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Coil Rifle w/ very high velocity

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Uriah

Sun Oct 07 2007, 07:08PM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

Hello all.

I am looking for guidence to begin designing a coil gun rifle with a projectile velocity of around 750m/s, while 600m/s would be acceptable. I have around $3,000 to pour into this project while I am awaiting the compleation of my other project, which has nothing to do with coilguns.

All I need are some general guidelines to start me off. I.e. Suggested voltage, kenetic J, stages, inductance or reluctance, etc...

Here are some inovations I plan on using to make the design more compact and efficienct.

Piezoelectric Transformers to provide the HV source.

Ceramic barrel (VERY STRONG MATERIAL) Only used in accelerator stage, after which continues with Al bore.

Power Components mounted on custom Bergquist ceramic circuit substrates w/ thermoelectric cooling panels instead of heatsinks.

All control circuitry will be SMD with a tight component layout. w/ microcontroller.

IXYS IGBTs for capacitor discharge.

I want to use a projectile no smaller then a .22 slug, most likely iron.

The last criteria is two round burst between recharging.

I just need a basic perspective on how this could be done, for starts on a benchtop setup.

Best regards,
Uriah George

Uriah

Sun Oct 07 2007, 07:24PM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

P.S. I am working with a gun specialist on this project so we can fabricate almost anything plausable under your responses.

Another note about velocity. I would like to reach 2500ft/s (750m/s) while anywhere from 1,500ft/s to 2,000ft/s would work. So 1,500ft/s (457.2 meters per second) is the minimum velocity acceptable.

I really do want to the projectile to have the diameter of a .22 cal slug (5.6-6mm approx).

Regards,
Uriah

Marko

Sun Oct 07 2007, 07:30PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Man, you should soften the criteria a bit for your projects.

First, what mass do you expect to launch 750m/s?
Tabletop coilguns have been made approaching the speed of sound,
but with quite light projectiles and not really high output energies.

Firing a 1g projectile at 750m/s requires 281.25 joules of energy.
Now if you have like 5% efficiency which is *good* you would need 5625J capacitor bank which will be size of a table even with electrolityc caps.

Realistic projectile mass for such a rifle would be like <0.1g as I think (28J.)

I don't know how could you launch such a tiny projectile at such speed - iron projectile would saturate too fast, and even for induction CG I fear your coupling would be too poor to transfer energy to the projectile.

I'm no expert on coilguns, but still that is an unrealistic proposal.
I've seen no CG rifle exceeding like few tens of m/s and this would be a giant leap.

Marko

Uriah

Sun Oct 07 2007, 07:37PM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

Well we are aiming for the impact strength of a .22 cal basic slug with a rifle size, what is suggested?

Bjørn

Sun Oct 07 2007, 08:03PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

What is the upper weight limit? You will need a backpack with 30kg worth of capacitors. In addition you need quite a lot of bits to make it safe.

I am not saying it is impossible, but it is not very realistic.

Marko

Sun Oct 07 2007, 08:10PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I think I can safely tell you to give that up.

Exceeding sound barrier with any projectile size would be enormous triumph for portable coilguns (considering you carry a large big cap bank on your back and etc.)

In order to match muzzle energy of 0.22 rimfire cartridge which is, according to wikipedia, 135J, you require something like 3kj cap bank which is size of a small desk and by no means portable.

If I was going to build a silent subsonic weapon my first choice would be air cannon.

Marko

Uriah

Sun Oct 07 2007, 08:25PM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

I'll take some humility on those notes! Thank you.

Best regards,

Uriah

Barry

Sun Oct 07 2007, 10:45PM

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

What you describe is really not a beginner project at all. Nor intermediate, for that matter.

If it's possible to build your coilgun at all, you'll need a multi-stage design. Each stage would impart a portion of the total kinetic energy ... as a random example you might have 14 stages, each of which is designed to add 10 joules KE. The (in)efficiency is such that you may well have 1KJ of stored energy in each stage.

Note that each stage is different; as the speed goes up, the firing time goes down. This typically results in lower inductance coils to achieve faster turn-off time. Also it means higher current peak in the waveform, as each 1KJ bank is discharged in successively shorter impulses. It's quite a very challenging piece of engineering, really.

You might consider relaxing one of the design constraints: try using a longer projectile. Shooting the same mass in a longer package allows you to use longer coils, and therefore the discharge times are longer. Discharging 1KJ in a longer pulse gives you a lower peak current in the switches. This makes everything easier (or maybe it just becomes possible) to build.

You mentioned a requirement for two shots in a row. For this you might consider a lower-voltage coilgun based on a large bank of industrial batteries. The available total energy is so much greater in batteries than capacitors, it's hardly comparable. The main challenge is then about how to minimize ESR and achieve the desired amp-turns in each stage, while controlling the turn-off time extremely well.

Here's another approach to consider ... If you have the skills for a 135J kinetic energy coilgun, then consider building a pulsed linear induction motor instead. The literature says energy conversion efficiencies can be in the range 10 - 20% or better. While our common garden-variety switched reluctance coilgun seems to be limited to 1 - 2% at high energies, and only reaches 5% at low energy. Everyone on this forum would love to have some trailblazer create a decent PLIM that we can learn from!

Cheers, Barry
There are two rules for success in life ... Rule 1: Don't tell people everything you know

...

Mon Oct 08 2007, 01:53AM

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

As noted earlier, you probably aren't going to get >5% efficiency, so to get 150J out you need 3Kj of caps, which all considered isn't that horribly large. It could be made to fit into a backpack.

But I think that you are going to end up dying on the switches, wiring, etc. Think about it, if you are shooting a .22 sized bullet (say 5mm long) and shooting for 750m/s, your pulse length will be 6uS.

I am not even sure that is possible using electrolytic, and definitely not possible using IGBTs

Electroholic

Mon Oct 08 2007, 02:08AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

This is the fastest induction launcher i've seen, and still not even close to what you are shooting for.

Click on induction gun 2

total energy 1kJ, 10%efficient.
muzzle velocity is just under the speed of sound.

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