Do It Yourself Homemade Railgun

Do It Yourself Gadgets ^ | Friday, October 4, 2013 | Ameres Valentin

[Utilizer]

Homemade Railgun Experiment Yes, that's right. After gathering all the materials I built my first little railgun experiment.

Read the whole article after the break!

Let's first take a look at how a railgun 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 a railgun? 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.

(BREAK)

[Rodamala]

Plus, he has funny eyebrows.

[expat1000]

It’s not a big deal. Don’t worry about it.

[SunTzuWu]

Bookmark.

[reed13k]

For home fun later

[babygene]

"Tungsten is a very poor conductor though, hence its utility in light bulb filaments." Actually it is one of the better conductors. Material Resistivity Conductivity Silver 1.59×10−8 6.30×107 Copper 1.68×10−8 5.96×107 Annealed copper 1.72×10−8 5.80×107 Gold 2.44×10−8 4.10×107 Aluminum 2.82×10−8 3.5×107 Calcium 3.36×10−8 2.98×107 Tungsten 5.60×10−8 1.79×107 http://chemistry.about.com/od/moleculescompounds/a/Table-Of-Electrical-Resistivity-And-Conductivity.htm The reason it is used in filaments is not it's resistance but it's high melting point.

[Utilizer]

One of the comments left at the site states that one person tried using BBs but they kept welding themselves to the rails. Not sure if ball bearings would be much better. Stainless steel or chrome-plated ones, perhaps.

[Utilizer]

I now have a new favorite pasttime. Oh boy!

The hardest part might be the 400V power supply, but I think I have an old (about 1980) bug zapper that puts out either 360 or 400 volts. I'd have to find it and use the multimeter on it to be certain.

You might try mpja.com or this link:

How to make 400V PS

[Utilizer]

Don't forget it's 400 Volts which some standard wires are not designed to withstand too well. Add to that the energy surge from that bank of capacitors and you can do some accidental spot-welding if you are not careful.

You also might want to enclose the capacitor bank in a sturdy wooden box open on one side away from you just in case.

[Boogieman]

“Actually it is one of the better conductors.”

Well, it’s worse than most commonly used conductors, like copper, aluminum, or gold. You do have a point about the high melting point though, but the combination of relatively high resistivity and high melting point might not be good if you are subjecting it to a large magnetic field. A little too much induction, and while the tungsten won’t melt, it will emit black body radiation and might melt the railgun!

[Boogieman]

Here’s another 400v railgun project that explains a way to get around the welding problem, even if the projectiles are prone to it:

http://www.instructables.com/id/Rail-Gun-Linear-Accelerator/step4/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.”

So, just get the projectile moving a bit before it hits the rails and you should be okay. I bet a spring mechanism would work as well as compressed air.

[babygene]

“Well, it’s worse than most commonly used conductors, like copper, aluminum, or gold.”

Well, copper and gold melt at just under 2000 degrees F., and aluminum at 1200 degrees F. Tungsten is over 6000 degrees. I suppose you could use a copper projectile, but obviously not aluminum or gold. aluminum is too reactive with air as is calcium. Both would oxidize traveling through the air.

Tungsten is the best choice... And it’s relatively cheap.

[Boogieman]

“Well, copper and gold melt at just under 2000 degrees F., and aluminum at 1200 degrees F. Tungsten is over 6000 degrees. I suppose you could use a copper projectile, but obviously not aluminum or gold.”

Yes, but the conductivity and the melting point both come into play. The higher the resistivity, the more easily electricity is going to get converted into heat. So, tungsten can resist melting more easily, but it will also get hotter from the same amount of power. Those factors might end up negating each other for practical purposes here, but I wouldn’t know for sure unless someone tried it.

[reed13k]

And keep your wallet well away or the magnetic field could wipe all your cards too ;)

Worked MRs for a while - only takes forgetting once...

[TexasGator]

“Yes, but the conductivity and the melting point both come into play. The higher the resistivity, the more easily electricity is going to get converted into heat. So, tungsten can resist melting more easily, but it will also get hotter from the same amount of power. Those factors might end up negating each other for practical purposes here, but I wouldn’t know for sure unless someone tried it.”

I would comment on the above but I don’t have the time or the energy.

[Lurkina.n.Learnin]

BFL

[Boogieman]

Then why comment at all, if you aren’t contributing anything to the discussion?

[TexasGator]

” The higher the resistivity, the more easily electricity is going to get converted into heat. “

Increase R, I decreases.

Decrease I and P goes down exponentially.

Increasing R therefore decreases the amount of heat.

[babygene]

“Those factors might end up negating each other for practical purposes here, but I wouldn’t know for sure unless someone tried it.”

The closest actual experience I’ve had with such a device was 40 years ago when I made a gun that shot liquid mercury. It wasn’t exactly a rail gun since it used permanent magnets with the current passing through the mercury at a right angle to the magnetic lines of force. Of course in those days we didn’t have the super magnets that we have today.

[Hot Tabasco]

but this guy starts off with too long an anti-American

I think it was tongue in cheek and I thought it was a funny video.

[ForYourChildren]

Ya. That’s what I got out of it. I thought it was funny. And he did show how a railgun works.