My new (mini) air cannon

[Energy84]

I've been busy in the shop lately, working on my latest creation. My miniature version of Glen Shindel's <a href="http://www.spudzooka.net" target="_blank">Spudzooka</a>. It's 13.5" long, has a 12.25" barrel bored to .68 (paintball caliber :D ) and has a 13" by 2" chamber.
Sorry about the poor quality pics, but I just couldn't pass up the price on the camera <img border="0" title="" alt="[Wink]" src="wink.gif" />

<img src="http://www.boomspeed.com/energy84/RearViewOpened.gif" alt="" /> This is the rear of the cannon, opened up so that you can see the diaphragm and the endcap. Note: If you look very closely, you can see the o-ring in the endcap that seals everything up.

<img src="http://www.boomspeed.com/energy84/InsideCloseUp.gif" alt="" /> This is the inside of the cannon.

<img src="http://www.boomspeed.com/energy84/DiaphramSide.gif" alt="" /> This is the diaphragm, the only moving part. It is made out of aluminum. I originally planned on putting two o-rings (hence the groves in the side) to seal it and force it to move, but the o-rings proved to be too tight and the cannon would not fire. So instead I put a short length of small braided rope into the rear groove and now it slides, and seals, perfectly.

<img src="http://www.boomspeed.com/energy84/DiaphramTopCloseUp.gif" alt="" /> Here is the top of the diaphragm. Those two holes are to allow the air to flow by into the chamber. You can clearly see the imprint left in the gasket from the back of the barrel. The gasket itself is just some hotglue that I slowly melted into the bottom of the diaphragm.

I'm very happy with the performance that I'm getting. Although I haven't actually measure my distances, with a 3/8"x1"long bolt I'm getting about 200yards@75PSI.
The cannon has been pressure tested and leak tested to 150PSI but I'm confident that it is capable of at least 250PSI. I just haven't been able to find a compressor to match yet :(

Edit: Changed image server

<small>[ June 10, 2002, 09:09 PM: Message edited by: Energy84 ]</small>

[kingspaz]

the pics are dead. be careful with high pressures as you'll have one hell of a pipe bomb on your hands!

edit: pics seem to be working now......maybe my computer was fucking up again :confused:

<small>[ June 07, 2002, 06:45 PM: Message edited by: kingspaz ]</small>

[Spudkilla]

IN the topic of cannons, has anybody EVER tested to see if piston was better than diaphragm, or the other way around? I've never heard of it, and I don't have the time or money to do it. By the way, I've got an over-under sprinkler valve cannon, and two "grape-shooter" cannons.

[Energy84]

I have thought about building a cannon using a piston instead of a diaphragm but figured that it'd be more complicated and thus harder to build. I might however try to build one. I think that it'd be a good project, but I'm not convinced that there would be any big performance gains. The beauty of the system that I'm using is that the air behind the diaphragm is vented almost instantaneously and once it's gone, the diaphragm moves with around 500lbs of force. Considering that the diaphragm only needs to move about 0.25" to be full open, I think that this is about as fast as you'll ever be able to open a valve. (Do the math if you want, but it's 3:30am and I'm half pissed, so I'm not going to even bother trying).
Even though in my opinion a diaphragm system probably has better performance, the piston system is most likely more suited to larger cannons (think, pumpkin chukin').

EDIT: Typos

<small>[ June 09, 2002, 03:35 AM: Message edited by: Energy84 ]</small>

[Fl4PP4W0k]

Well... that gun up there looks to me AWFUL similar to a piston gun :p

I thought - I may be wrong - that a 'diaphragm' gun works on the principle of a sheet of neoprene\rubber being forced against the barrel and bending, allowing air to pressurize the main chamber.

Your design seems to work by forcing a peice of aluminium, with an inernal seal made from hot-glue, against the barrel as pressure is applied from behind. The air fills the forward chamber through a couple pin-holes. When you instantly empty the rear chamber, the aluminium peice is slammed backwards with the force of the forward air pressure multiplied by the area of the 'diaphragm'. Thus the air follows the path of least resistance out of the barrel - propelling the paintball at stupendous speeds towards its unsuspecting target.

Am I wrong???
If not, you have built a Piston Gun :D
BTW, I have a little 12ga PVC piston cannon, and its pretty goddamn fun.

That gun looks damn nice BTW...
l8r,
rob

[Anthony]

I'd personally call Energy84's gun a piston gun too. It looks like there's some nice machine work gone into that, I especially like the breach end barrel support :)

Most of those small car tyre inflators will do 250-300psi, their output is pretty small but it shouldn't matter too much on a gun of this size and they're pretty cheap too.

[PYRO500]

300 psi! I haven't found a portable pump that will go over 200 psi. The pumps at gas stations are usually set to something like 120 psi or lower. I'd reconsider using very high pressures in a piston gun beacuse when the pison slams into the back of the gun it could cause damage and could slam against the back of the gun and hurt you

[Anthony]

Yep, the 250psi ones are more common but I've seen a few brands that do 300psi. They're those units that run of the cigartte lighter in a vehicle.

You could always a damping material or spring behind the piston to absorb some of the recoil shock. But I'd avoid putting your body directly behind the gun anyway (I do this as a matter of habit with all spudguns).

[Fl4PP4W0k]

*chuckles*

Those $US30 Air Compressors you buy for car tyres or whatever, may have a PRESSURE gauge rated to around 200-300 psi... I have one myself.

I tried using it with a medium sized Pneumatic Cannon. It sucked donkey balls. Eventually (about a minute) it got the thing upto 100psi. *sigh*
After that, it would go up like 20psi a minute... while the motor made a sad crunchy dying noise. Fuck that.

I now use a $AU28 (about $15US) track pump, which reaches about 135psi NO PROBLEMS in about 30 seconds... with not too much effort.
(this is a VERY small chamber... :) )

So, If you have chunky ass cannon (3 or 4" chamber) then a compressor would be a good idea... as you wont strain ur precious muscles :p But for a gun of your size, a somewhat decent track pump makes MUCH more sense.

Ofcourse, having a cheap compresser permanently pressurizing either a compressor tank or old propane can would be pretty useful....

[Anthony]

I did warn that the output was rather pitful! For a 3' or 4' chamber several feet long then yeah, it's not practical to get it to 250psi, but for small volume, high pressure guns it does work. One of mine gets a 3' length of 1.25" chamer to 250psi without too much difficulty.

By track pump do you mean the stirrup types? I've got a cheapish one that goes up to 120psi nice a quickly and is great for the bigger, low pressure (100ish psi) guns.

[Fl4PP4W0k]

Stirrup... I think so.

Its a T-Style vertical one, you stand on the base. And pump the handle thingy... its not like a foot pump.

Fuck man, Ive been playing with my just-revived 12ga piston cannon. :D
At 45PSI, it shreds a coke can quite satisfactorily with a handful of screws. I fired it at that pressure, and it went thru a can and blew a ragged hole in the trash receptacle positioned behind it... then leaving a screw in the skirting board.

I found a box of Water-Color paints at the local learning institution, and the little tubes fir perfectly in my barrel :)
Time to redecorate the forementioned institution...

How cool is the Sig !!

[BrAiNFeVeR]

Isn't there something in the rules about sig lenght of max. 3 lines ?

Though it's a very nice one, I must admit ...

[kingspaz]

Fl4PP4W0k, i like the sig but it MUST be removed as there is a limit to 3 lines for sigs.

[Energy84]

I suppose you could call it a piston but I still think that it would be more appropriate to call it a diaphragm. Even though the diaphragm is shaped like a piston. The only reason I gave it the piston shape, was to prevent it from getting cocked in the barrel.
My understanding of what a piston type cannon looks like is shown in the drawing below.
<img src="http://www.boomspeed.com/energy84/Pistontypecannon.gif" alt="" />
The piston would slide inside of the rear part of the barrel and would plug all the little holes. To fire, the chamber would be pressurized while the piston is plugging the holes, then once pressurized, you would simply pull the piston back via the rod that it's attached to.
That's the theory behind it. I've been looking into it more seriously and there would be a bigger potential for leaks, but I think I could pull it off.
I've already thought of a way that I could convert my gun into a piston type, but unfortunately, I won't be able to do it until next fall since I made all this at school.
Gotta love all the free materials and equipment :p

BTW, does anybody know of a better image host?

I also setup a website which is basically just the above post. You can find it <a href="http://www.chr1s.b0x.com/Minicannon/Minicannon.htm" target="_blank">here</a>.
Unfortunately my host for this site doesn't allow outside linking <img border="0" title="" alt="[Frown]" src="frown.gif" />

<small>[ June 10, 2002, 09:10 PM: Message edited by: Energy84 ]</small>

[Devils Knight]

You can use a free host I've seen a few other member's using: <a href="http://www.boomspeed.com" target="_blank">www.boomspeed.com</a> it allow's hotlinking, but with a small limit of 1mb account's. Oh well, nothing stopping you from making several accounts.

[Fl4PP4W0k]

<img border="0" title="" alt="[Eek!]" src="eek.gif" />

Thats a piston gun !?

lol

Im not even sure what one would call a design such as that... but a piston design it aint. A piston cannon uses a free sliding piston in the rear section of the chamber, which seals against the barrel when pressure is applied - and slams back when rear chamber is vented to atmosphere.
Sounding familiar <img border="0" title="" alt="[Wink]" src="wink.gif" />

Basically, your gun _is_ a piston style - from what I can see here.
A very NICE one mind you :D

Sorry bout the sig :\
awwwww

[Energy84]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica"> A piston cannon uses a free sliding piston in the rear section of the chamber, which seals against the barrel when pressure is applied - and slams back when rear chamber is vented to atmosphere.
</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">Now go download the plans for the spudzooka 234 at <a href="http://www.spudzooka.net" target="_blank">Spudzooka.net</a> and tell me how the firing mechanism works. You'll clearly see that you have just described how it works, and that it IS called a diaphragm.
I know my pic is rough, but the idea is that when the piston is slid back, the air is allowed to rush through the holes into the barrel. I believe that this is the same system used in those big ass "Pumpkin Chuckers".
and yes, your sig is tooooo long.

I've started work on a portable airtank that is roughly twice the volume of my cannon. It will have a shraeder valve (SP?) to fill it up and a short (3 ft or so) hose to attach to the cannon. Should be fun!

Edit: Typos

<small>[ June 11, 2002, 06:18 PM: Message edited by: Energy84 ]</small>

[Anthony]

The 234 is indeed what I've come to know as a diaphragm gun. The main difference between piston and diaphragm that I have seen time and time again on various websites, is that a diaphragm mostly flexes with the changing air pressures and a piston slides back and forth. The 234 has a rigid diaphragm so it's really a bit of both.

[aussie_boy]

well i have a good one for ya a six shot cannon try going to www.Techleague.com let me know what ya think

[Skean Dhu]

i have a portable aircompressor,it has a 12V I/O port for recharging itself adn things such as cell phones. its rated up to 260 if i recall correctly. but the air flow sucks ass and take ~2min to get to 100 psi on my 3"X20" chamber. i might build a new airchamber soon , one with a PSI gauge so then i can use CO2 from those portable bke pumps that run off of 12g. canisters. or if i have the time and motivation i might rig it to use my paintball tanks

[Yorki_pyro]

Does anyone know where to find pressure rated PVc pipe in the UK? BnQ dont even have the right parts in standard ratings (not that I'd use them) and the plumbers supplier doesnt stock them either.
By the way, the cannon I have in mind is a piston exhaust valve cannon, 2 inch barrel, 4 inch chamber, 6 foot long barrel, 4 foot long chamber.