11 replies to this topic

[Gyrvalcon]

I've been in the early stages of making my first compressed air homemade for too long now, and I approach NH with questions and a sense of apprehension. I'll start with what I have: vague plans and failed attempts.

The Vague Plan:

A valve inspired by Dr. Nerf and his valve and CaptainSlug's A.B.P.



I had first hoped that the barrel's back-and-forth motion would correspond directly with the trigger pull and return. Unfortunately, my first iteration proved that this would require a trigger pull of several inches: the dart length + dead space between dart and valve + valve travel.

Which brings me to...

The Failed Attempt:

My first iteration went undocumented, as I abandoned the project after hitting some problems. I can, however, give a description and illustration.



1.
-The "Outer Barrel" is the long beige rectangle, with the right angle at the end, made of 3/4" CPVC
-The "Reservoir" is the grey rectangle, made of 1" PVC
-The "Connection" between the Outer Barrel and Reservoir is 1/4" Vinyl Tubing
The "Valve" is the more complex part, descibed further in (2.)

2.
-The Valve consists of two O-Rings on a section of Threaded Rod, spaced by 1/2" CPVC and kept in place by two Nuts that have been ground down to fit inside the Outer Barrel.

This model failed because of bad seals between:
-The "Air Source" (not pictured) and the Outer Barrel
-The Reservoir and the Outer Barrel, at the Connection

Mistakes/Problems To Be Solved:
-I sealed the Connection with only hot glue, and expected it to be airtight.
-I didn't use a one-way valve between my Air Source (a hand pump) and the Outer Barrel.
-Where the Connection met the Outer Barrel, there was too much obstruction, keeping the Valve from sliding freely.


That should sum up what I've done so far. I've now been motivated to take another crack at it, but I'd like to run few ideas past the NIC. First, the Connection between the Outer Barrel and Reservoir. The "two crappy bits of tube and hot glue" approach was a bad one. Hot glue isn't durable, so I got some PVC cement, which means no more vinyl tubing. I need a Reservoir and Connection that's airtight and makes no protrusion into the Outer Barrel, so as to keep the Valve's movement unimpeded, yet allow maximum airflow when open. Second, I've realized I need a one way valve between the Air Supply and the Outer Barrel, as the pump isn't enough to hold back the pressure needed. I bought a couple Schraeder valves, but I need to find the best way to mount them. The valves are encased in rubber... and I kind of lost the little documentation they came with...has anyone used these before?

The Schraeder Valve:


The last problem, one which I haven't played with yet, is the best way to trigger the valve. If plain trigger pull is insufficient, then there needs to be a different way to cycle the action. I, of course, am leaning towards lever action. I'm shying away from a pneumatic ram (like in the A.B.P.) due to complexity issues. Ideas?

I hope I've explained the situation perspicuously, If you have questions, ask away.

Edited by Gyrvalcon, 22 July 2007 - 12:13 AM.

[The Crackerjack Man]

I hope you can get this gun to work. And as for a way to put that valve in. Drill a hole in the end cap of your airtank. Thats what i've done forever and I use those same exact valves that you have in the picture.

[Gyrvalcon]

Do I need to use anything else to seal the hole, or is the rubber enough of a seal?

[The Crackerjack Man]

Do I need to use anything else to seal the hole, or is the rubber enough of a seal?

I use glue. Just make sure the hole isn't to big for the valve, make it so the valve is alittle tight to slip in. And then glue in. I use plumbers goop or something along the lines of that.

[Flaming Hilt]

I always use Super Glue when I want airtight things, do just what he said (a little tight), then drag or blow a drop or two around the circumference of the seal. It needs a half a day to dry though, as it'll be thick.

You could try putting the valve to a ninety degree angle of the barrel.
...with that setup you may even be able to make it semi-auto with some leverage tricks. Making a triangle with your trigger on a short angle (IE 35) and your valve attachment on a large angle (IE 55)... and for maximum leverage you'd want to change the IEs so at full trigger stroke it'd be a 45-45-90 triangle.

[bored kid93]

Hmm, is this going to use a pilot valve? A schrader valve in my opinion would be kind of annoying, since you would have to lug a bike pump every where. I like your design, it's quite impressive, I must say. Maybe I could help a bit with this, cause it's got my interest.

Edited by bored_kid93, 22 July 2007 - 12:23 PM.

[Thom]

Carrying a small bike pump isn't a problem – it can be just a little bigger than a built-in pump.

[Gyrvalcon]

You could try putting the valve to a ninety degree angle of the barrel.
...with that setup you may even be able to make it semi-auto with some leverage tricks. Making a triangle with your trigger on a short angle (IE 35) and your valve attachment on a large angle (IE 55)... and for maximum leverage you'd want to change the IEs so at full trigger stroke it'd be a 45-45-90 triangle.

This is an excellent idea, and one that I hadn't thought of previously. It brings up a new problem however: How to actuate the valve if it's on an angle. That would probably introduce a new seal into the equation.
And Seals Are A Bitch.

[General Cole]

My ideas.
1. Attach the trigger to the piece and use some sort of cord on little block and tackles to pull the breach.
2. Use the block and tackle idea to do both.

After you put in the vinyl tube take a long drill bit and drill out what protruds into the outer barrel. I think that those schrader valves were used in CX's homemade in the homemades section.

Edited by General Cole, 22 July 2007 - 11:47 PM.

[Gyrvalcon]

My ideas.
1. Attach the trigger to the piece and use some sort of cord on little block and tackles to pull the breach.
2. Use the block and tackle idea to do both.

After you put in the vinyl tube take a long drill bit and drill out what protruds into the outer barrel. I think that those schrader valves were used in CX's homemade in the homemades section.

*snip*

I wasn't clear enough with my original plan, I suppose. The beauty of the action in the first diagram is that the Inner Barrel can push the Valve back, and because the Inner Barrel is not sealed for its whole length, the trigger can attach at some point on it.

As for the Reservoir, I thought of something that I'd like to run by you all. If the Reservoir was wrapped all the way around the Outer Barrel, I wouldn't need to worry about protrusions into the Outer Barrel. It would be a question of making an air-tight seal at the hole through the 1" PVC endcaps.

[Flaming Hilt]

You could try putting the valve to a ninety degree angle of the barrel.
...with that setup you may even be able to make it semi-auto with some leverage tricks. Making a triangle with your trigger on a short angle (IE 35) and your valve attachment on a large angle (IE 55)... and for maximum leverage you'd want to change the IEs so at full trigger stroke it'd be a 45-45-90 triangle.

This is an excellent idea, and one that I hadn't thought of previously. It brings up a new problem however: How to actuate the valve if it's on an angle. That would probably introduce a new seal into the equation.
And Seals Are A Bitch.

Well. Didn't I just say. Make a nice little triangle. Ahm. Wait for it...


Just replace "Valve" with what you had in mind. As for the seal in the back, use an O-ring one size smaller than the rod you use to control the valve, and it should be fine. I dun it.

EDIT: Disclaimer: Not drawn to scale. ; o)

Edited by Flaming Hilt, 23 July 2007 - 11:51 AM.

[Gyrvalcon]

Well. Didn't I just say. Make a nice little triangle. Ahm. Wait for it...

*snip*

Just replace "Valve" with what you had in mind. As for the seal in the back, use an O-ring one size smaller than the rod you use to control the valve, and it should be fine. I dun it.

Yes, that would solve the trigger pull problem, at the expense of adding another seal. I'm not sure which road I'll take yet.