Home Made Rail Gun

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eggs
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Home Made Rail Gun

Postby eggs » Thu Nov 11, 2010 12:53 am UTC

I used the search bar and i don't think there is another post for this...
I'm think about building a rail gun but I'm not exactly a genius engineer or physicist (sophomore in high school) and i would appreciate it if anyone would give any tips like the optimal size of the rail and the right capacitor setup etc.

EDIT: What kind of charger would you recommend? and also if you do recommend one please tell me the max voltage for it.
Last edited by eggs on Sun Nov 21, 2010 4:26 am UTC, edited 1 time in total.

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LucasBrown
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Re: Home Made Rail Gun

Postby LucasBrown » Thu Nov 11, 2010 12:57 am UTC

You don't want to mess with rail guns unless you really know what you're doing... That being said, you can find instructions fairly easily with Google.

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eggs
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Re: Home Made Rail Gun

Postby eggs » Thu Nov 11, 2010 1:11 am UTC

Well...i know not to electrocute myself with the capacitors cuz i realize that there's quite a lot of voltage in there and yes i have found a few good instructions on Google but i thought i would make a post here since there's a lot of smart and helpful people. I already have plans so if no one posts anything here I'll be still fine but tips would be quite helpful.

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LucasBrown
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Re: Home Made Rail Gun

Postby LucasBrown » Thu Nov 11, 2010 2:35 am UTC

It's not just the capacitors that are dangerous. I tried to make one myself and had no problem with the electronics--the problem came from the structural integrity of the materials. The "barrel" quite literally blew up in my face.

Korrente
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Re: Home Made Rail Gun

Postby Korrente » Thu Nov 11, 2010 4:02 am UTC

Just curious, but what kind of caps did you use, Lucas? I wanted to build a small one myself a while back but everything I found was too expensive.

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Solt
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Re: Home Made Rail Gun

Postby Solt » Thu Nov 11, 2010 10:54 am UTC

ALWAYS wear safety glasses. Regular glasses don't count. They have to be shatter resistant.


With that said, I think the biggest problem is getting the capacitors. They're quite expensive new and legit. Unless you have unlimited funds, the rail gun won't happen until after you somehow acquire a good number. I suggest junkyards.
"Welding was faster, cheaper and, in theory,
produced a more reliable product. But sailors do
not float on theory, and the welded tankers had a
most annoying habit of splitting in two."
-J.W. Morris

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eggs
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Re: Home Made Rail Gun

Postby eggs » Thu Nov 11, 2010 2:41 pm UTC

The funny thing is my mom is on a busyness trip in china right now and she'll be able to get the capacitor im looking for for a lot less money. (LOL). If your curious im getting about 24 capacitors, each of them have 330 volts and 120 micro farads.

Carnildo
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Re: Home Made Rail Gun

Postby Carnildo » Fri Nov 12, 2010 7:27 am UTC

On the subject of homemade railguns, how well do they scale down? Is it practical to make a railgun sized for chucking bits of copper wire into a dartboard across the room?

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Solt
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Re: Home Made Rail Gun

Postby Solt » Fri Nov 12, 2010 9:03 am UTC

eggs wrote:If your curious im getting about 24 capacitors, each of them have 330 volts and 120 micro farads.


You realize that's only about 150 Joules total, right?

You're going to have to do better than that dude. What are you paying here and there?
"Welding was faster, cheaper and, in theory,

produced a more reliable product. But sailors do

not float on theory, and the welded tankers had a

most annoying habit of splitting in two."

-J.W. Morris

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eggs
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Re: Home Made Rail Gun

Postby eggs » Fri Nov 12, 2010 12:50 pm UTC

You realize that's only about 150 Joules total, right?

You're going to have to do better than that dude. What are you paying here and there?


Yeah, i this just a prototype kind of deal, once i get this right I'm going to scale it bigger. I'm expecting something like 10 m/s from a aluminum foil ball, probably even less

Aussie_Sniper
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Re: Home Made Rail Gun

Postby Aussie_Sniper » Sat Nov 13, 2010 10:37 am UTC

eggs wrote:
You realize that's only about 150 Joules total, right?

You're going to have to do better than that dude. What are you paying here and there?


Yeah, i this just a prototype kind of deal, once i get this right I'm going to scale it bigger. I'm expecting something like 10 m/s from a aluminum foil ball, probably even less


An aluminium foil ball is a poor choice of ammunition. Try to find something more rigid and conductive. Do you have access to any sheet metal (preferably copper)?

Winter Man
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Re: Home Made Rail Gun

Postby Winter Man » Sat Nov 13, 2010 4:04 pm UTC

Tungsten welding rod makes a great projectile.
Explosion, WAH!

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rath358
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Re: Home Made Rail Gun

Postby rath358 » Sat Nov 13, 2010 8:46 pm UTC

eggs wrote:The funny thing is my mom is on a busyness trip in china right now and she'll be able to get the capacitor im looking for for a lot less money. (LOL). If your curious im getting about 24 capacitors, each of them have 330 volts and 120 micro farads.

"Average" caps from the flash mechanism of a disposable camera should be of similar power*. If you ask nicely, your 1-hour photo center should be able to give you a bunch of old disposable cameras**.

*reference:
http://en.wikipedia.org/wiki/Photoflash_capacitor


**Ours would. YMMV

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eggs
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Re: Home Made Rail Gun

Postby eggs » Sun Nov 14, 2010 5:55 pm UTC

rath358 wrote:"Average" caps from the flash mechanism of a disposable camera should be of similar power*. If you ask nicely, your 1-hour photo center should be able to give you a bunch of old disposable cameras**.


that wouldn't be needed, my mom just came back from china and the caps were a lot cheaper than i though: 3 yuan per cap and they are 400volts 150 farads, so she bought 36 of them.

Edit: yes it's 150 micro farads. It was a typo.
Last edited by eggs on Tue Nov 16, 2010 1:34 am UTC, edited 1 time in total.

Meem1029
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Re: Home Made Rail Gun

Postby Meem1029 » Sun Nov 14, 2010 6:31 pm UTC

150 microfarads perhaps? 150 farads would be absurdly large. If I remember correctly the average 1 farad capacitor is quite large, larger than a can of pop for sure. I can't imagine what a 150 farad capacitor would look like.
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Soralin
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Re: Home Made Rail Gun

Postby Soralin » Sun Nov 14, 2010 11:16 pm UTC

Meem1029 wrote:150 microfarads perhaps? 150 farads would be absurdly large. If I remember correctly the average 1 farad capacitor is quite large, larger than a can of pop for sure. I can't imagine what a 150 farad capacitor would look like.

Maybe for ones that aren't supercapacitors, but since those have been developed, they've had a massive impact on what you can do in a certain size. (Although at 400v, that's not likely going to be a supercapacitor)

http://en.wikipedia.org/wiki/Electric_d ... _capacitor:
An electric double-layer capacitor, also known as supercapacitor, supercondenser, pseudocapacitor, electrochemical double layer capacitor (EDLC), or ultracapacitor, is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors, typically on the order of thousands of times greater than a high capacity electrolytic capacitor. For instance, a typical D-cell sized electrolytic capacitor will have a capacitance in the range of tens of millifarads. The same size electric double-layer capacitor would have a capacitance of several farads, an improvement of about two or three orders of magnitude in capacitance, but usually at a lower working voltage. Larger double-layer capacitors have capacities up to 5,000 farads as of 2010[update].[1] The highest energy density in production is 30 Wh/kg,[2] below rapid-charging Lithium-titanate batteries.


See for example, pulled off of a google page:
http://www.rell.com/Pages/Product-Detai ... tId=924890
Image
From the specs sheet, the 150F capacitor there is 50mm(just under 2 inches) long (not including the contacts), with a diameter of 25mm.

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Solt
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Re: Home Made Rail Gun

Postby Solt » Mon Nov 15, 2010 2:17 am UTC

Yea no point in going into the Farad range because you lose voltage, and as we know from the energy equation, .5*C*V^2, high voltage is more important than high capacitance. But that's only after a point. For example OP could obviously increase Capacitance by a few orders of magnitude without sacrificing voltage. I believe there are current limitations to consider as well.

eggs wrote:that wouldn't be needed, my mom just came back from china and the caps were a lot cheaper than i though: 3 yuan per cap and they are 400volts 150 farads, so she bought 36 of them.


What does your power supply and voltage boost setup look like? I had a tough time building a voltage boosting circuit without ordering special parts, but back then I knew a lot less about electronics.
"Welding was faster, cheaper and, in theory,

produced a more reliable product. But sailors do

not float on theory, and the welded tankers had a

most annoying habit of splitting in two."

-J.W. Morris

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eggs
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Re: Home Made Rail Gun

Postby eggs » Sun Nov 21, 2010 9:09 pm UTC

I really have no idea how the setup for the cap should be...right now im going to be using a single charger from a disposable camera and it has 300 volts tops so im just going to connect all 36 of my caps in parallel.


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