7: Next Project

For my A2, i'm hoping to change the coil gun/ rail gun idea and mix it with some ideas from the particle colliders. I will be making an oval section of tubing, about a metre long, and wrapping the entire thing in 8swg enamelled copper wire (if i can find enough). This will be done in about 10 sections, so if one melts, then I don't have to replace the entire lot. These will be connected to 40 amp continuous dc power supplies, with a ball bearing inside the tubes. Then, playing with about 10 different capacitor packs and light gates, I hope to be able to get the ball bearing (always hopeful) to 340m/s, the speed of sound! Hopefully, the physics department will be more supportive of this project and help me with the power supplies. Then, the tubing will be surrounded in a shell of aero-gel, and providing the physics department like my project, filled with CO2 (not liquid as it turns from solid to gas almost instantly) to about -78 C. There will also be a small gap either side of the oval so you can see inside the tube, and so the light gate can measure the speed. So, if its built well, wrapped with 3 layers of copper (a total of about  50m of wire), cooled sufficiently, and the right amount of power used, it should be attainable. If not, it'll look awesome anyway. But, that'll take another year, and won't truly be started until after the summer.

More to follow...... after exams!! yay

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## 62 Discussions

Theoretically, yes. However, you will only be getting 1/2 to 1/3 the power, which may not be enough to drive your projectile.

No, not nearly enough power. Use this to see how many joules of power the capacitor holds: http://www.electronics2000.co.uk/calc/capacitor-ch...

Unless you broke physics, your efficiency is going to be terrible (I've been calculating .5% in my design), so you need a lot of energy to start with. You also need enough voltage to make a good arc, so you probably need something at least in the 300v range.

a cool idea would be a farnsworth fusor but there really expensive if you want actual results

hey if the projectile does not move try to hook up capacitors in parallel, so you get more microfarads. not in series.

how about a marx generator? or am i crazy?

Hi....

I already trying to build one. But when i'm firing it, the ball bearing was not sped like your's.

In my design, i use two parallel aluminium strip and the gap between 2 rails is 2.1 cm and the diameter of the ball bearing is 2 cm. so,what i want to know is, does the ball bearing and the rail need to touch each other when it is fired ??

Thanks !!

2 replies

So I made a rail gun last year for science fair and when I made it I used .25 steel balls. the distance between my rails was .252 .

Preferably, yes, they need to touch, other it might not get a constant current flowing through, and there will be more arching, which will erode your rails faster and result in even less contact. It should work without them touching, as long as the current can jump the gaps, but probably not as well.

Oh my... Yes, this helped me so much. I am currently in the process of building a railgun similar to yours, but on a larger scale, and I needed help with a lot heading into this project, but this guide really helped me and it shown some important problems that I haven't put any thought into yet. Currently, I am cutting aircraft grade aluminum I received as a donation, and planning how I'm going to insert the capacitors into the back,, and basically, it's really tough stuff. So I'd like to thank you for the help on this, it's nice to know someone did something similar to us.

(unfortunately, I don't have images yet, but I'll be sure to show you in the comments once I do!)

you could use diodes for the problem of energy going back into the transformer issue you mentioned.

2 replies

You kidding me? Pneumatics?
You could make a regular spring magazine so every shot it will reload automatically(unlike in regular ARs, which require the gas to push the bolt back).

You kidding me? Pneumatics?
You could make a regular spring magazine so every shot it will reload automatically(unlike in regular ARs, which require the gas to push the bolt back).

The answer is... a paintball gun.

crazyjp got me thinking though... If you use the paintball gun as the initial means of propulsion and then build a rail gun around it, would it work? Like a "sleeve" that you bolt in place over the barrel with all the caps and wiring built in, all you will then need to do is find a way to activate the circuit automatically once the paintball gun has fired. You might have to cut down the barrel though, the standard barrel should be okay since they're mostly quite short and useless anyway.

The loading problem has also then been solved as most paintball guns are semi-automatic and have hoppers attached, all you need is a the correct diameter projectiles.

You might need some kind of separate battery-pack or else things will get real heavy. Unless you can find some small, light, long-lasting, high-voltage batteries.

if your using compressed air wouldnt it be simpler top just take the compress air hose hook it up to a barrel that just barely lets your projectile slide through put a notch in the spot were you want to load the projectile adn get a piece of tube that will slide over the spot where you load the projectile ad have some type of triger that when pulled causes the compressed air to be shhot into the barrel forcing the projectile out the end of the barrel and just demolising what ever you were aiming at??? i mean sure making a rail gun would be bitchin but you would also have to deall with some type of power source that can create 400volts verse just an air tank you strap to your back and refill off of a 120 volt air compressor?? i dont know if im wrong when it comes to thinking that the gun would be lighter if its just powered off of compressed air than having a bunch of batterys and capaactiors and metal rails