Coaxial Piston cannon [VIDEO]

[Joelduf]

UPDATE
I will be using a pulley system to charge and fire the cannon from now on due to the fact that i am using DWV Tees and elbows, so there is no reason to fear me blowing my face off, or anything else related to the consequences of exploding PVC cannons. When or If the cannon explodes, I will rebuild it with pressure rated parts.

So, about a week ago, i decided to build a cannon that would shoot ice/sand/ etc... filled soda cans, and set myself a limit of 65$ to spend. I have built a cannon before, but it was a very simple combustion that made a whole lot of noise, which eventually caught the attention of my neighbors, who had just bought a very noise sensitive dog. I had the cannon for about a year before this, and used it pretty infrequently without issues. They complained, and i decommissioned it.

So, i went to the home depot and got parts, including:
A 10' section of 4" pipe
4 inch to 3 inch coupler
A Tee, 4"
An elbow 4"
4" end cap
3" end cap
Pvc cement and primer
A cleanout, 4"

I already had:
A 6 foot section of 3" pipe
Bolts/nuts/washers
Rubber sheeting
Valves
Compressor, Hose etc...( obviously)
Pressure guages

Next, I glued the thing together on Saturday night, with a whole lot of pleasant fumes to accompany me. The next day, i fumbled around with the goshdarned piston valve, and dealt with frequent premature firings and the such, until I finally solved the problem on Sunday night after like eight hours in the garage.

Today, I fired the Cannon.
Sweet Jesus.
I fired a can full of water ( I didn't put the cans in the freezer long enough for them to freeze, and it was starting to rain) with duct tape on top and some newspaper for wadding. I pressurized the cannon to 70 psi, and turned the valve with a long stick to be safe. Needless to say, i pretty much had an orgasm upon firing it. I'm guessing the can crushed before it even left the barrel due to how it left a trail of mist in its wake, but regardless, the thing had to be going at least 70mph, at just 70 psi. Unfortunately, it did not occur to me to take a video, and it is now raining, but i will probably post a video tomorrow.

Pictures of the cannon:

http://img257.imageshack.us/img257/9022/dsc1486.jpg
http://img257.imageshack.us/img257/9022/dsc1486.jpg
http://img130.imageshack.us/img130/4108/dsc1488.jpg
http://img205.imageshack.us/img205/1223/dsc1489w.jpg
http://img257.imageshack.us/img257/417/dsc1490a.jpg
http://img252.imageshack.us/img252/703/dsc1491.jpg
http://img130.imageshack.us/img130/2634/dsc1492g.jpg
http://img101.imageshack.us/img101/7383/dsc1493n.jpg
http://img205.imageshack.us/img205/9979/dsc1494.jpg
http://img101.imageshack.us/img101/7584/dsc1495.jpg
http://img527.imageshack.us/img527/3125/dsc1496.jpg
http://img252.imageshack.us/img252/5508/dsc1497s.jpg
http://img257.imageshack.us/img257/7026/dsc1498.jpg
The barrel is off center because the launch blew my nuts right out of place, so i guess I'm gluing those in later.
[youtube][/youtube]
40psi test shot

More news: I have fiber-glassed the DWV thickly which no doubt has strengthened it. Also, this will prevent the cannon from shattering, instead producing a tearing action. Finally, i have set my limit at 70psi, which is very much satisfying enough for my tastes, seeing as it can launch QUITE heavy projectiles even at 20psi with great speed.
Problem Solved.

Example: It shot a baseball through 2 sheets of 1" particle board at 20psi.


Video: A fail test at 30psi. I don't even have much of an idea what went wrong. Maybe It leaked down to a low pressure.
[youtube][/youtube]

[Techie]

The barrel is off center because the launch blew my nuts right out of place, so i guess I'm gluing those in later.

ROFLZOR


Pretty gun, might i suggest a black and neon green paint job? Also, why don't you vent through the small ball valve?
cant wait to see the video

[Joelduf]

Also, why don't you vent through the small ball valve?

It doesn't vent fast enough.

[jmadden91]

Those pictures are freaking huge!!

I hate to be the one to tell you this mate, but that is full of DWV

[Joelduf]

Sorry about the picture size(3872x2592), I took it with a Nikon d40x, which happens to be my second most favorite thing right now . Also, i am aware of the DWV, but it was all that was at the home depot. It hasn't exploded yet!
:/

Do you think it's possible to somehow swap out the non-pressure rated joints for pressure rated ones at all?

You know what, I will just stay inside my shed when i fire it and rig up a remote firing system to be safe. Well, It'll be more tedious to fire than before, but at least i will be safe.

[absinthe]

you can carefuly cut a slot in the DWV and then with a heat gun or hair drier heat up the glue and then peel the DWV away.. make sure you clean all the old glue off before you use the new fittings

[Technician1002]

Are you using some kind of bumper? Without one, the expected life of the launcher is less than 100 shots.

[Joelduf]

Of course, such a venture would be quite foolhardy with a cannon such as mine.

I will be using a bumper (the piece of thick foam), specifically the one in the pictures, unless it doesn't seem like enough. It IS pretty dense stuff.

[jackssmirkingrevenge]

The barrel is off center because the launch blew my nuts right out of place, so i guess I'm gluing those in later.

ROFLZOR

Precisely my reaction

I must admit I was more taken by the humorously written report than the actual launcher hehe

[Technician1002]

The barrel is off center because the launch blew my nuts right out of place, so i guess I'm gluing those in later.

ROFLZOR

Precisely my reaction

I must admit I was more taken by the humorously written report than the actual launcher hehe

If the barrel spacing was done on the other side of the T, then they would have been out of the high speed flow path. Speaking of the flow path, is the barrel in the way of the flow from the chamber? A slightly longer piston and shorter barrel extension through the T could improve the COEF tremendously.

How far does the valve seat extend into the T? It looks like it extends all the way in and then out the other side so it is blocking a good portion of the flow from the chamber.

With the valve further forward in the T the pilot can be made much smaller.

[Joelduf]

Yeah, it goes about an inch beyond the T. All The air seems to escape VERY quickly upon firing, though. Getting the spacers in beyond the T is very much out of the question, so forget it. Good idea though. Maybe I'll do it whe the T blows off the cannon.

[MrCrowley]

You have a cleanout cap on there...damn dude, is there a hot nurse at the local hospital or something?

It's a shame about the DWV, I wouldn't feel safe with it at all. I don't even feel safe with pressure rated PVC these days.

Do you mind if you just hot link a most of the images and only leave a few embedded, it took for ever to load the page and I have a decent internet connection.

[psycix]

One day, your piston will come out of the cap saying "PEEKABOO!"

Another thing is the pressure gauge installed on the chamber. Next time, drill the hole through a fitting+pipe so that you've got a double layer of PVC.

For the rest, it seems a decent cannon. Try to build another one, but then with safer parts.

You have a cleanout cap on there...damn dude, is there a hot nurse at the local hospital or something?

That's worth a signature!

[Brian the brain]

because the launch blew my nuts right out of place

This is too funny!

PEEKABOO!"

That would be..

PEE-KABOOM!!!

[Joelduf]

At this point I don't even care if it explodes, because i am going to be behind a thick wall with a remote trigger and pressurizing system. I will just rebuild it with pressure rated parts if it does explode. I just want to get the most out of the components i have now so I know i didn't waste TOO much money.