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4mm ETG

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4mm ETG

Unread postAuthor: 245Tommy » Sat Jan 16, 2010 3:18 am

I built this out of parts I had lying around, the barrel is three brass tubes epoxied together, the electrode is a screw with an epoxy insulator. 370joule 660v capacitor bank. Switch is a 40amp auto relay with homemade contacts. The ammo is a wooden dowel wrapped in tape with a chunk of lead or a nail glued on the tip.
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 16, 2010 3:24 am

Kudos for making it work, what's the performance like?
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Unread postAuthor: 245Tommy » Sat Jan 16, 2010 1:07 pm

The first shot was a soda can full of water at 270joules with the lead slug, the next shot was a lead slug with one slit cut in it like a dum-dum bullet into clay at 370joules. I lined up four pennies and the dart went into two of them and then curled back into the second penny and skewered them together.
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 16, 2010 1:40 pm

Impressive! Any plans to make it portable or will it remain a benchtop project?
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Unread postAuthor: 245Tommy » Sat Jan 16, 2010 2:44 pm

jackssmirkingrevenge wrote:Impressive! Any plans to make it portable or will it remain a benchtop project?
Maybe if I could make it practical, I have an idea for a preloaded cartridge.
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 16, 2010 2:48 pm

245Tommy wrote:I have an idea for a preloaded cartridge.


A man after my own heart :) well if Larda's monster is anything to go by, you could conceivably make one powerful enough to work a recoil powered action.
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Unread postAuthor: jrrdw » Sat Jan 16, 2010 5:14 pm

Does this count for DYI's coin challange? Lets find out shall we...Nice work 245Tommy :D .
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Unread postAuthor: rp181 » Sat Jan 16, 2010 7:13 pm

Every ETG I see makes me think more and more I should make a 12kJ one that actually uses high efficiency techniques. I think with some work, I could match larda's power.

Nice job!
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Unread postAuthor: kjjohn » Sat Jan 16, 2010 7:52 pm

Looks great. It would be awesome if you could make it into some form of rifle or pistol design.

Ever think of using ultracapacitors? They can store up to hundreds of times the energy of electrolytic caps (1000+ farads) in an extremely small package. They also have extremely high amperage, and their voltage can be boosted by discharging into an ignition coil
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Unread postAuthor: 245Tommy » Sat Jan 16, 2010 9:07 pm

kjjohn wrote:Looks great. It would be awesome if you could make it into some form of rifle or pistol design.

Ever think of using ultracapacitors? They can store up to hundreds of times the energy of electrolytic caps (1000+ farads) in an extremely small package. They also have extremely high amperage, and their voltage can be boosted by discharging into an ignition coil
I don't think they work for very fast discharges.
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Unread postAuthor: kjjohn » Sat Jan 16, 2010 9:09 pm

Normally ultracaps discharge within a few seconds, but if you wired many of them in series, it would lower the capacitance, which I believe would make the discharge quicker. I'm not quite sure, but boosting the voltage with a coil may do the same. I guess you would know for sure, you've built one that seems to work pretty well. In terms of HV, I have only worked with smaller electrolytics in a coilgun.
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Unread postAuthor: rp181 » Sat Jan 16, 2010 9:10 pm

kjjohn: completely wrong. Super capacitors would be destroyed very quickly, they do not stand high currents at all. Farads is not the only measure of energy, voltage matters too. Supercapacitors have low voltage ratings.
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Unread postAuthor: kjjohn » Sat Jan 16, 2010 9:16 pm

I don't have any experience with ultracaps, and not much experience with any other kinds of caps, so I don't really know that much about them. :) However, like I mentioned before, you would boost the voltage by discharging the cap through a coil or wiring many in series. What do you mean by "Super capacitors would be destroyed very quickly" though? Are you talking about the induced back voltage/current that appears after the coil discharges?
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Unread postAuthor: chinnerz » Sat Jan 16, 2010 9:41 pm

dont ultracaps take up to 20 seconds to discharge? i know mine dose, i was seing if it could be used as a quick charge battery... for an IR flash
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Unread postAuthor: chinnerz » Sat Jan 16, 2010 9:42 pm

.0(&*
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