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Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039
The thing I'm seeing come up the most between you two, is the reason of building such a thing. Most of the reason is for concept. I think it would be fun to have a ETG as a "Did you know you can vaporize foil into plasma fast enough to shoot a projectile ...". I'm building it more for a concept and experiment, than I am for using it a lot. I never got much into the ETG field yet, so I wanted to experiment to see what works good. Will add more to this another day answering other questions, but I'm on my iPod as for now :P
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039
If I had a mill I would put more effort into it as I would be able to make an air tight seal, as well as a good ignition source. But since I don't, I'm stuck with pipe and pipe fittings.
Registered Member #1917
Joined: Fri Jan 09 2009, 02:38AM
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Posts: 62
Ah, I must have missed the part where you said you wanted a harmless toy. The solution is still similar to a capillary tube plasma generator, and it can be done with low voltage electrolytics. I ran one of these as low as 1.6kJ with what I guess were passably good results.
Have the current path go from one end of a small plastic tube to the other via an aluminum strip, and add a small quantity of water if desired (the interior should just be wet, not full of water). The plastic tube should be coaxial with the barrel and replaceable, as it'll be carbonized and partially ablated with every shot. You can use epoxy cast inside pipe fittings to get the interior shape you need, and all-thread steel rod for the rear electrode. Your electrothermal pressure generation will take place inside the tube and the gas will be expelled into the barrel, pushing the projectile.
So long as you stick to very low voltage, probably 1.5kV or so, this configuration will only generate a few thousand psi and should be easily contained by a combination of brass pipe fittings and high quality epoxy. It won't be spectacular, but it's built with the same principles that make a good design, so you can be comfortable in the knowledge that you're doing the best you can with what you have. Running at 1kJ input, it'll be a nice little indoor plinker with similar muzzle energy to a good slingshot, if built well.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
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Well so far at 350v out of 450, this was on the PCB system, it shot a capacitor through the bottom of a soda can, aka the hardest spot. i thought that was rather powerful, until the plastic failed. the current metal one works fine, im just too busy with a DRSSTC and college stuff right now...When i get time ill test it at the series parallel config of 900v 1KJ
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Rifle based ETG
