Coil Gun

[yorgie]

so if the guywith the $0 coil gun charges it with a camera flash curcuit, i'm going to need to hugely oversize that to form any way of charging 2 24 capacitor beds (it needs to be 24 in each to run 4 in parallel as the guy with the railgun did). i think this means itll take a few days to charge, unless i get my thinking cap on! 2 beds of 24 4.7F capacitors is going to generate - 225.6F, arround as much as the railgun dude. I think this is going to kill someone, i'm worried!
Do you think he used Lexan to make that box for his capacitors, or just clear pvc?
the fittings are large, thin copper sheet metal, which is easy to get hold of. When i get back from my holiday, i can begin construction

plus i know this is going to be me playing with silly voltages, so i'm going to need to suit up - layers of rubber gloves I am still not sure how i can turn the stored current from DC to AC from the capacitors to the coiled wire, in a short period of time - any ideas?

 

[Strawb]

If it's a coil gun your looking at then you don't need AC, a DC coil will attract a iron slug perfectly well.
You won't need banks and banks of capacitors, scale down your cannon and start out with a small ball bearing as a projectile.
2 or 3 12v car batteries in series with some fairly low resistance coils should be plenty.
It's still the switching circuit that is going to be the hardest part to build/time.

 

[Skeet]

How does teh Coil gun guy do it...one of teh links I posted..if you look...has a 30cm tube, fitted with coils all teh way along, 16 stage I believe,,,he uses otical sensors to detect the pressence of teh projectile, and hence switch teh next coil...they look like HALO eyes! so you could use those.
Then you will need something that can detect teh eyes output, and swicth on teh next coil.

If you want projectiles..i can supply you with .308 Bullets (just teh bullet) copper jacketed around 168 grains in weight, not sure i fthey will be useable in a rail gun, but should be fine in a coil gun.
The guy in one link, found that he had a 2% increase in performance by using a plastic tube rather than metal.

http://www.coilgun.eclipse.co.uk/16_stage_opto_prototype.html

 

[yorgie]

mmm they look like delrin sleeves for the optical sensor, i don't know if halo eyes will be able to keep up with the speed of the exiting projectile, but it's possible.

In referance to using live ordannace as a projectile, is there any risk of the casing contacting with the coil and firing off? i think the slug would be great, off the front, but i know how expensive live ordanance is, so i'd feel guilty taking that off of you! Also, as this would be VERY conisistant, surely a timing circuit would work as well as an optically sensored circuit, but i'll look into both. Do you think i could buy halo eyes in bulk somewhere . I will only need 12 caps i think with this coil gun, as it won't need too much in terms of stored energy, especially if i use like.. a 16 stage

 

[Strawb]

Don't think copper projectiles will work, they need to be ferrous so their attracted to the coils.
It can be done with eyes (and will probably produce the best results), though would be simpler to just have a timing system to turn the coils on and off in sequence.

Look into something like a basic stamp for timing, you'd need to keep the code simple but it should be fast enough to fire 15 to 20 coils. Relays would be easiest but for something like this the switching times (or difference between switching times of several relays) may cause issues so you may have to use power darlingtons, good news is they can be switched directly from a basic stamp.

 

[Skeet]

http://www.coilgun.eclipse.co.uk/electromagnetic_pistol_final_assembly.html

OMG!
Check this site out...he knows his ****!

Erm...to correct you..I have "Live Ordanance" however, i would never give, lend sell or otherwise put into a persons posession, such items...as it would be highly illegal for both of us.

What I was reffering to...was teh Bullet itself (just teh pointy bit!).
But being copper and I think lead core, wouldnt work.

What you need, from reading the info...is a powdered matrix projectile...basicly..powdered ferrous material, Iron et, which is held together with epoxy...so you could mould them basicly...or...turn them.

The trouble with timing it, is the fact that it will be accelerating..and unless you know teh exact point that it reaches teh CENTRE of teh coil, then its no good.

You have to switch off teh first coil at teh moment teh projectile reaches teh centre of teh coil, for it to have again in accelleration, and then switch on teh next coil in the series...by using eyes (which lets face it, operate at teh speed of light), you could position them such that they detect teh nose of teh projectile.

In the link above, the guy makes the coils 25mm in length and teh projectiles as well, that way he knows whats what.

 

[yorgie]

i'm off for the night but i'll have a think about it - A simple tube design, such as aluminium appears best, as although compared to plastic as skeet has said it'll take a 2% hit, i'll find it easier to machine slots into aluminium than pvc, without shattering it. Delrin is easy to machine, so that won't be an issue, as i can just machine a core of it, and cut it into slices for each stage.
Coil cable will be cheap.
Capacitors are cheap (6800mF caps for £6).
Car batteries, if i can get them second hand are fairly cheap.
If i can find a good machine shop locally i can get a board pressed for firing off 18 odd stages.
I can machine a case for the whole thing, i'll keep it's size to a minimal ammount, i want to be able to transport it, and as it's entirely recoil less, fire it by hand.
The coil design will heat up, but that will only be comparable to the time it takes to charge about 8 - 12 capacitors, so it wont melt the copper, i hope - if not, i'll look into vapour cooling.
Anyhow, i'll sleep on it
How much are halo eyes?

From skeet's above post - i am proficient with a lathe, i can easily turn a projectile, although steel bolts seem to be a cheap alternative

 

[Skeet]

Have you even looked at teh links I posted?

halo eyes are cheap enough mate

The guy has built a working pistol..for gods sake man look!!!!

We allready know, taht a plastic core is better...and you wont need to cut slots in it, slots are for metal cores!

 

[Strawb]

Parallax who do the basic stamp.
http://www.parallax.com

And the UK distributor
www.milinst.com

For eyes if you want to go that way(i don't think it's required, at least not for a prototype) can be bought from Maplin.
www.maplin.co.uk
Can't remember exactly the cost of eyes but less tha £2 a pair.

Where do you get the idea that it's recoil-less? If you accelerate a projectile the gun will kick.

Capacitors being charged off a car battery will be charged in ms (though resistors will increase the chgarging time and help prevent damage to them from charging too quick), unless your using some kind of inverter to charge the to higher than battery voltage?

 

[yorgie]

skeet i did look at that link, it is an awesome little pistol!

And as for pvc tubing, i will just use that then.

Strawb, those optical sensors seem to be just the ticket, and that stamp could be what i'm looking for - as a prototype, i just want it to fire off, size and appearance won't matter, i can make it fancier later, and tweak it, maybe run an lcd screen off of it, but that'll come later on!
And for safety, i'll run a breaker on it, i just need to find a large capacity breaker.
thanks for your help, i'll thnk about the design overnight.