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Custom Aluminum Pneumatic Build

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: Labtecpower » Fri Dec 13, 2013 4:21 am

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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: jackssmirkingrevenge » Fri Dec 13, 2013 5:46 am

Fantastic Aluminium Pneumatic, Fantastic Aluminium Pneumatic, Fantastic Aluminium Pneumatic, Fantastic Aluminium Pneumatic?
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: gyrotech » Sun Dec 15, 2013 12:33 am

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Home position:
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Recoil position:
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More to come. :bounce:
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: jackssmirkingrevenge » Sun Dec 15, 2013 2:36 am

Oh yes...

What will you be using as a buffer/return system? hydraulic, pneumatic, springs, bungee chord?

These sort of things are handy and cheap: http://www.monroe.com/en-US/products/Ma ... t-Support/
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: gyrotech » Sun Dec 15, 2013 10:40 am

I'm thinking springs will suffice. I was going to coil up my own from some stainless steel wire. Can't really be sure how how much spring pressure I need until trying.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: Ragnarok » Sun Dec 15, 2013 3:25 pm

gyrotech wrote:Can't really be sure how how much spring pressure I need until trying.

The necessary spring rate is easy enough to estimate.

Momentum is conserved, so the momentum of the launcher is the negative of the momentum of projectile and the gases.

We can easily estimate the momentum of the projectile - use GGDT to model for the highest pressure and heaviest projectile intended, then multiply velocity by the mass of the projectile to get its impulse.
The momentum of the gases is a little less certain (particularly with a muzzle brake), but the upper limit on their velocity can be assumed to be the ambient speed of sound. Their mass is relatively easy to estimate - 1.2 to 1.3 grams per litre per atmosphere.

From there, we can work out the momentum of the launcher. Divide this by the recoiling mass to get the recoiling velocity, then plug that all back into "half mass times velocity squared" for the recoil energy.

The energy stored in a spring is... well, basically the same equation. Half the spring rate times the compression distance squared. If precompressed, this is increased by the precompression force times the additional compression distance.

You want to make sure that at maximum compression, the spring rate is high enough to absorb at least as much energy as the maximum recoil energy of the launcher, or else they'll bottom out.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: wyz2285 » Sun Dec 15, 2013 3:33 pm

Shame it's just a pneumatic! A muzzle flash would be more suitable rather than a cloud of vapor... Just imagine firing it at night.
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Re: Custom Aluminum Pneumatic Build

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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: gyrotech » Sun Dec 15, 2013 3:39 pm

Hour of calculations. Make a few springs. Build device to measure spring rates. Adjust method of building springs until proper spring rate is acquired.

Or.

Make a spring.Try it. Adjust rate if needed.

There's two ways to build things. Calculate the hell out of it. Build by the seat of your pants. I have a lot of experience building by the seat of my pants. Given this is just a spring and as big of a deal as e.g. chamber volume, I'll just go for it :mrgreen:

Ragnarok wrote:
gyrotech wrote:Can't really be sure how how much spring pressure I need until trying.

The necessary spring rate is easy enough to estimate.

Momentum is conserved, so the momentum of the launcher is the negative of the momentum of projectile and the gases.

We can easily estimate the momentum of the projectile - use GGDT to model for the highest pressure and heaviest projectile intended, then multiply velocity by the mass of the projectile to get its impulse.
The momentum of the gases is a little less certain (particularly with a muzzle brake), but the upper limit on their velocity can be assumed to be the ambient speed of sound. Their mass is relatively easy to estimate - 1.2 to 1.3 grams per litre per atmosphere.

From there, we can work out the momentum of the launcher. Divide this by the recoiling mass to get the recoiling velocity, then plug that all back into "half mass times velocity squared" for the recoil energy.

The energy stored in a spring is... well, basically the same equation. Half the spring rate times the compression distance squared. If precompressed, this is increased by the precompression force times the additional compression distance.

You want to make sure that at maximum compression, the spring rate is high enough to absorb at least as much energy as the maximum recoil energy of the launcher, or else they'll bottom out.


Your smart, grounded. What do you do for a living?

wyz2285 wrote:Shame it's just a pneumatic! A muzzle flash would be more suitable rather than a cloud of vapor... Just imagine firing it at night.


You should see the vapor cloud if you pour a little bit of water into the chamber before compression. It's nuts! I'll have to do a video on that.
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Last edited by jrrdw on Sun Dec 15, 2013 3:46 pm, edited 2 times in total.
Reason: Double post.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: wyz2285 » Sun Dec 15, 2013 3:40 pm

Why not use pneumatic cylinders and just adjust the pressure?
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: gyrotech » Sun Dec 15, 2013 3:41 pm

wyz2285 wrote:Why not use pneumatic cylinders and just adjust the pressure?


Overkill. I mean... This whole cannon is overkill. Gotta stop somewhere.

Not just that. 1 or 2 psi might be so much pressure that it doesn't recoil.

PS, love the sig.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: wyz2285 » Sun Dec 15, 2013 3:50 pm

I used a pneumatic cylinder for my .50 cal hybrid, the cannon is tiny compared to yours and it still kicks hard dry fire at mix10.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: Ragnarok » Sun Dec 15, 2013 6:09 pm

gyrotech wrote:Build device to measure spring rates.

The maths for estimating spring constant is actually relatively trivial. A spring is loosely described as a coiled lever acting on a torsion bar, so it's not hard to work out from the shear modulus and dimensions of the spring.

Or, in other words: Do five minutes of maths. Build the right spring first time. :tongue3:

Your smart, grounded. What do you do for a living?

I'm actually undead. But my main income comes from being an artist.

1 or 2 psi might be so much pressure that it doesn't recoil.

245 psi in a 1.7" barrel is producing in excess of 500 lbf pushing the launcher back, so it'd take a very large pneumatic cylinder for only a couple of psi to stop it recoiling.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: jackssmirkingrevenge » Sun Dec 15, 2013 8:55 pm

I still think a small gas spring would be a good idea - they are cheap, simple to install and will dampen the recoil more effectively than a coil spring - plus they are available in a bewildering variety of sizes:

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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: gyrotech » Thu Dec 19, 2013 10:17 pm

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The bolts on the end are just temporary. Will put something nicer on there shortly. Spring weight, I'm guessing it takes 50lbs to compress the full 4" of stroke. Not sure.
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Re: Custom Aluminum Pneumatic Build

Unread postAuthor: wyz2285 » Fri Dec 20, 2013 5:31 am

Nice! I actually like the bolt hehe
Now all you need it's a solid bad ass support
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