14 replies to this topic

[frigginninja]

Hey guys, does anyone know about how much psi is needed for a somewhat powerful homemade gun? I need to do calculations and stuff, but I realized I didn't have a pressure goal. The barrel will be 1/2" PVC and not terribly long. Thanks

[The Inventor Guy]

40 Psi - 60 Psi usually works well. It depends on the size of the air tank.
If you're using a 1" x 12" air tank, 60 Psi should be good enough.
Be careful though, the larger diameter of the tank means it will explode when it gets to the same amount of pressure a smaller tank would. For example, a 2" x 12" tank might explode when it reaches 100 Psi (I don't know if it actually would, I'm just using it for an example) whereas a 1" x 12" tank might take 120 Psi ; 70 Psi for a 2" diameter tank would be as much as you need it. 90 Psi would be as high as you should go for safety reasons. For the air tank/barrel scale, use a pipe double the diameter of the barrel and make it half the length of the barrel. This should give the air tank the smae volume as the barrel which means you won't need to pump it as much to get a good amount of air/pressure to launch the dart well.

These examples are set for a single-shot homemade.

-TIG.

[cxwq]

The best predictor of someone being a self-important asshat happens to be the abuse of colored text.

Just so you know.

[The Inventor Guy]

...
I'm not a n00b or a newb, I've been around NHQ for a while.
If you don't want me to use coloured text, just tell me not to.
I don't intend to sound like a smart-arse or 'self-important', I just tried to provide some information which was asked for.

Sorry.

-TIG.

[AirApache]

...
I'm not a n00b or a newb, I've been around NHQ for a while.

And there ya have it, folks!

I don't think Cx was saying that your advice was bad. I think that he doesn't want the users of his site to frequent in epilepsy and seizures, which often leads to, in a long run, neural damage or death.

Oh, and also that your head is the size of Toronto.

Ok maybe that's not exactly the reason...

Edited by AirApache, 22 September 2004 - 02:49 AM.

[frigginninja]

Thanks for the advice, it should come in handy. I'm planning something that would be pretty interesting if it worked out.

Can anyone tell me the disadvantages of ball valves? I've heard a few people say they don't like them, and I was wondering why.

[NinjZ]

Some people just prefer to use a hose nozzle instead for a more gun-like feel. Plus its easier to use than a ball valve. It depends on the design of your homemade and what will fit best.

[xedice]

Ball valves are manually opened very slowly and unevenly.
Pros of a ball valve: cheap, simple.
Cons of a ball valve: slow and uneven open of air, aesthetically unpleasing, lack of a gun trigger feel

[frigginninja]

For the air tank/barrel scale, use a pipe double the diameter of the barrel and make it half the length of the barrel. This should give the air tank the smae volume as the barrel which means you won't need to pump it as much to get a good amount of air/pressure to launch the dart well.

Thanks. Oh yeah, I saw that one of the home-mades uses a garden hose handle. Has anyone tried this, and if they have, did it work well? It looks like it could be pretty good, if it released the air fast enough.

BTW, not meaning to be an ass, but a cylinder with twice the diameter and half the length of another cylinder also has twice the volume, not the same volume. My major makes me picky about these things

[GeneralPrimevil]

...a cylinder with twice the diameter and half the length of another cylinder also has twice the volume, not the same volume.

In support of your statement, here's some basic PVC tank sizes. For the point of anyones interest, the math is included.
Volume of a cylinder is (pi)r^2(H). r equals .5 inches, and h will equal 20 inches.
(pi).5^2(20)=(pi).0625(20)=15.7079etc. cu. in.
Now, r will equal 1 (for radius of 2 inch PVC), h will equal 10.
(pi)1^2(10)=(pi)1(10)=31.4159etc. cu. in.
15.7079etc(2)=31.4159etc.
There ya go, frigginninja was indeed right. TIG, I've read some you're posts at NHQ and I thought that you knew that as well.

Now, on a side note, for distances/velocities you will have to take barrel diameter and the area of dart that is hit by pressurized air. What I mean by that is if you cut/melt a cone-shaped section into the back of the dart, you increase the surface area of pressurized air hitting the dart. It works very well with mega stefans because you can get about 1.25 sq. in. on the back of that dart, which means that, with an airtank at 25psi, 31.25 pounds of pressure is hitting that dart. Just good luck getting the cone to have that big an area of impact. Someone could use Newton's Second Law and figure out just how fast the dart would be going, just be sure to reduce the velocity with air and barrel friction.

[The Inventor Guy]

Mmm...Pi...
Oops! I meant to say twice volume. Sorry, I was thinking twice but typed same for some reaon. I thought I wrote twice, but reading it now it seems I thought it was the same volume, but really I know it would be twice the volume.
I've made a homemade with the hose handle for the trigger and it works well. It's easier to control and gives it a..uh...trigger..feel.
I'll find the link for my Topic at NHQ n a sec.
EDIT: Here we go. If some of the pics don't show, just find the link to the pics in properties and go to that link. You should only have to do it to n pic for the rest to come up.

-TIG.

Edited by The Inventor Guy, 26 September 2004 - 09:18 PM.

[frigginninja]

Thanks a lot TIG, but I don't see a link or anything

[The Inventor Guy]

If the picture isn't showing;
-Right click on the pic
-Go into 'Properties'
-Copy the URL of the Pic
-Then paste it into the address bar of your web browser.
Then you'll go to a page which shows the picture

-TIG.

Edited by The Inventor Guy, 27 September 2004 - 08:16 PM.

[GeneralPrimevil]

Mmm...Pi...
Oops! I meant to say twice volume. Sorry, I was thinking twice but typed same for some reaon. I thought I wrote twice, but reading it now it seems I thought it was the same volume, but really I know it would be twice the volume.
I've made a homemade with the hose handle for the trigger and it works well. It's easier to control and gives it a..uh...trigger..feel.
I'll find the link for my Topic at NHQ n a sec.
EDIT: Here we go. If some of the pics don't show, just find the link to the pics in properties and go to that link. You should only have to do it to n pic for the rest to come up.

-TIG.

Hmm...

I don't see a link or anything

Couldn't have put it better.
Is this the thread with the hosehandle homemade you were talking about?

[frigginninja]

That's awesome, I think I'll try that. Thanks for the link, GP.

I know this should go in homemades forum, but what is good to use for lubrication when making a plunger? I would like it to be reeeeeeeally airtight if possible. And does plumber's goop adhere to metal at all?

Edited by frigginninja, 30 September 2004 - 07:47 AM.