Re: T-Shirt cannon pnuematic set ups
 

Okay. I've been following this for a couple days. I figured that a t-shirt cannon would be a nice idea for our team, since at least half of us are graduating this year. This leads me to ask some questions before attempting a build.

Question 1: In regards to the air tanks, what kind of material could I use for pressurized air storage?

Question 2: Is it possible to use a high-pressure rated tank or such for a "rifle-style" t-shirt cannon without the need of having to carry around a storage tank?

Question 3: On the barrel part, since I DON't plan to use PVC for storage, can I use a strong duct tape-wrapped PVC pipe for just a place to load the t-shirts?

Question 4: What is the best way to design one that is safe? (We don't have a huge budget, so buying one is a bit of a problem.)

Question 5: What kind of sprinkler valve/solenoid should I use and where can I get one from?

Re: T-Shirt cannon pnuematic set ups
 

I don't know what thread it was in, but someone on this forum posted awhile back about doing some tests and finding that duct tape doesn't prevent shrapnel.

Re: T-Shirt cannon pnuematic set ups
 

Well, I've been tinkering, looking at Fusion's setups, and I've come up with my own design. Now, I wouldn't go replicating the idea I'm going to post if I were you, not until I give some feedback on how it did.

Here's the setup. I took a two foot long, 3-inch PVC pipe, added a 3in. coupler, put a 3-to-1 1/2 reducer, then a 1 1/2 to 1 reducer, to fit the Rainbird Sprinkler Valve. The Sprinkler Valve electrical system I'll explain later.
keep in mind that the PVC IS NOT USED FOR AIR STORAGE AT ANY POINT ON THE GUN! the only time it comes in contact with air is when the gun fires, and even then it's triple-reinforced in the joint sections, and I made sure to take an extra careful amount of time while assembling it.

Next, I plan to get hold of some tubing that can be pressurized to at least 110 PSI. This will enable me to have a variable adjustment rate without a risk of bursting. The hose will run to a connector, which will be tapped to an old Freon tank, much like Fusion's design. The tank will have a fill nipple, a pressure gauge for the tank, a hand valve for on/off, a regulator, another gauge for the regulator, and then the place to mount the hose.

As for electrical, I bought one of those little black boxes from Radio Shack, took a toggle switch (One of those that has a protective cover over the switch to prevent accidental turn ons). this switch acts as a safety. When this switch is on, a red light on the panel part is on, and a bright blue light powers up on the side. two of the 9v batteries are inside the box, and one 9v is outside of it attached by a "cradle". This allows me to pull the battery off for mainenance purposes, or simple power down. Next, the wires run to a "trigger" setup, and then to the solenoid wires itself, for activation of the valve.

Again, I wouldn't recommend attempting this until I have posted back with lots of feedback and testing results. If you do, okay, but I hope you take the time to think things through. I don't want to hear of someone getting hurt because of my design. Better me than you. Good luck, cannoneers.

Re: T-Shirt cannon pnuematic set ups
 

1> Use steel or aluminum tanks rated for 3x higher than your working pressure. Other materials may be used but stay away from PVC as it fails explosively.

2> You can use a smaller High pressure tank. The compressed air will weigh the same and the tank will weigh less. Again I suggest a 3x safety margin from storage pressure. Also, you will need to regulate down from this high pressure and that may cause restriction in the air flow.

3> Duct tape does virtually nothing if the PVC fails. DO NOT USE PVC. I cannot stress more that PVC does not like the shock loads that an air cannon provides and when it fails (not if) it will fail explosively.

4> Understand the forces used and the gas laws that apply (especially that gas exerts the same force in all directions ... not just out the barrel). Design with safety in mind and always err on the side of caution.

5> You need a valve with a large orifice that unseats quickly. Many have chosen sprinkler valves for this type of use ... but I'd look closer at vane valves myself.

Good luck and play safe.

Re: T-Shirt cannon pnuematic set ups
 

The PVC barrel will see a shock load that is equal to the pressure in the tanks. This shock load will be applied in under 1ms. It is this shock load that will sunder PVC as the PVC cannot expand fast enough when the shock load is applied (cannon is fired).

Again, I highly recommend not using PVC for ANY pneumatic device ... especially ones that will sustain shock loads such as air cannons.

Re: T-Shirt cannon pnuematic set ups
 

Okay. I wanted to clarify that, and it's a little easier to understand when you put in in terms of a shock load. I've got some other tubing for backup in case it wasn't going to work, with all the fittings ready. Thanks for clarifying that.

grateful, Sean :)

Re: T-Shirt cannon pnuematic set ups
 

team 1236 here and i have built one and it works great!


here goto this page on the site


http://www.chiefdelphi.com/forums/sh...ad.php?t=69073

Re: T-Shirt cannon pnuematic set ups
 

This is what we came up with.

Re: T-Shirt cannon pnuematic set ups
 

If in fact PVC is incredibly dangerous I have a few questions.

The discussion here has been only about air powered guns. Is there any greater or less danger in combustion guns? ( I'm aware that this would be disallowed on school grounds, its just a question of principle) I imagine that the lack of high pressure storage gives some what more safety though there is more of a spiking pressure affect that could counter act this.

Also on the topic of air cannons what are peoples opinions on the below link?

http://www.spudfiles.com/

I realize that it is the internet and not a well researched set of standards but one must question the danger involved if there has been a large community of people using these devices for years now. They have there share of accidents (as does any hobby such as dirt biking or snow boarding, etc) but it would seem that they only happen to people who didn't follow the well known safety practices and construction techniques established over time by the general spudding community. I guess that that if PVC were as dangerous as we are discussing then most of these people would have killed themselves by now.

Re: T-Shirt cannon pnuematic set ups
 

I would definately say thats a combustion gun would be even more dangerous:ahh:

PVC SHOULD NOT to be used EVER for anything being pressurised except for WATER and this should be the end of it(unfortunately it most likely wont:( )

and on the topic of alot of people using PVC, I belive there just asking for it, but its thier decision:o
Ill' give you that PVC dosent ALWAYS explode(which is why alot of people use it) but IF it does,someone COULD be seriously hurt, I dont know about you guys, but I would rather not risk having someone else injured because of me:rolleyes:

I also belive this has been said before MANY MANY times by far more experience people than me

Re: T-Shirt cannon pnuematic set ups
 

This is the most reoccurring issue with air launchers and combustion "guns". PVC is extremely dangerous!!
The PSI rating printed on the pipe is for liquids NOT compressed gases of any sort. The biggest problem with PVC is that its failure, when it occurs, is catastrophic. PVC shatters into numerous sharp shards that can be propelled at dangerous levels. PVC generally will not exhibit signs of fatigue until it explodes. People have also argued that PSI is PSI, so why isn't PVC safe with compressed gas? By the very natural of solids, liquids and gases, gases will release stored energy much faster than a liquid will, even liquids can still dangerous.

As far as your logic of a lot of people using these devices and none being hurt. That is a falsehood perpetuated by the internet. I have seen posting of failures but they are few and far between because most people don't want to post their failures, only their successes, and they certainly wouldn't post if someone was injured (don't you think the lawyers would love to get their hands on that incriminating evidence). Also, in most cases these people use these devices a few times before tiring of them, or getting caught (combustion guns). They've rolled the dice a few times and lucked out. PVC failure is generally from fatigue which means each time you load and unload the pipe you stress it and each time your chances of a failure increase. Load that pipe enough times and it will certainly fail.

I personally know at least four incidents of PVC failures. Luckily, no one was seriously hurt ONLY BECAUSE OF PURE LUCK! In one case, an individual had a charges air launcher under his coat. Luckily it failed away from his body, but it completely shredded a heavy winter jacket being worn. If you saw the jacket, you'd think the person wearing it was DEAD! Pure Luck plain and simple.

Our Dewbot T-shirt air launcher is built with an all metal storage accumulator, piping, and valve system in which every component used was rated at over 150 PSI. Where we used flexible hose (after the solenoid valve) it was rated at over 180 PSI and is reinforced so that a rupture would only cause a tear in the material. The launcher tubes are made out of polycarbonate pipe which is rated at 9000 PSI and was $11/foot. That should give you some idea of how seriously we took safety when using plastic pipe, even polycarbonate.

Don't be misled by what you don't find on the internet.

Re: T-Shirt cannon pnuematic set ups
 

It terrifies me when people make posts like this without understanding they may very well be placing somebody in harms way.

I wonder what type of professional engineering or material engineering degree this person has. I wonder what license and what expertise are this person bases his statement on.

OSHA and the manufacturers say NO.

http://www.osha.gov/dts/hib/hib_data/hib19880520.html

Re: T-Shirt cannon pnuematic set ups
 

No offense, but I could ask you the very same question. I don't think you've explained what degree you hold.

Re: T-Shirt cannon pnuematic set ups
 

Combustion guns use expanding gasses to propel the object, and therefore are still inherently dangerous to use PVC with. In addition, the lack of specific gas pressure control and the addition of heat will most likely cause the PVC to fatigue faster.

People will always do stupid things and then brag about their "success". Don't be the one that "fails".

Please take it from someone who has had a 1 liter volume, pressurized to 100 PSI, blow up on him at close range (ME). It is dangerous, very dangerous.

Re: T-Shirt cannon pnuematic set ups
 

First of all I have read the entire thread and am well aware of the facts you stated in red text several times before. I wasn't speaking so much as in defense as more of an awarness of a very large community. It was an attempt to bring to light more than what had been discussed already. The internet is and can be very misleading but none the less it is present and full of more empirical data (probably positively biased) and trial and error on the subject than can be completely ignored.

On a side note I have built and operated a combustion gun for several years now. (if you can't make one you probably shouldn't have one::ouch:: ) Its stored inside away from temperature extremes, I do not fire it in extreme cold, I use weak fuel such as hairspray and I always treat it as an actual fire arm. That is why I was probing into combustion guns.