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Blowback spring

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Blowback spring

Unread postAuthor: daccel » Tue Jan 13, 2009 12:58 am

What would be the best spring for a direct blow back hybrid cartridge? A regular steel spring or an air spring?

I could make the steel spring adjustable by having a bolt behind it that would change the pre-compression as it moved in or out, and the air obviously would be adjustable by pressure. The air would require orings though, so more work.

Not sure about the spring rate and how the two would compare as they compressed back. With air I suppose you could have a reservoir and keep the spring force almost constant throughout cartridge travel. I think that would let you maximize the time the cartridge was sealed to the barrel, because you could use a higher initial spring force. The steel would get much stiffer as it moved back, so you would have to use a lower initial force or it wouldn't eject.
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Unread postAuthor: Lentamentalisk » Tue Jan 13, 2009 10:26 am

If you just extended the spring beyond where you want the cart to stop, then it would have the same effect. The only problem there is that you are limited to springs needing a pretty straight pull (or push) while air can be bent up as much as you want.
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Unread postAuthor: ramses » Tue Jan 13, 2009 3:40 pm

air would be more practical, especially if you were going to use a large diameter cartridge.
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Unread postAuthor: daccel » Wed Jan 14, 2009 2:16 am

Yeah the air would allow more flexibility for layout. More important when moving beyond a proof of concept, but might as well start designing that in early.

Well, you could always use car springs.. :shock:. But no, I'm thinking more along the lines of what qualifies as micro in the hybrid world.

Air 2 spring 0, time to go oring shopping.
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