T-shirt Launcher
 

Hey guys so basically this is the year our team wants to go from meh to great. Our first objective was naturally sponors. We had 0 sponsors in the beginning of the season and now we have 4. The unforunate thing is we have money now but we need mentors and sponsors with machining facilities ad stuff of that nature.

So to attract those kind of sponsors we need to make something cool and something that can be used for event. We are also sponsored by cablevision now which owns madison square garden. Sooooo naturally t-shirt cannon is the idea that comes to mind.

we have a drive train from I think 2010 that we are going to outfit with the new control system or just redo the wiring. Its just a standard kop chassi which is fine. The issue is the cannon itself.

I saw a thread a while back with someone saying they would give a parts list. we have a bit of phenumatic experience and have supplies its just the speciallty stuff and how it works.

It also cant completely break the bank. We have some money (1,100) and we were going to spend it all on supplies but we can get away with 750 in supplies leaving $350 for parts for the t-shirt cannon.

thanks - Sam

Re: T-shirt Launcher
 

You can make a really cheap and easy setup using a sprinkler valve. That's what we've been doing since we first built a t-shirt cannon. Basically you would store compressed air in a tank and then run a house to a sprinkler valve which would be attached to the back end of the barrel. The valve is triggered electrically.

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Whatever you end up building, please only use parts rated for AIR pressure. This means no PVC pipe or lawn sprinkler valves.

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have you had any issues with it breaking as I see mixed reviews already. Also ive hear pvc could be dangerous so what do you recommend as the barrel.

Would the setup be Compressor, storage tank (probally something cheap and dirty from harbor freight, and then to the sprinkler valve.

Or would it be pump large storage tank solenoid to regular storage tank..

Sorry for being such a noob just want to make sure I know what to do myself before I design and lead the build.

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We built a t-shirt cannon last season to get practice for build season

https://www.youtube.com/watch?v=btgNmKMj8qg

We used a harbor freight 5 gallon air tank, made accumulator tanks out of abs pipe, used sprinkler valves, and reused electronics from old seasons.

If you have questions, feel free to ask

May be asking a lot of questions if we fully go through with it. How much did it cost. We would probably do something lower end. I'm thinking no tilt adjust and only one cannon. It's funny that was the second time I watched the video haha I watched it first for inspiration.

Also what are the special parts you actually had to go out an buy like stuff most people don't have laying around.

Thanks

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We've never had issues with the barrel, valve, or hose through 5 years of use.

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+1. A pneumatic explosion is not something you want to have to deal with. At the worst, somebody could be injured or killed, and at the least, your program could face very serious review or be shut down. This stuff is too serious to be decided by whether sprinkler valves and PVC are cheaper than legitimate pneumatic components.

I would recommend copper or brass piping for any pneumatic operations dealing with such large volumes of air due to the fact that it is actually rated for air pressure and less likely to shatter if it does fail.

I feel you for sure but I just want to make sure we aren't going to triple. Our spending to buy into a myth

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The one we built was in the neighborhood of $5000 just for parts. But we started from scratch. The custom sheet metal chassis, paint job, and specialty designed adapter block to go from the solenoid to the barrel was donated, everything else we bought.

We are using twin scuba tanks. The pneumatic system was designed by a colleague who is a PE in piping design. We have several safety rated devices (Burst discs) in the lines so that we don't over pressurize the system.

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It isn't a myth though. PVC isn't rated for air pressure and when it fails it does so spectacularly. It will work fine for a while, you just won't know when that while will end. And when that time comes, the result will at the least let blood come out of someone. The worst case scenario is much, much worse.

We shoot about 100 feet with something like 20psi. Pvc will not burst at 20psi. Look into 12v air horn solenoids instead of sprinkler valve both work well

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There's always a hot dog shooter. Definitely not PVC level, as Philly Phanatic can get them into the upper seats and needs a license to shoot. Story and video here.

Now I want a hot dog!

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Please, Please, Please do NOT use PVC for any pneumatics, including the barrel. It's failure mode is catastrophic.

We're building a t-shirt cannon as well and we are using a copper tube for our barrel.

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PVC is NOT rated , nor designed for air pressure. It doesn't matter what pressure it is at, pressurized gas in PVC is dangerous. This warning is from Charlotte's Pipe safety manual.

Please be safe, use proper materials.

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Unfortunately, if you can't afford to do it with the proper materials, it's probably not worth the possibility of serious injury in the end.

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In order to get much range at low pressure, you'll need to have large pipes and valves. On our air cannon, we use a 3/4" solenoid as the smallest point in the line. This means that we cannot use a tank designed for tools; the flow is not enough. We have a large (probably 8 gal) cast iron accumulator with about a 2" fitting at one end. We usually charge to about 40-50 psi, and have thrown t-shirts over the top of our press box with it at 60. Also, a large-bore relatively short barrel gets more of the energy to the shirt than long and narrow. We're currently using a 3" barrel about 20" long. The 3" barrel also works well with small foam rubber footballs.

We figured out a very simple way to prepare the shirts for the launcher that does not require any tie wraps or string or tape:

1. Lay the shirt flat on a horizontal surface
2. Lift the bottom hem a few inches, and raise (relative to the shirt orientation) until the fold is at the armpit.
3. Lower the hem until the next fold is at the shoulder
4. Repeat the two previous steps until you're out of shirt
5. Fold one sleeve over the shirt body
6. Roll from that sleeve, across to the other shoulder
7. flip the other sleeve inside out and wrap around the cylinder, like folding socks.

This fits a large short-sleeve shirt in our 3" barrel nicely. A small shirt may require making the cylinder a little shorter, and an XL a little longer.

Ok so what do you recommend in particular.

I've heard copper pipe is ok but what about conduit. That stuff is still decently cheap.

Also how thick and how much do we need.

Lastly what do you reccomend as a valve is a sprinkler valve ok.

Well we can't afford 5k that's for sure. We also don't need or want anything fancy looking we just want to shoot one shirt decently safely and move around

Re: T-shirt Launcher
 

Copper pipe is good.
Conduit may or may not be good. If it is plastic (especially PVC), do not use it. If it's metal conduit, that should work.

Copper 1/16" wall is enough for the ~60PSI shock that the barrel should see max.

The biggest thing with the valve is safety and leakage. Make sure the valve is GAS rated for the max pressure it will see. The gas rating is important because most other valves will leak as well as possibly burst.

The most important thing here is safety. Remember that this will be in the public eye. Any failure, especially one that results in unexpected release of pressurized air, is very bad.

If you cannot afford to ensure it is completely safe at all times then don't build it. That being said, with some leftover KOP/FirstChoice parts you should be able to build a decent safe single shooter for a few hundred dollars.

What valve do you recommend.

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Something like This would probably work. It's designed for use with Air and is safety rated to 72PSI.

It's flow may be too restricted though ... I haven't done the calculations.

It also has BSP threads so connecting to it is ... fun.

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so we would need to buy
1.that solenoid
2.harbor freight 5 gallon air tank
3.3 or 2 inch wide metal conduit

and we would also need to use(that we have)
1.compressor
2.normal tubing
3.chassis

and some fittings.

is there any weird adaptors or entire components im missing.

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You'd want a dump (ball) valve, an overpressure (Poppit) valve, and a pressure switch to shut off your compressor at a safe pressure.

Other than that, it looks like you have a good list.

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We're using one that looks just like this (I think it's the same one). We're switching it with a relay module, though a spike would also work. We have two barrels, and one of these on each. We often fire them about a tenth of a second offset from each other; 50ms for each to be open is more than enough.

We currently have all steel, brass, and rubber up to the final nozzle, and PVC barrels. Based on what I've read here, we'll be making some mods before next football season.

BTW, we did not use a 'RIO for our air cannon - an arduino on the robot with an xBee comms module, and a remote with just an xBee module and a 9V battery and some buttons/joysticks to dive, shoot, and someday aim in azimuth. Our accumulator is filled manually from a scuba tank; the accumulator holds enough for about 40 good shots before losing pressure.

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We had the same discussion a few years back and opted to go a different route. We made a giant nerf gun which shoots 1' sections of pool noodles. At top speed it will now shoot a "nerf bullet" about 70' which can then be traded in for a t-shirt or whatever you choose. It also allows for good demonstrations with younger kids and has little chance of injury. The pneumatics only feed each noodle into the spinning wheels which work like a baseball pitching machine.
here is a picture location

http://www.chiefdelphi.com/forums/sh...099#post776099

Re: T-shirt Launcher
 

I share everyone's rightful concern for safety, and I certainly lack credentials on PVC and air pressure vs. water pressure. At the same time, I have to question whether PVC knows what's inside it (water or air). Pressure, it seems, is pressure.

The documented examples I have seen of PVC failure have occurred at low temperatures, where I will agree, PVC gets brittle and dangerous. If inside a warm building at 1/2 rated pressure, I would tend toward not worrying excessively.

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We'd never get permission to put our tires on the gym floor. The main place we use our air cannon is outdoors during football season. Even in the deep south, I'm getting a bit queasy.

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You are incorrect that pressure is pressure. Liquid (which PVC is rated for) is incompressible where gasses (That PVC is not rated for) are compressible.

The issue with PVC is the failure mode. When PVC fails with liquid in it the internal pressure relieved immediately (due to liquid being incompressible) thus there is little time to accelerate the shards that are generated during a failure. Gasses, though, relieve pressure only as fast as the gas can escape, thus giving the force plenty of time to accelerate the PVC shards.

Hope this helps to explain the difference.

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Have you had any issues with the pvc barrel. We are in ny which is cold. We would probally use ours most at football and lacrosse games which are both cold.

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No, but we've only used the current barrels at three games, perhaps 100 cycles per barrel including testing. I'm not going to wait to have a problem to fix an unsafe condition. ::safety::

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PVC also deteriorates with exposure to UV radiation. This may not be a problem immediately, but years down the road this will become a concern.
The cement used to bond PVC is also not rated for air pressure.

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We've built a t-shirt cannon, and I'm going to be really unpopular here and mention something that the non-PVC'ers haven't said.

PVC is rated for high enough pressure--it just isn't rated for air pressure. The reason is because of water-hammer--go figure--that it's fine to use PVC with water and not with air.

"Water hammer" if you didn't know, is a pressure spike that occurs when you close a valve quickly on moving flow, which can cause instantaneous spikes of pressure as high as 400psi or more. Water hammer--with air--is what explodes PVC pipes. I used to design railroad pneumatics, so yes, I've exploded PVC pipes before. It's loud and dangerous and I don't like loud and dangerous. Please forgive me, we've most all done stupid stuff before.

But think about this...If I use a sprinkler valve that's plumbed with steel NPT fittings--I have all metal in the 'firing' section of the system.

I only need to use PVC for the barrels. The barrels CAN NEVER see a spike caused by water hammer, because you cannot shut off the air you've put in them. If the barrels were to fail--even catastrophically, the worst thing that could happen is that it shoots a t-shirt. One end of the barrel is open to the world. Even if they developed a huge crack in them, the air would still exit the open end with the t-shirt.

People have been making potato guns and t-shirt cannons with PVC barrels for many years. Do you know how much a three-inch ID piece of steel or copper costs? Or how much it weighs? Just to be safe, we never run more than 60 psi, but our 'gun' is four years old and still not broken. Also, the design of a sprinkler valve--which is piloted--prevents it from being closed quickly. Another built-in protection from spikes.

We built a working 2-PVC-barrel t-shirt cannon and the shooting parts of it cost less than $50.

The air-bubble, the Thomas compressor and the kit-frame all came from 'inventory' in the shop.

I think all of the no-PVC'ers here are going to prevent many teams from building t-shirt guns.

Re: T-shirt Launcher
 

The 'gray' PVC is 'UV stabilized', but don't forget that simply painting PVC protects it from most UV.

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I agree with you that using PVC for the barrel is fine because the barrel is not storing pressure. I am more concerned about people using PVC as the pressure storage tank.

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Water hammer produces such high pressures because the water is incompressible and massive, so stopping it suddenly requires a large, quickly applied force - hence a hammer. Air is light and compressible. In fact, small vials of air are used as water hammer suppressors. Bottom line is, that I don't think that the problem with air in PVC is really water hammer.

I'm still planning to replace those PVC barrels.

Re: T-shirt Launcher
 

This is not correct.

Water hammer spikes pressure as high as it does because it is not compressible. And while Air hammer will occur, the pressure spike is much smaller.

The issue, again, with PVC and gasses is the FAILURE MODE. A barrel will see at least enough pressure to move the ammunition, if not significantly more pressure. Should the barrel fail, it will fail catastrophically and explosively. Please, DO NOT USE PVC for ANY gas pressure.

and just because some people have made potato guns out of PVC and pressurized air, does not make it right or safe. Remember, these t-shirt cannons are, by their very nature, designed to be in front of the public where a catastrophic failure could cause injury to people near by. Think of this before you design your cannon.

I have no idea who's right but you did put some science in which validates your opinion a bit. I'm a starting to wonder if this "no pvc under air pressure" Is like "always wear an anti static strap while building pcs". I don't know who to trust but I'm going to look and try to find some metal pipe big enough. If I can't find a free pipe pvc it is. There will be testing and the pvc barrel will be a wooden box so if it did break it would be contained?

I've played with pvc making gymnastics equipment and have seen it break under stress. But I can't find any videos of someone getting injured from pvc bursting at 60psi

Re: T-shirt Launcher
 

Placing the PVC in a wooden box will do nothing to contain an explosion, it will just create more shrapnel. Do not use PVC as an air tank. Only use air pressure rated tanks and fittings. And as Daniel sad above, the "water hammer" explanation is questionable. Every PVC pipe manufacturer, and several regulatory agencies do not recommend or prohibit using PVC for pressurized gas. See warnings W-3, W-4, and W-5 in this document. W-5 specifically warns against compressed air guns:

Compressed air is dangerous. Even at relatively low pressures, there is a lot of energy involved. If you use PVC for compressed air situations, you are putting yourself, and everyone around it at risk. If you can't afford proper materials now, wait until you can.

Re: T-shirt Launcher
 

What did 254 use for their barrels and fittings?

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Aluminum barrels, and pressure rated tubing and fittings.
http://team254.com/category/frc/shockwave-build/

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254 used aluminum barrels.

Edit: Ninja'd.

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well..... we cant afford anything 254 does

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Your team is located in the same town as Northrop Grumman, I think. Have you ever worked with them as a sponsor? Perhaps they could fund this project, or provide you with materials. They certainly have aluminum tube stock sitting around that they could donate.

Re: T-shirt Launcher
 

As for valves, we used this: Asco 8353C035. It is a high flow air valve designed for back pulsing filters.

As to the PCV. Pressure is pressure. But PVC (the kind they use in for pipe) is brittle. When liquids decompress, they don't expand like gases do, so liquids don't throw shrapnel the same way air does when the pipe shatters. The density of air is so small & the distances involved are small so you do not get significant pressure spikes from "water hammer"

The PVC is not going to randomly burst under normal conditions, with air or water. But if it does, maybe it gets bumped in the wrong way, something hits it, etc, it has a bad failure mode. Well documented. Big legal liability. Especially for any mentors on the team that are registered professional engineers. Makes the cost for other material seem small.

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well.... thats complicated. we have tried to get in contact with them on numerous occasions. I mean this town was practically built on them. Its across the street from my house and sits there dead. Basically the company wants to get rid of the branch in long island and has wanted to for a long time. I know Mr.McLeod from team 358 was one of their previous employees. Basically all that gets done there now is movies. They went from 10s of thousands of employees to hundreds. This thread alone has some valuable knowledge about what they used to do http://www.chiefdelphi.com/forums/sh...t=29295&page=2 but from my understanding they no longer support first much. I could be wrong but they havent ever replied to our phone calls or emails and even though the place is across the street there isnt exactly a front entrance. I know they support the PoBots another local team the town over but I assume they had a parent or faculty member who knew someone to get them in contact with the company. Its a shame because its our towns legacy but we would be without our biggest sponsor (cablevision) if they didnt sell some land to them a while back so I guess its not all bad.

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I see the liability. Thankfully or should I say unthankfully none of our mentors are enginners. Our lead mentor teaches tech our second lead is a programming and math teacher and our third mentor is the orchestra teacher. But... yea I see what your are saying our bot exploding in the middle of a crowded place isnt good for anyone and is especially bad if its at a real arena like madison square garden (im pretty sure we cant afford to fix that) I see the point and my final decision is no to pvc. However I will be on the lookout for tubing.

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http://www.northropgrumman.com/Corpo...uidelines.aspx

I just did a lot of surfing and found this...going to bookmark it and figure out what to do.

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Great idea! Good find.

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Okay, I have quite a few people disagreeing with me saying that the failure mode for PVC isn't water hammer, but no one presenting evidence. If you simply read the wikipedia entry on water hammer, you'll see that is it common with air too. With water it isn't explosive as it is with air because water isn't compressible. Even the engineers studying this airplane crash attributed it to water hammer.

And it is true that in a water-system you can introduce compressible trapped-air to prevent water hammer because you've introduced a 'spring' and suddenly you have a second-order differential equation-- that system won't be able to find 'reflection' to 'hammer' the end into a pressure spike.

And I've seen some other people saying that the barrel will "fail catastrophically" but it's not clear to me how even that can result in shrapnel from the back end of the PVC when the barrel-end of the system is OPEN. And again, I point out, I've done this and I've seen PVC fail using it for air pressure on a test system for train brakes. I didn't shrapnel, it just blew at a joint. I still maintain that the barrel won't introduce shrapnel, even in a catastrophic failure. It will blow a joint or split.

Also, when I blew up that accumulator tank that I was using, it was while quickly opening then CLOSING 1-inch dia piloted valves. I maintain you have to close a valve to get water hammer and with these systems, you never close a valve under high flow.

If I'm wrong...and I sometimes am...provide me with a logical explanation of why and how PVC--rated to usually 100+psi for water--fails with air.

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Also, if you don't want liability, don't build a t-shirt launcher. The purpose of this machine is to aim projectiles at the crowd.

Projectiles are dangerous and litigious.

Wow this has become a pretty big debate can't wait to see some evidence from both sides.

Ive seen pvc crack under pressure (tried to make long paralletes out of pvc and when I did handstand on it it cracked) thd crack was super clean and smooth.

But putting flex on it and air pressure through it are different. I kinda want to see a video of someone's pvc cannon exploding or an experience of that. If there's nothing I'll still try not to use pvc but won't go crazy if we need to.

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http://youtu.be/IVO4_hUvFsc?t=1m8s

Keep in mind that the forces involved in this video are far less than those that can be produced by the typical FRC robot.

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well of course it eventually exploded. It has a closed front. Our launcher barrel would obviously be open.

Also dropping a weight over and over again from 12 feet would damage anything.

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Please read This paying attention to the failure modes and summary.

here is another website stating not to use PVC with pressurized gasses.

and here's OSHA telling you not to do it.

Oh, and BTW,your cannon barrel is NOT open as you have a t-shirt inside that is acting as the restricting orifice that allows the pressure to build up behind it ... which is why the t-shirt flies out.

One last thing. I happen to be someone who has had a 1 liter volume, made of PVC, with 100 PSI inside of it blow up less than 2 feet from me. There was no warning of the impending explosion. The only reason I am here to talk about it is that it happened to blow out the opposite direction. I am one who knows what the failure mode is like (back then I didn't, and I'm lucky my ignorance wasn't fatal). So when I say don't use PVC for pressurized gasses I know what I'm talking about.

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The pyrotechnics industry also highly discourages using PVC pipe. When PVC fails, it shatters and creates splintered shrapnel which can seriously injur or kill someone. They use EPDM pipe or fiberglass for mortar tubes from 1.75" up to 12" diameter (for the big 4th of July shows). EPDM pipe is more expensive and a little harder to find that PVC pipe, but fails in a more ductile (vs. brittle) manner.

http://www.pyrouniverse.com/FAQ.htm#9 (this has some good examples of failed PVC pipe)

This is for information only. I don't encourage anyone to build a t-shirt canon with any plastic.

+1

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This is a little off to the side of the main conversation, but here is the T-shirt launcher we made last summer. It uses a balloon tank with a sprinkler valve and 2 Viair compressors. It has a water separator to keep moisture out of the tank (our last one rusted through the bottom). It also has a analog pressure sensor so I can set the pressure shutoff psi.

It runs off a cRIO-II. We will be putting addressable LEDs on soon.

http://youtu.be/H_IjhJFgQIY

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First of all any rigorous discussion on fluid dynamics that mentions water hammer and air in the same sentence gets points off. But this is CD and not rigorous. :0
Taking the second reference first. The "water hammer" reference was discounted by the NSTB. The accepted conclusion was aluminum has a fatigue life & the plane exceeded it by the high number of take off & landings relative to the relatively short flight miles of the air frame. See the Dehavilland Comet failures for another classic example of the fatigue of aluminum and stress risers which BTW effectively handed the commercial airplane market to the United States.

First example second. You should really read the article. Water hammer requires a quick closing valve on the exit of the fluid column. The pressure spike comes from the rapid deceleration of the fluid column. The spike is increased by the weight (directly related to the density) & the velocity of the column. It is decreased by the compressibility of the elements involved. So when you shoot a tee shirt, you might see actually see a vacuum in the barrel when the tee shirt exits the tube. Hard to predict what happens upstream of the valve without the specifics. I expect we see a vacuum spike in the accumulator of our cannon. it is a relatively small volume & we precharge it to 20-120 psi & fully discharge it on each shot. The cannon will constantly shoot a 70 yard field goal.

The reason why you get a large number of "PVC" works for me is that the pressure involved is well within the working pressure of PVC pipe. Failure is not a regular occurrence. The issue comes from the severity of the failure mode & the documentation from both the pipe manufacture & OSHA saying don't do it.

Really simple design and all we would have to buy is the barrel sprinkle valve and a water seperator(we are pretty close to the ocean and humidity is an issue) what barrel and tubing is that BTW.

We have 2 balloon time tanks that are filled but we can probably dump it all by making balloons for little kids.

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The tubing is just high density pvc hose. It's tied off at each end with hose clamps.

The barrel is just some 1/4" thick strong plastic type stuff. I don't know exactly what it is, but we have used the same barrel and hose for the last 10 years.

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I thought of something else to consider about a PVC barrels and air hammer. On several occasions we have tried to stuff too large a load into our pipe (particularly 3" footballs in our previous 2-1/2" pipe), and it did not pop out of the end; it some cases it barely rose at all. In this case, the load itself could be the cause of air hammer as it stops the air rushing up from the valve. I believe a rupture of the pipe would be most likely to occur at the supply fitting where the air speed is greatest. Here, the pressure would not be relieved by the load moving clear; all of it would be used in creating moving pieces of PVC.