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Hybrid Wiring Outside to Inside of Chamber

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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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: WizardNoodle » Tue Mar 28, 2017 1:14 pm

auxiliary wrote:Oh yeah, I think you are on the right track there. Try checking out you locals dealers, you never know if you have something good in your backyard. I would throw a safety factor on top of those working pressures though because of the repeated shock loads. To do that, you gotta learn a bit more about fatigue: https://en.wikipedia.org/wiki/Fatigue_(material)


Read the page and redirected to Fatigue Limit. "Typical values of the limit (Se) for steels are 1/2 the ultimate tensile strength, to a maximum of 290 MPa (42 ksi)." So the general fatigue limit of steel is 42000 psi?
Correct me if I'm wrong, but in this case I'm not sure the fatigue limit matters as much with steel. Of course not being sure means that Murphy's law probably applies and I will end up blowing myself up because of a stupid mistake, any thoughts on preventing this inevitable cause of self-ignorance?
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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: D_Hall » Thu Mar 30, 2017 12:28 am

auxiliary wrote: If you wish to calculate the theoretical burst pressure of any kind of pipe you can use Barlow's formula: http://www.engineersedge.com/calculators/pipe_bust_calc.htm

It's worth noting that Barlow's formula is a thin-walled approximation that yields results that are in excess of actual capabilities. The thicker the wall of the pipe, the crappier the results from Barlow. So.... If you're using thick walled pipe, DO NOT think you're safe just because Barlow says it won't burst. Use the thick walled equations. A bit messier, but more accurate.

Other thoughts....

Sign me up as a "use a spark plug, this is what they're designed for" guy.

Fatigue shouldn't be much of an issue here unless the gun is built crazy close to failure anyways. I mean, how many folks are going to put 10,000 shots through their guns?
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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: jackssmirkingrevenge » Thu Mar 30, 2017 6:10 am

how many folks are going to put 10,000 shots through their guns?


... which raises an interesting question, do you have a shot count for VERA to date?
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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: jrrdw » Thu Mar 30, 2017 4:00 pm

jackssmirkingrevenge wrote:
how many folks are going to put 10,000 shots through their guns?


... which raises an interesting question, do you have a shot count for VERA to date?


More then we should have missed ! :cry:
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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: D_Hall » Thu Mar 30, 2017 9:17 pm

jackssmirkingrevenge wrote:
how many folks are going to put 10,000 shots through their guns?


... which raises an interesting question, do you have a shot count for VERA to date?


Haven't kept rigorous records, but probably on the order of 50.

Things have been looking up though. VERA represented a capability that was pretty radical compared to the other research guns out there. As such, it was a market looking for customers. Word spreads slow. Money spreads even slower. After all, people have to find out about VERA, realize what it means for their program, write a proposal to get funding to do whatever test they had in mind, actually *get* the money..... Yeah, it was probably 3 years before VERA actually had a paying customer, but in the past year or two things have been speeding up (yeah!).
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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: jackssmirkingrevenge » Fri Mar 31, 2017 6:09 am

Haven't kept rigorous records, but probably on the order of 50.


Given that every firing is an "event", that's quite a decent number nonetheless.

but in the past year or two things have been

(•_•)

( •_•)>⌐■-■

(⌐■_■)

speeding up

(yeah!)


Still waiting for the day a customer pulls out at the last minute, you have the thing all fueled and ready to go and there's a sack of potatoes handy, leading you to create the world's largest spud shotgun.
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Re: Hybrid Wiring Outside to Inside of Chamber

Unread postAuthor: Zeus » Tue Apr 18, 2017 9:33 pm

Can I just throw something out there, those boost converters actually have quite a good lifespan, if you operate them at the correct voltage. 9v is far too much, they specify 3-6v, so use it. Besides how long are you holding down the trigger for...

Not to mention the ridiculously short lifespan of cheap stun guns, they tend to use a spark gap versus solid state switching.

And another vote for the spark plugs
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Re: Hybrid Wiring Outside to Inside of Chamber

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