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Damage challenge

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: Gippeto » Fri Apr 10, 2009 1:23 am

About the pneumatic vs hybrid thing. I thought it would be different since pneumatics force the air through a narrow valve instead of a huge, instant dump.


Not all pneumatics are created...equal. :)

It was DYI's sctbdcV1.5 that first (to the best of my knowledge) put "daylight" through steel plate.

http://www.spudfiles.com/forums/sctbdcv ... 12103.html
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Unread postAuthor: Ragnarok » Fri Apr 10, 2009 9:02 am

Moonbogg wrote:The sabot with dart sounds excellent. 1/4" steel plate sounds like a good challenge.

Depends on what challenge you're looking for, because I reckon it can be done with a lot less energy than most people seem to think.

I still intend to get a clean hole through 1/4" steel myself (for an added challenge, I hope to be no closer than a quarter mile from the plate when I fire, but that's just my nuttiness) - I think it can be done with under 400 ft-lbs, as long as the projectile design is right.
After all, Nova managed to get to see light through a 5mm steel plate with his tiny Brass Bruiser (which I believe was considerably below 200 ft-lbs). It wasn't quite complete penetration, but there was a hole from one side to the other.

That's the issue here. You can make it a challenge to do it with power and a poor projectile design - or you can do it with a good projectile design and relatively low power.
Without a defined projectile design, it is therefore no real proof of anything greater than modest power.

~~~~~

On the note of the pneumatic vs. hybrid thing, pneumatics need not have any problem forcing the air through a narrow valve - valves can be of an equal or greater diameter than the barrel, so the flow restrictions at the valve can be minimal.
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Unread postAuthor: Moonbogg » Fri Apr 10, 2009 12:36 pm

Ragnarok wrote:Without a defined projectile design, it is therefore no real proof of anything greater than modest power.

~~~~~

On the note of the pneumatic vs. hybrid thing, pneumatics need not have any problem forcing the air through a narrow valve - valves can be of an equal or greater diameter than the barrel, so the flow restrictions at the valve can be minimal.


Totally true. I see your point. So hybrid vs pneumatic, it seems that what it comes down to is simply pressure. If all else is equal, then its just whichever has more PSI behind it. You can get that PSI in different ways. You can use the energy of an electrical compressor to create the pressure, or the energy released from the explosion by the propane. It could also be your own energy by using a bike pump to create the PSI pneumatically.
Kind of interesting here as I sought to find distinct differences but now they seem indistinguishable in some ways. I love this hobby.
When I excitedly tell people I finished a high end spud cannon, they tend to look at me like I have brain damage. If only they knew.
Anyway, I am likely going out today to make a video. I've decided not to spend any money on targets as i've already killed myself building this thing as it is. I am going to just blow the hell out of stuff and have fun. I want to make a sweet video with tight music. :D :D
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Unread postAuthor: Ragnarok » Fri Apr 10, 2009 1:00 pm

Moonbogg wrote:So hybrid vs pneumatic, it seems that what it comes down to is simply pressure. If all else is equal, then its just whichever has more PSI behind it.

Not quite. The limited speed of sound in the pneumatic cannon does slowly begin to limit efficiency as velocity begins to progress over half the speed of sound - and faster than around 80% of the SOS is still a pretty hefty achievement.
Hence, overly light projectiles are going to lose power

However, dependence on the combustion gas temperature with a hybrid, means that heavy projectiles that accelerate slowly will cause the loss of gas temperature, and thus pressure.
Hence, overly heavy projectiles may lose power.

It's a similar tendency to air rifles, where the springers (which use gas heated by rapid compression, making them similar in ways to a combustion or hybrid) tend to shoot the light pellets more energetically, and the PCP rifles tend to do better with pellets with some more mass in them.

The exact effect of each is a little hard to know. I've been working on doing analysis of pneumatics and mass vs. velocity. For my cannons at least, it seems to hold to the rough rule that up to about ~70-80% of the SOS (and at a given pressure), Mass x Velocity<sup>2.5</sup> is pretty constant. After that, the numbers start to fall away due to losses near the speed of sound.

I haven't a hybrid to analyse, but I may at sometime do some estimation with HGDT and try and find out if there's a similar work from that.

I love this hobby. When I excitedly tell people I finished a high end spud cannon, they tend to look at me like I have brain damage. If only they knew.

I've had that a couple of times - the famous "You build spudguns?" look.
This is often followed with the "Wait, that's what you mean by spudgun?!?" look.
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Unread postAuthor: King_TaTer » Fri Apr 10, 2009 10:19 pm

Moonbogg wrote: I love this hobby.
When I excitedly tell people I finished a high end spud cannon, they tend to look at me like I have brain damage. If only they knew.


Haha. I know exactly what you mean. This has happened to me on more than a few occasions. I've noticed that using the term "air cannons" seems to captivate people better. As most of us know spud guns usually carry the stereotype of taped together cans or something you build out of PVC laying around, mess with it for the weekend, then toss it in the shed. Or, worst case scenario the person has never heard of one, which then requires you to purge an explanation. Because of this I prefer to wait and show them what they do and ask questions later. :D

On topic: I haven't worked with hybrids or with high power pneumatics at all, so your better off sticking with Rag's theory rather than my guess. He always seems to sum things up in one big nutshell for us to enjoy. Well... maybe not always. :P
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Unread postAuthor: starman » Sat Apr 11, 2009 2:05 am

Moonbogg wrote:I love this hobby.
When I excitedly tell people I finished a high end spud cannon, they tend to look at me like I have brain damage. If only they knew.


I have found people who have no clue what they are to be mildly interested or mostly ambivent about them when just talking about them. The excitement really only comes when they witness their usage in person. They also tend to be a real chick magnet in the right setting... :wink:
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Unread postAuthor: CpTn_lAw » Sat Apr 11, 2009 7:25 am

Lol SOOOO true!!!

To come back to the "challenge"...A hardware store nearby sells small titanium screws, they could be used as AP projectiles.
I'd like to add that a larger cannon with a heavier, slower projectile might have the same chances of piercing a 1/4" steel plate than a small cannon with light and extremely fast projectile.
I've seen my penumatics pierce 1" pine wood with difficulty where the combustion with a AP round completely bursted it. I might enter the contest as soon as my exams are behind me, in a month. I have the firm intention to build a small caliber hybrid (probably .177). Voila!
As soon as damage pics are posted i want to see them!!!!!!
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Unread postAuthor: Moonbogg » Sat Apr 11, 2009 10:17 am

I will also be doing accuracy tests with golf balls shooting at things like soda cans at distances that would be unmanageable without a good laser sight and solid gun design. That would be so sweet to actually have power that you can aim and control at small targets at a reasonable distance. Thats what I am going for (with golf balls at least).

I also found an old toaster oven that will soon have its end recorded on video :twisted: :twisted: :twisted:
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Unread postAuthor: SpudFarm » Sat Apr 11, 2009 11:03 am

steel plates is not that hard to penetrate gippeto, i did it with my marble pneumatic, the projectile was a 3mm thick tungsten rod.


the real hard thing is sand! if you penetrate 12" of sand you could be proud i think.
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Unread postAuthor: Ragnarok » Sat Apr 11, 2009 12:23 pm

SpudFarm wrote:the real hard thing is sand! if you penetrate 12" of sand you could be proud i think.

Well, if you're so convinced that sand is so tough, try getting through the same distance of steel plate then. :tongue3:

Yes, sand stops bullets and projectiles generally within about six inches - but I've also seen a video of a bullet going through 18" of ballistics gel, then 2 feet of packed wet sand, and still going like a bat out of hell after that. I'm sure you can guess the cartridge involved.

But, for a given overall thickness, I think steel is as tough as we need bother with. However, if you managed to go through 1/4" steel with a marble calibre pneumatic, I may need to up the ante for my project.
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