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New Gauss Rifle

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Remus

Thu Mar 23 2006, 08:54PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

Ok, I totally realize that a million and one people have already posted things like this b4. And I know Yohan gets mad when noobies ask about how to make a coil gun and all that. Im designing a coil gun in my free time. One that has like 4 stages. will have a semi-automatic loading area for the projectile, preferebly, if i can, carbon fiber body to the rifle. but back the the coil gun itself...how do I determine how many turns to have in my coils? And a slightly stupid question, I keep hearing about the 555 timer, what is it used for in a coil gun?

Although Im sort of a newbie in this stuff, I have been researching a lot of this in my free time, and Ive just now gotten around to start designing things.( also b/c im taking a electricity and magnetism class in college) Hope anyone can help, thanks.

...

Fri Mar 24 2006, 12:14AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Determining how many turns is a tricky thing to do...

There are 3 basic parameters in a coil gun: voltage, current, and pulse length
The voltage will be determined by your cap bank (however high you charge it is your voltage)
The current/pulse length are inversely related to each other (ie higher current = shorter pulse), and the pulse length is directly related to the capacitance of the cap bank. The inductance/resistance of the coil is directly related to the pulse length.
So to tune the coil gun you need to change either voltage, current, capacitance, or change the inductance/resistance of the coil.
So once you have decided on the voltage/capacitance you are going to use, you need to decided how much inductance/resistance in the coil you need. You want the resistance as low as possible, but using bigger wire makes the coils larger/less efficient; so you need to find a tradeoff between the two that is most efficient. Most people just use whatever they can find in the 20awg-10awg depending on the energy stored in the bank.
But more importantly you need to decide on how much inductance (turns) you need. You want to keep it as high as you can (to reduce the current so you can use a cheaper switch), but if it is too long the pulse length will be too long and you will get 'suckback' where the coil is on after the projectile leaves so it gets sucked back in.
It is hard to calculate all of this, so most people just use a simulator and twiddle with the values until you get the highest efficiency. Unfortunately I have yet to find a simulator that takes into account the maximum pulse length before you get too much suckback, so you just have to figure it out on your own. If you use this simulator it gives you the pulse length. If you plug them in to this one it will give you a velocity. And you know the length of the coil. Because you want to pulse to have ended by the time the projectile is through the coil, you can take the length of the coil (in feet)*the velocity (f/s) and get the time. As long as this number is less that the pulse length you should be ok.

As to the 555, it is used for a plethora of uses.
I am guessing what you are asking about is a pulse generator used in IGBT based guns. Instead of using an switch that is on all of the time (like a scr) and tuning the coil to fit their bank, they use an oversized cap bank (more capacitance than is in tune with the coil) and use the switch to turn off the pulse when the projectile leaves the coil. This gives more efficiency, and makes the design more complex.

They are also used pretty extensively in the power supply to charge the cap bank. Both in boost converters and to drive a (or several) switch, and then the resulting signal is fed into a transformer to get the necessary voltage.

I hope at least some of that made sense...

Good luck!

Simon

Fri Mar 24 2006, 01:14AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

So you want to make a coilgun? A gauss gun is something different. At least what I know of as a gauss gun.

I wouldn't recommnend a four stage if you aren't quite sure about the number of turns. Remember, a good four stage CG is made up from four good single stage CGs so experiment with single stage first.

Remus

Fri Mar 24 2006, 06:22PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

Thanks Guys, that should help me getting up to speed. Hopefully, I'll be able to get a design going soon. 1 stage sounds good. 2 questions tho. does anyone know where I can get a projectile made? the steel bullets...and second, Simon, what exactly is a gauss rifle, if its a different thing from a coil gun? I thought they were the same thing, just referred differently.
Thanks.

The Zander

Sat Mar 25 2006, 06:45AM

Registered Member #295 Joined: Tue Mar 07 2006, 06:59PM
Location:
Posts: 23

I've been building coilguns for quite sometime now, and i've found that the easiest (perhapes not THE best, but definately the easiest) way to calculate parameters for a coilgun are as follows

1. Decide on a projectile, i'd recommend finding somthing in the ~10-20g range for low power coilguns, but really it's totally upto you, just remmber that heavier projectiles may be slighty more efficent but will not travel as fast (if your looking for the holy $HIT factor, you need a light/fast projectile

2. Once you know the mass/length of your projectile you can determine an approximate final velocity using the forumla MV1^2=(0.03)CV2^2 where M is the mass of the projectile, V1 is the muzzle velocity of the projectile, C is the total capacitance of the capacitor bank, and V2 is the total bank voltage. this formula is a combination of the formulas for kinetic energy of a mass, and the formula for the potential energy stored in a capacitor. it assumes a 3% efficiency. and obviously you are going to need to isolate V1 in the above equation to find the velocity (i just have no idea how to write sqrt() signs using the forum interface)

3. Now you know the approximate final velocity of your projectile (emphasis on approximate) you can calculate hwo long your pulse length should be to maximize energy transfer. in order for this to happen there should be a magnetic field present around the coil (aka: current is flowing through the coilg) for the entire time the projectile is within the coil, AND NO LONGER. if the pulse length extends beyond this the magnetic force will remove kinetic energy from the projectile as it tries to pull it backwards. use the formula V=D/T. your projectile and coil should be the same length (imperical evidence suggest this is very efficient) therefore you are really just trying to find how long it takes your projectile to travel the length of the coil. say your coil is 3cm long, and your muzzle velocity is 10m/s (you can do better than this, it's just a nice number to work with). therefore your target pulse length should be T=D/V, T=(0.03m)/(10m/s), T=3mS (milliseconds).

4. now you can check you the coilgun simulator on barrys coilgun site (great resource for beginners like yourself) and design a coil with that pulse time in mind.

Just my $0.02
-The Zander

ps. i appologize in advance for any spelling/grammer errors inthe above text, it's late, enough said.

Barry

Mon Mar 27 2006, 01:28AM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Zander, awesome post, nice description -- it's exactly the approach that I would recommend to anyone starting a new coilgun. So I'm just adding a "me too!"

Cheers, Barry
Also, here is a link to the coilgun simulator that will help you determine part values for a desired timing

Quantum Singularity

Mon Mar 27 2006, 05:17AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I have not yet come across any reputable site indicating the a Gauss Riffle is something specificaly different than a coil gun. The common defenition with a quick google search indicates a Gauss Riffle is a magnetic linear accelerator. That can include a whole host of different types of magnetic guns. Also, according to Wikipidia http://en.wikipedia.org/wiki/Coilgun

A coilgun (also known as Gauss gun, Gauss cannon or Gauss rifle) is a type of cannon that uses a series of electromagnets to accelerate a magnetic shell to very high velocities. The appellation "Gauss gun" comes from Carl Friedrich Gauss, who formulated mathematical descriptions of the electromagnetic effect used by coilguns.

The best site I have found so far that clearly explains the different types of coil guns is Coilgun Systems, try this http://www.coilgun.eclipse.co.uk/coilgun_basics_3.html
(use the arrows to view all 3 pages).

I beleive the term coil gun here on 4hv usually refers to the reluctance type coilgun. I have not built one of these myself yet, I have built a few different variations of inductance/reconnection type coilguns though. Good luck!

Remus

Tue Mar 28 2006, 09:04PM

Registered Member #342 Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20

Thats some great Info guys. Thanks a lot. I'll keep y'all posted on anything new I come across while building this.

Where would I get the projectile made though? I wanted to make it hollow point, with a helical cut into the projectile...maybe fill it with some epoxy. Any ideas where to do this or with what equiptment, if I were to do this myself?

FastMHz

Tue Mar 28 2006, 09:56PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

I think generally you'd want your slug to be solid metal, not hollow or filled with nonmagnetic material. I make mine by chopping the head off a bolt, sticking it into my drill and using my bench grinder to make a point.

Self Defenestrate

Tue Mar 28 2006, 11:14PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I'm a fan of the drill and dremel aproach. Find a steel/iron rod of correct diameter and cut it to the projectiles length. Chuck it up and grind it with a dremel attachment for the desired point. This setup makes polishing real quick too.

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