Let’s first take a look at how a railgun or magnetic accelerator works, a video about the whole topic can be found here.
Similar to a coilgun, a railgun works by magnetic propulsion.
A basic railgun consists of three parts: A set of parallel, metal rails, a huge powersource like a capacitorbank and a metal projectile. Here is a railgun’s schematic for your convenience.
What happens inside this small scale railgun experiment? There’s a huge current flowing through the rails and the projectile at the same time as shown in the illustration. Every current, or on a smaller scale, every moving charge creates a magnetic field. Take your right hand and form a fist – thumb in the current’s direction – your fingers now indicate the magnetic field lines created by the current in your thumb’s direction. Why is the projectile moving then?
According to Lorentz’s law, every charge (red current) moving in a magnetic (blue) field experiences a force (green).
So basically the magnetic field emitted by electrons travelling on the rails propels the projectile. Before we will take on real railguns let’s do a small scale experiment first.
These are two aluminum strips glued onto a piece of cardboard. Additionally I connected a 9V battery’s plus to one and minus to the other rail. Our small scale projectile is a metal stick with two small, round magnets on each end. The magnets are just here to amplify the effect and can be ignored right now – the experiment also works without the magnets as you can see in the video above.
Drop the projectile touching both rails and it will start accelerating towards the end of the rails.
What does this small scale experiment reveal about railguns’ physics? First of all you can see sparks flying deteriorating the rails, just as in a real high power railgun. Secondly the projectile gets hot due to the current flowing through it and its electrical resistance – again a great similarity to the real deal.
And last but not least, the projectile has to enter the railgun with a initial velocity, because otherwise it would get welded into place not accelerate at all.
So what’s the plan for a small scale railgun experiment?
In order to achieve a high current through rails and projectile we need a huge, high amperage powersource: A capacitorbank. Since a railgun is basically a big short circuit, normal batteries and transformers wouldn’t work well due to their inability to provide enormous high current peaks. The best solution for this low cost, homescale railgun experiment is a capacitor bank. My capacitor bank consists of three 2200uF at 400V capacitors in parrallel:
Most capacitors already have threaded poles, which is very useful connecting many capacitors via metal sheets as you can see in the picture above.
The rail setup consists of two metal rails sandwiched in between to PMMA acrylic sheets. Since the rails experience a lot of force during an acceleration test, they have to be secured tightly with screws to the acrylic sheets. Here’s my setup before and after screwing it together:
Now I had to decide wether to connect the capacitor directly to the rails, creating a “hot rail” railgun design, or to use some kind of high current switch.
I chose to stick with a “hot rail” design for two reasons: Firstly I simply did not have any switch or semiconductor that would withstand such high currents. Of course there are switches and semiconductors which would, but they were way too expensive for a small scale experiment like this. The second reason was, that the projectile needed to enter the rails moving anyways, so there was no need for a switch. The projectile itself would connect the rails acting as switch.
So here you can see the “hot rail” design.
The next challenge was to find a mechanism which guides in the projectile with an initial velocity. Most professional railguns use compressed air but I came up with a much simpler and cheaper method – a spring loaded lever:
The mechanism works pretty straigth fordward. Once released the spring loaded lever pushes the projectile between the rails:
Let’s take a closer look at the projectile. It is made out of metal and I chose a V-shape so it would be able to bend at least a little bit and compensate small unevenness. A piece of aluminium foil should also work fine.
The last step is charging the capacitors with the help of a little 400V DC transformer. The complete setup can be seen here:
Here is a slow motion gif of an acelleration at 400V.
This is what the rails looked like after an accelleration test:
There’s a video with a lot of footage testing the railgun experiment, of course:
can yu pls make a schematic of your 400V dc charger and upload it?
what is there to ad you just hook up the transformer to the caps
Would like to see the schematic/parts used in your charger? Thanks.
What happens if you coat the rods with something so you get the magnetic field, but not short out the circuit?
Clearly you don't understand how transformers work. You can't simply hook a 9V battery to a 1:45 transformer and get 400V out.
I'm curious what your final velocity is. Have you chronographed it, or done any penetration tests with an aluminum can or cardboard?
No short circuit, no current. No current, no magnetic field. So the answer to you question is, "nothing happens."
what about loading the projectile with a small solenoid that's spring loaded?
Leave the "hot" rail, push a switch to activate the solenoid and "poof", dead rats all over the place.
Use "C" shaped metal rails for guidance making for a smaller barrel and making sure the projectile stay on course.
Didn't understand directions, got balls stuck in the toaster again.
In all seriousness though, great instructions. I'm currently working on integrating this design into an airsoft frame so it can be mobile, like your G36 Gauss rifle.
Hi how did you make the transformer that charged the capacitors?thx
where do you get capacitors rated at that high voltage/capacitance?
ebay has them for around 30-50 bucks a piece
Could you please give a more detailed video of how it is made and how it works
I also want to know a bit more about the wiring
Two wires from the capacitorbank to the rails
But what about the transformer
No, he used an inverter circuit. Is a circuit that can turn the DC ino AC current, which can be trasformed and after there is a rectifier made of a few diodes. Just because he didn't ell anything about the inverter it doesn't mean that he didn't make it. The simplest inerter I know is made out of two identical NPN transistors and two identical resistors and a centre tapped primary transformer. http://4.bp.blogspot.com/-Os_dFBvh6fk/URcIUTS-AgI/AAAAAAAAAi4/vV-KOxCav3Y/s1600/IMG_2283.JPG
what kind of rails and the armature you use..?
we are trying the same with aluminium, but they are getting melted when such a high current is allowed to flow. it creates a spark initially, but does not move forward.
i think there is some friction acting in these.. you haven't mention about the frictional force in this. this frictional force is creating a lot of errors for us. how this frictional force should be overcome.
Your spring trigger looks awesome, but how did you get the capacitors to fire at the exact moment that your spring did?
He didn't. Capacitors have already wired to the rails. So when spring fires, "bullet" comes in contact with those two rails, connects them. Current starts to flow, and the "bullet" accelerates.
Where can you get the capacitors? I havnt found any sites to order 400v 2200uf capacitors
I know nothing about electronics so apologies in advance for the stupid questions, but.
Why are the capacitors in parallel and not series? Does it effectively create a single 400v 6600μF capacitor? Also, does having them in parallel slightly delay the outright delivery of power to the rails?
Forgive me if these are the dumbest questions ever asked so far regarding this project, but like I said, I know nothing about electronics.
i didn't see where you get the magnetic field to act on the projectile in the video? how did you manage to have an mag field upward to act on the object?
it will give you a higher capacitance if you have the capacitor in parallel. in series the total capacitance is (1/Ceq) = (1/C1) + (1/C2) + (1/C3) + … + (1/Cn). while in parallel circuit, the total capacitance is just the total sum of all capacitor (Ceq = C1+C2+C3+.. + Cn)
I built a similar railgun that fires smaller projectiles (3mm steel BBs), but I can't avoid the projectile welding itself to the rails about halfway up. Does anyone have a solution to this?
high current running through the ball and the force of friction between the two surface could result in extreme high temperature. maybe you can try a bigger projectile? or have something that is thick and have high melting point carry your projectile, then stop the carrier at the end of the rail thus letting the projectile fly away freely
Maybe depleted uranium (just kidding, but extra points if you know why it's the best ammo). I think tungsten can be used, but i dont know if its useful cause i dont know the general price of it.
I have a few questions. 1: would this work if the rails were copper tubing? 2: were your capacitors charged to full (I cant find a 400v power supply)? 3: it looks like you charged your cpacitors with a 9v battery how?
Tons and tons of capacitor charging/DC to high voltage DC circuits out there… And yet, there you have the question : "can yu pls make a schematic of your 400V dc charger and upload it?"
Do your own goddamn research!
The MIG welder makes it easier to carry out metalworking, as it helps joining of different types of metal pieces in a quick and fast manner.
1. Think so 2. Yes they were! 3. Transformer from an flash circuit!
Try shooting the projectile between the rails with air pressure!
More energy, higher voltage, stronger metal than aluminium and shoot the projectile in with air pressure!
I only attach the transformer when charging and take it away afterwards!
I got them from an old flash circuit!
what velocity or power was achieved with this design using 3 capacitors?
How many does it take a increasing velocity?
higher voltage will do nothing, higher amperage will do, in formula of magnetic voltage dosnt count.
Where did you get the spring loaded lever
hey can you make a railgun with rifle model
put the capacitor on shoulder restand use metal scrap around the barrel to protect you face
if you dint understand what i mean it okay
you're probably melting the copper/zinc/lead bbs are usually made of
if you don't mind having a flechette gun, straight sections cut from wire hangers work. just make sure you file the ends smooth or they'll cut through the railgun housing.
Hey dude I love your railgun experiment，but when I planning to make my own one, I found a problem: metal can always be oxided and form a oxidation film or layer, if this happens on the surface of the rail, then the conductivity will be strongly reduced. So how can I solve this problem?
are flash circuit transformers available in market ? suggest
Instead of solid bar rails, is it possible to use conductive jacketed solenoids? So each rail would be a solenoid inside of a conductive jacket, and the far end of the jacket would be where the wire in the solenoid connected to it. Essentially making the beginning of the jacket (where the projectile first contacts it) the end of the wire. ? Would that still work?
is projectile made of gallium?
you can boost the magnetic field by having standard magnets on the outside of the metal rods, this should up the force produced with same amount of current. is simple and you can use standard magnets or if you want to go all out use nedynium magnets.
what you ahve to remember is that the larger the capacitor the slower the discharge, a bank of hundreds of smaller capacitors will discharge quicker giving a higher current, whereas one massive capacitor will discharge slower reducing the current. small capacitors from used disposable cameras with flashes are perfet for this.
How much did the capacitors cost and where did you get them?
hey, be nice to him. you are a genius dude for building this. but I have some questions. firstly, where did you get the capacitors? and where did you get the rails as well. for your next project, you should make a supreme guard system with a self-taking photo camera, twin airsoft pellet turrets for both angles, and a spring-out hidden obstacle that blocks the entrance that shocks you if you try to pass. perhaps a spike ball. thanks for the excellent tutorial on this piece of fine art you have crafted. you are so freaking smart.