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Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
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My first coilgun, was a wth i'll just put stuff together. shot 5mm. wow! fail.
So, after a few years of going around..i found 400V 470uf capacitors (4 of them) can shoot a bolt though a can. Now a guy on instructables, charged his to 800V using only 4 of those capacitors (2 in series) and shot though a coffee can and hit his wall behind it.
My question:
Yet mass of object matters, if i was to use 4 of these 400V 470uf capacitors, How big of a barrel do i need to be able to puncture a coffee can? I mean loading a object in a Straw from a restaurant, wont do me any good will it?
Registered Member #1633
Joined: Tue Aug 12 2008, 04:21AM
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Well, you'd be suprised how much power you can direct through a coil formed on a straw. as long as it is one of those drinking straws and not those coffe stirrers, you should be fine. I'd use 24 awg magnet wire from radioshack, say about 5 layers, 1" long. While it is true that increasing speed does more for a projectile than increasing mass, heavy projectiles transfer their energy more effectively to the target.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
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youngcoilgunner wrote ...
Well, you'd be suprised how much power you can direct through a coil formed on a straw. as long as it is one of those drinking straws and not those coffe stirrers, you should be fine. I'd use 24 awg magnet wire from radioshack, say about 5 layers, 1" long. While it is true that increasing speed does more for a projectile than increasing mass, heavy projectiles transfer their energy more effectively to the target.
Yup, Was going to try a drinking straw. I'll try your amount first then i'll try the others guys amount, i think 20 mm wide and 12 layers. Would u recommend 4 or 10 of those 400V 470 UF?
Registered Member #1262
Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451
If your goal is to shoor through a can, I'd say go with more capacitors. One thing for sure is, try a semi-wadcutter tip on your ammo, you'll have much better odds that way.
I calculated your caps are 37.6J each, getting through a coffee can shouldnt be too hard with either four or ten.
BTW Don't forget the protection diodes! Theres nothing worse than losing your caps in the prime of their life!
Registered Member #1643
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Backyard Skunkworks wrote ...
If your goal is to shoor through a can, I'd say go with more capacitors. One thing for sure is, try a semi-wadcutter tip on your ammo, you'll have much better odds that way.
I calculated your caps are 37.6J each, getting through a coffee can shouldnt be too hard with either four or ten.
BTW Don't forget the protection diodes! Theres nothing worse than losing your caps in the prime of their life!
I heard they can actually take some power away. what's the best rated diodes to get? maybe ill try 6 first, and see how it goes, save some caps maybe hah ;P
Registered Member #1633
Joined: Tue Aug 12 2008, 04:21AM
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Nope, they do not take any power away, only the unwanted power that can destroy your capacitors!! If your going for any cap value larger than 1000µf @ 260v or higher, use larger magnet wire, and alter your layers a bit. I had a model (which was recently scrapped) that only used 560µf capacitors rated at 450V, though I only charged them to 260 (it took too long). I used the 24 awg and the coil diameters set above, and was able to launch a 4.5 gram projectile 50 feet!, Not quite the power your looking for, but if you use 2 stages (W/ same parameters as the first stage), scr triggered and phototransistor sensing, you can easily pierce a can (I did that with a 4" long, 1/4" wide tempered steel nail). it actually continued through the other side, but got stuck. I'd say about 5 stages is really the most you'll want to do, any more will have little or no benefit.
Registered Member #1643
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Hmm yeah, I was just going for straw barrel and get a round to fire though the first side at LEAST but, i can try like the other guy said and use like 4-6 with a 1 inch 5-12 layer coil. I found a guy that got his to fire using the same capacitors, like i said 20mm and 12 layers.
Also, it is Washer:Coil:Washer right? no cardboard between the coils and the steel washer?
Registered Member #1633
Joined: Tue Aug 12 2008, 04:21AM
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I wouldn't use a washer; you read this on barry's coilgun site that washers, despite directing flux lines toward the projectile, external Iron is subject to heavy hysteresis losses. What you could try is cutting the washer in fourths, covering them in enamel, and then assembling the quartered washers nearest to the projectile's end of the coil just as if it was another washer. The coil and washer will act like a transformer, inducing current flow in the washer which reduces from the overall current available in the magnetic field, but quartering it in this way should reduce those losses significantly.
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