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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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Unread postAuthor: Technician1002 » Sun Jun 09, 2013 12:16 pm

Just for grins, play with various barrel lengths with no other changes in GGDT.
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Last edited by Technician1002 on Sun Jun 09, 2013 7:04 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Sun Jun 09, 2013 12:27 pm

Sexeh! The check valve wasn't really necessary since the piston isn't o-ringed, but nice touch :) I wouldn't be surprised if your golf balls come close to the speed of sound at high pressure.

What will you be using as a bumper? Even a light piston needs to be buffered somehow.
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Unread postAuthor: gyrotech » Sun Jun 09, 2013 3:45 pm

Big fat o ring glued with a rubber like glue.
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Unread postAuthor: Technician1002 » Sun Jun 09, 2013 6:48 pm

You will want more bumper. The deceleration zone of piston movement should be at least 1/2 as long as the distance it travels to pick up speed.

Force = Mass X Acceleration. Slowing a piston in 1/10th the distance it had to pick up speed has an average force of 10X the force accelerating. Peak forces if the slowing space is non linear can be much higher.

This is the principal used to drive nails. You can't just shove a nail into an oak plank, but using a hammer, it is easy to push it all the way in. This type of forces unchecked will destroy the piston bumper interface if it is not properly built in high power launchers.


In summary, make the piston travel with a space to rapidly pick up speed, then another area long enough to safely slow the piston back down to a stop to keep the forces below destructive levels. Failure to design this has lead to many piston and housing failures. At high pressure, safety becomes an issue.

The bumper in my ABS Apple cannon is as long as the piston. It can be seen below right behind the golf ball. Before the upgrade the piston used to blow out the breech requiring several rebuilds.
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Damage from inadequate bumper.
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I start to slow the piston down slightly before it has reached 3/4 full open so it is slowing the last part of fully opening, through full open then additional space is provided just beyond fully open into the pilot to cushion the stop.
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Unread postAuthor: gyrotech » Sun Jun 09, 2013 8:32 pm

The piston bumps a 1/4" thick rubber oring. The oring sits against 1" thick aluminum. The 1" thick aluminum is bolted with 8 bolts, each 5/16" thick.

The piston is made from UHMW. Ultra High Molecular Wear. You can smash this "plastic" stuff with a hammer all day long. It will not shatter. It might deform a little.

With the design the way it is, there is no room for a slowdown area. I might be able to add in a 1/2" thick felt bumper. Not sure if that would really help nor be necessary.

One way I can think of, to make the impact less. Decrease the weight of the piston. I might be able to mill out some of the material, making it lighter.
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Unread postAuthor: Technician1002 » Sun Jun 09, 2013 9:29 pm

The problem with a 1/4 inch O ring is it can compress no more than 1/4 inch. This is your maximum deceleration distance. Limiting it's total travel distance does limit the maximum speed it can reach while opening which will help a lot.

I've not had much luck with fiber material for a bumper. I tried some wall to wall carpet and it was rapidly torn to dust. You need a material that can deform without tearing apart.
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Unread postAuthor: gyrotech » Sun Jun 09, 2013 9:46 pm

The piston can only travel 1.75", which is all it needs to travel for full air flow.
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Unread postAuthor: jackssmirkingrevenge » Sun Jun 09, 2013 11:43 pm

gyrotech wrote:The piston is made from UHMW. Ultra High Molecular Wear.


*Weight

You can smash this "plastic" stuff with a hammer all day long. It will not shatter. It might deform a little.


Yep, pretty hardy stuff. You should be fine.

I would trim out the piston to some extent, to maximize performance and minimize impact energy.

Here's a shítty artist's impression of what it might look like :)
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Unread postAuthor: gyrotech » Thu Jun 13, 2013 11:07 pm

Put the piston on a diet. Built a control box. Hooked up my 12volt viair air compressor to the truck for portable air. Installed two solenoid valves on the pilot air of the qev which actuates the piston valve....Made a tripod... I'll just get to the pictures. :)


Image
(I since shortened the red 1/4" tube. no more kink)

Image

Image

First toggle button: Power

Second, relay to solenoid which lets you fill the chamber

Third, Arms the big red button

Big red button, Do I really have to say what the big red button does :)

Also features a volt meter and chamber pressure gage

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Image

Image

Notice the two solenoid valves. One to fill, one to release.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 13, 2013 11:20 pm

Oh my... fantastic!

I especially like your elevation locking mechanism for some reason :)

Come on, let's see this thing in action!

By the way, I hope you'll have it securely anchored to the ground, because recoil is going to be pretty sharp...
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Unread postAuthor: mattyzip77 » Thu Jun 13, 2013 11:40 pm

Dammmm. I just got spud wood!!!!!!!!
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Go Bruins!!!!
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Unread postAuthor: gyrotech » Fri Jun 14, 2013 5:17 am

jackssmirkingrevenge wrote:
By the way, I hope you'll have it securely anchored to the ground, because recoil is going to be pretty sharp...


I might bring a couple camping pegs and some straps :)

Trying it out tonight at a friends bawn fire birthday party thing.
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Unread postAuthor: gyrotech » Sat Jun 15, 2013 12:52 pm

Just running off a friends air compressor yesterday. 100psi line pressure.

Shot a couple bags of taters sky high. Golf balls at 100psi, I could barely see them go, barley... I mean I think I can see them. Wow.

[youtube]http://www.youtube.com/watch?v=7cMbb3pYdxQ[/youtube]

Shooting and firing is very easy. Using the control box, after you have loaded your projectile, just walk away and initiate sequence. So easy.

More vids to come. I didn't do all the filming so I'm waiting on a usb stick :)

I believe an auto loader and a green laser dot sight is in the future of this gun. Definitely the green laser, thats for sure.
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Unread postAuthor: wyz2285 » Sat Jun 15, 2013 2:07 pm

ever considered a recoil system? I made one for my hybrid and it's awesome to see it fire.
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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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Unread postAuthor: jackssmirkingrevenge » Sun Jun 16, 2013 12:09 am

wyz2285 wrote:ever considered a recoil system? I made one for my hybrid and it's awesome to see it fire.


+1

I couldn't really focus on the c(.)ntr(.)l box

:D
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