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School T-shirt Cannon

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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School T-shirt Cannon

Unread postAuthor: rcman50166 » Mon Sep 14, 2009 12:57 pm

Hey, so I've convinced my school to let me build a pneumatic t-shirt cannon for our homecoming football game. I've decided to go with a co-axial piston valve cannon. This one will be of epic proportion. It will have a 36" by 6" chamber and a 28.5" by 2" barrel. The pressure of the cannon (for safety reasons :roll: ) will be 100 psi at most. The help I need is with the piston. I'm not sure what to use to cover a 2" bore and still be nice and light. For that I was thinking of using pine wood for the body of the piston. I also need help deciding the material to use for the seal. I was thinking of silicon caulk. Any ideas or comments? I have a budget of $400 for the entire gun.

Also I was wondering where I can still buy a Kobalt CO2 regulator. They don't seem to be available at Lowes anymore.
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T-shirt Cannon2.jpg
This is the design.
javelin.jpg
This is what the design is after.
GGDT tshirt cannon.jpg
The GGDT estimate. It gives me a range of around 300 ft. It seems appropriate seeing as it will be shot at a football game.
Last edited by rcman50166 on Mon Sep 14, 2009 2:06 pm, edited 1 time in total.
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Unread postAuthor: theBOOM » Mon Sep 14, 2009 1:05 pm

Sounds intresting... I'd look into technichan's QDV tshirt cannons they seem to work really well... I forgot the link to his video of one.. I'll look for it and edit if I find it.
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Unread postAuthor: rcman50166 » Mon Sep 14, 2009 1:07 pm

lol I'm sorry I haven't been posting lately, can you link me to the page?
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Unread postAuthor: cannon monkey » Mon Sep 14, 2009 1:23 pm

i have a 2 inch and it kind of hard to fit a whole tee shirt into it... might wanna check that a shirt fits the pipe
maybe it just my shirt but i couldnt get it in
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Unread postAuthor: rcman50166 » Mon Sep 14, 2009 1:32 pm

I have folded many shirts in many different ways. It seems that the diameter comes out to be 2.5 inches when its rolled in my hands. That is loose too. So it would be nice and tight at 2 in
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Unread postAuthor: cannon monkey » Mon Sep 14, 2009 1:36 pm

i tryed my best couldnt get it to fit lol but good luck
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Unread postAuthor: Technician1002 » Mon Sep 14, 2009 7:14 pm

I mentored a team launching shirts as mentioned by other members. Flat out, the current design won't reach 200 feet. Long skinny sausage t shirts turn sideways and very rapidly lose momentum.

Our contest was limited to a maximum of 100 PSI. The contest had a $400 budget. This sounds like dejavu all over again. Please tell me more about the official contest rules.

Our contest wiki is here.
http://inteltrailblazerschallenge.wikispaces.com/
Most of the discussion is pretty dead as during the build each team kept a tight reign on the designs, but after the entries were submitted for judging, the links on the left contain most of the information.

To help you study without re posting everything again in detail here, my youtube page has many videos related to the theory and construction. The design created a stir at work. The full size prototype wasn't much of a backpack item for show and tell, so I built a scale model that I use to demonstrate the cannon. Even the model provides plenty of range. With a tennis ball / shirt barrel attached it tosses shirts 200 feet which is plenty to reach into the stands at most school football stadiums.
http://www.youtube.com/user/Technician1002 I have the same username on youtube.

The model build is posted in detail on crazybuilders.
http://www.crazybuilders.com/forum/showthread.php?t=27


Good luck and after reviewing the material, post any questions.
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stadium1.jpg
The 200 foot range of the model at 200 PSI gives us this range at this stadium. Operating pressure is 80 PSI. This overlay is for range prediction for the Cure JM benifit concert Aug 8th. We took the model instead of the full size cannon. It uses much less air.
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Unread postAuthor: rcman50166 » Mon Sep 14, 2009 8:05 pm

Well to begin with it is not a contest so there are no rules. We are limited to 100psi for safety reasons. I just essentially brought up the topic at an ASME meeting and they gave me the go-ahead and funding to build it. The design is actually based off of a design I made a few years ago. So I wanted to use it because I wanted it to be made without using my money. (or what's left of it.) We want to keep it pnuematic so it doesn't singe shirts. It needs to be able to shoot at least 5 shots in a row without getting it recharged at a remote location and needs to be portable.
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Unread postAuthor: JDP12 » Mon Sep 14, 2009 8:13 pm

I'm buildin one for mine too- I'm doin a 4" barrel sealer... A little overkill but who cares
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Unread postAuthor: spudtyrrant » Mon Sep 14, 2009 8:20 pm

i would go 4" chamber it would be smaller, lighter, and perform just as well or make the barrel longer, that chamber is major overkill. Instead of using 100psi you could increase the barrel length use 50psi and get the same performance :)
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Unread postAuthor: Technician1002 » Mon Sep 14, 2009 8:31 pm

spudtyrrant wrote:i would go 4" chamber it would be smaller, lighter, and perform just as well or make the barrel longer, that chamber is major overkill. Instead of using 100psi you could increase the barrel length use 50psi and get the same performance :)


:D I get 200 foot range instead of 350 with the large one.
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Tennis ball barrel1.jpg
TB or T shirt barrel
Tennis ball barrel1.jpg (36.58 KiB) Viewed 1475 times
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Unread postAuthor: rcman50166 » Mon Sep 14, 2009 9:01 pm

Well I'm considering it but the price of the gun is getting quite high. I need some help designing a cheap piston. The one I have designed costs like $50
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Unread postAuthor: Technician1002 » Mon Sep 14, 2009 9:32 pm

rcman50166 wrote:Well I'm considering it but the price of the gun is getting quite high. I need some help designing a cheap piston. The one I have designed costs like $50


What are your fabrication abilitys and tools? If you have to pay someone to build it for you the cost climbs quickly. If you have access to shop tools the cost can be very little. My valve body cost way more for the length of 2 inch pipe than the valve piston by a long shot, unless you count the purchase of a drill press toward the cost of my piston.

I looked at your design. 2 inch is too small for the barrel. The overall design is pretty much a copy of this one.
http://didacticwhoosh.com/
http://didacticwhoosh.com/design.html Design page
You may wish to write them to see how they built the pistons.
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Unread postAuthor: rcman50166 » Mon Sep 14, 2009 9:43 pm

I have a full unviersity machine shop, CNC mill, lathe, drills, saws, torch, mig welder etc. The problem is just the fact that raw materials cost so much, Schedule 80 everything is expensive, but still cheaper than steel
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Unread postAuthor: Technician1002 » Mon Sep 14, 2009 11:15 pm

rcman50166 wrote:I have a full unviersity machine shop, CNC mill, lathe, drills, saws, torch, mig welder etc. The problem is just the fact that raw materials cost so much, Schedule 80 everything is expensive, but still cheaper than steel


It fully depends on where you shop. I should post a price list for the little cannon. I belive the entire bill for that cannon came to under $50 for a nice steel cannon that tosses shirts 200 feet. The tank is under $5 if you decide to buy one new and use the contents. It is safe at 100 PSI and still has the original safety relief valve. I think the relief valve opens at more than 300 PIS, but I haven't tested it.

My large cannon is also steel and uses a free tank. The pipe nipple is the most expensive component in the cannon. If I didn't spend so much on a wide selection of barrels for it, the basic cannon can be fully built for less than $100.

It's a free tank, a $35 custom cut and threaded nipple, plastic at $3.75/lb, 2 70 cent o rings, a goodwill fireplace poker, a golfball, a $6.00 garden kneeling foam pad, a few pieces of brazing rod and welding rod, welding gas, a few parts for the fill and gauge, and several cans of spray paint.

There is no reason for it to be expensive. I'm starting my 3 inch. I already have a free obsolete propane tank (7 gallon) with the old style POL valve they will no longer refill, another fireplace tool for the shaft, the HDPE, etc. I'm shopping for a 3 inch pipe nipple 24 inches long. This is my high expense item for this cannon.

A $400 dollar budget, access to all those tools, and a little resourcefulness, and your set. You should have more than enough left over for lunch for the team. Steel is much higher impact resistant and fatique resistant than PVC. I highly recommend it. As a bonus, my steel 2 inch cannon is about 1/3 the weight of my 2.5 inch PVC cannon. I'll plan on weighing them both later. One is bulky and awkward. The other is a pleasure to use.

I do fully agree that schedlule 80 PVC parts are very expensive. My Dragon Cannon has several PVC fittings that were over $30 each.
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I took a good look at your GGDT. The little cannon above outperforms that cannon on 100 PSI. Using the same shirt weight, the larger barrel and smaller valve provides a higher launch speed.

I think if you figure out how to eliminate the huge dead space, things will work better. Lighter pistons open faster. Are you sure that dead space is really that big?

GGDT below shows a more powerful launch using about 10% of the air volume. If you want multi shots, work on effeciency and gas consumption per shot. I could launch 100 shirts with the same supply you use to launch 10. My actual chamber is smaller than shown. I used round numbers for size. I don't have the actual size at work.

I took the liberty of modifying your design and plugging the numbers into GGDT. This mod will use less than 1/5th the air per shot, add 50 FPS to the shirt and cut the KE in the piston down to 1/4 so the possibility of breakage is much less. I enlarged the barrel so the cross section on the shirt is much better for the air launch effeciency and better flight. Overall this reduced the cost. A faux chamber can be added from a form tube for cosmetics if desired.

@ spuddytyrant; The full size cannon used in the contest was able to tag the retired numbers above the 300 section of the Rose Garden Arena in Portland OR on just 35 PSI. :D
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Attachments
Small shirt.jpg
GGDT screen shot. Small shirt launch tube on the small QDV launcher.
Shirt Mod.jpg
Design modified for a 6 inch long coaxial chamber, larger barrel, and smaller valve. Excess dead space is eliminated. Shirt can park close to the valve.
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