Blow Hard T-Shirt Launcher

[grumpyoldman]

I finally finished the first stage design of my t-shirt launcher. It operates at up to 300 PSI with a 10:1 safety factor. Later I will add a homemade pilot valve, homemade regulator and homemade flow valve.

There were five basic requirements. It had to be safe, inexpensive, hand held, light-weight and, of course, powerful.

Specifications:
• Total Length: 26.5 in.
• Barrel Length: 15 in.
• Chamber Length: 5.25 in.
• Port: 1 5/32 in.
• Weight: 5 lbs. 2 oz.

Safety Features:
• Low Pressure Regulator
• 325 PSI Safety Valve
• Two Pressure Gauges
• All Metal Pressure Chamber

The main chamber is made from A513 DOM carbon steel tubing.
Tubing Specifications:
• O.D.: 3 in.
• Wall: .065 in.
• Yield Strength: 70,000 PSI

According to the equation at http://www.engineersedge.com/pipe_bust_calc.htm, the working pressure is 300 PSI with a 10:1 safety factor.

The chamber ends are 6061 T6 Aluminum, 1 inch thick. It should hold 300 PSI easily.

The chamber is held together by three 5/16 inch, high-strength 1144 Carbon Steel rods with a yield strength of 125,000 PSI. I used a die to thread the ends at 5/16-24. Math below.

Tensile Stress Area of 5/16-24 = 0.0580in2
125,000*0.0580=7250
Area for 2.87 ID Tube = 6.47in2
6.47*300PSI=1941 lb. Force
7250*3=21750/1941 = 11:1 Safety Factor

The barrel is 2.5 inch schedule 40 PVC.

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I had a friend of mine shoot the t-shirt while I took the video. We measured it at 224 feet.

[youtube][/youtube]

[c11man]

Wow that looks nice. Can tell a lot of time and effort when into the design to make sure it was safe and worked properly! Did you have any trouble sealing up the threaded rods? What regulator is that

Looks to be a handful

[grumpyoldman]

Wow that looks nice. Can tell a lot of time and effort when into the design to make sure it was safe and worked properly! Did you have any trouble sealing up the threaded rods? What regulator is that

Looks to be a handful

Thanks!

The rods are sealed using high pressure sealing washers. Seals up to 8,500 PSI. They work great. http://www.mcmaster.com/#catalog/120/3240/

The regulator is from China. The ad says 0 to 150 PSI but it goes a little over 300 PSI. http://www.aliexpress.com/item/Paintbal ... 67042.html

[mark.f]

Nice work! It wasn't readily apparent how it was held together until I looked at the rear plug and saw the lock nuts. Then of course I re-read the article and realized I missed that note...

A little note on the spacer which holds the piston centered in the large portion of the chamber, since the photo's resolution is a little low... is that aluminum (or a softer metal than steel)? I would be worried about scratching channels into the inside of the chamber.

Looks great though. I can really tell you spent your time designing this.

[grumpyoldman]

A little note on the spacer which holds the piston centered in the large portion of the chamber, since the photo's resolution is a little low... is that aluminum (or a softer metal than steel)? I would be worried about scratching channels into the inside of the chamber.

Good catch. The stabilizer was made from standard threaded rods. I'm going to change that to using eye bolts with the eye going over the holding rods.

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I would also like to say, I could not have built this without the help of SpudFiles and all the smart and creative people that contribute. I didn't know anything about pneumatics when I first came here. Hat tips to JSR, BTB, Gun Freak, Gippeto, Ragnarok, mark.f, Tech, D_Hall, Fnord, Goats spudz, GonzoInferno and all the rest. A special thanks to PCGUY for creating this incredible forum and to all the moderators. Thanks to all.

[Gippeto]

Palmers female stabilizer might help streamline the look a little...

http://co2reg.com/index.php/regulators/ ... black.html

Can be had in lower pressure versions as well.

Regards,

Al

[wyz2285]

I must say I'm impressed! And it has been a while since I got impressed by a cannon here :p
Switch to eye bolts is a smart call otherwise I'm worried about the guide bolts scratch the chamber too.
Kinda weird to have the regulator on board instead of on the bottle but I guess that's no big deal.

[grumpyoldman]

Thanks, Gippeto. It means a lot getting recognized by my fellow spudders!

Kinda weird to have the regulator on board instead of on the bottle but I guess that's no big deal.

Thanks for the compliment. The reason the regulator is on board is because it leaks when screwed on the CO2 bottle. Cheap Chinese regulator. I'll be adding a homemade regulator later. I wanted to get the main valve working first.

[Brian the brain]

Very, very cool!

I love how you tucked away the safety valve and gauge!
Also, the endplugs and the rods are a nice touch.
Using the rods as guides for the piston is brilliant!

Any chance you'll put two elbows on the blowgun and add a front grip to shoot it minigun style?

[grumpyoldman]

Any chance you'll put two elbows on the blowgun and add a front grip to shoot it minigun style?

There's a very good chance of that.

Using the rods as guides for the piston is brilliant!

Knowing your ability for efficiency and simplicity of design, I had a feeling you would appreciate using the holding rods as guide rods. A lot of my design was inspired by your work on counter balanced valves. The regulator and pilot valve I'm designing for my t-shirt launcher will be CBV's. It will be a few months before the launcher is completed. I probably showcased this too soon but I couldn't resist showing off the main valve.

I'm not sure what the classification of the main valve would be. Would it be classified as a toolie type CBV using a pneumatic pilot?

[Tep]

That's a great looking cannon!

I love the sleek inline design but i wonder if something like this would do as good a job of venting the pilot pressure and look cool on the back with all those dials? Or maybe a push button to launch setup?



http://valves.specialtymfg.com/product/ ... 1-8-fema-2?



Also random question but does it dry fire effectively? It looks like it would need a significant barrel back pressure to compress that spring in between the sealing faces and since the barrel itself wouldn't really provide any back pressure (being significantly larger than the piston it looks like it would just open partially without good pressure.

Could a system like this solve the problem by reducing opening pressure on the front part of the spool? (I think it is a kind of modified spool valve?)

Sorry for the crap drawing on your great diagram! basically the black arrow indicates an oring and the blue arrow indicates air flow through the newly ported area.

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This way when the pilot volume is vented the piston can move fully back without much impediment. I am probably way way wrong with this idea but it's just a thought.

Regards

Tep


edit: can't get images to show right think I've fixed it now.

[Brian the brain]

I'm not sure what the classification of the main valve would be. Would it be classified as a toolie type CBV using a pneumatic pilot?

As far as I can tell it's a 'regular" toolie piston valve.
The only real difference is you're using O-ring in stead of a flat rubber seal.

[jackssmirkingrevenge]

I cannot condone shooting in the direction of a road with passing traffic, while it was just a t-shirt you seem to be impressed by the power, meaning you underestimated the performance - which is usually a recipe for disaster.

Boring safety talk out of the way, fantastic job! - very professionally put together and kudos for sticking with it and actually coming up with a finished products that not only works well but looks great!

[grumpyoldman]

Also random question but does it dry fire effectively? It looks like it would need a significant barrel back pressure to compress that spring in between the sealing faces and since the barrel itself wouldn't really provide any back pressure (being significantly larger than the piston it looks like it would just open partially without good pressure.

Thanks for the suggestions, Tep.
It dry fires great. It doesn't need any back pressure for the piston to completely open. There's a lot of backward force still in action when the back piston suddenly stops. That force is then transferred to the front piston which forces it back. The spring is weak and doesn't need much force for it to compress.

I cannot condone shooting in the direction of a road with passing traffic, while it was just a t-shirt you seem to be impressed by the power, meaning you underestimated the performance - which is usually a recipe for disaster.

Thanks, Jack.
Actually, that wasn't me shooting the cannon. That was a friend of mine and he WAS impressed by the power. I was shooting the video. I had fired the cannon a lot of times before and knew what it could do. I know I shouldn't have allowed him to fire toward a street but we had limited options and I figured nothing would be damaged by a falling t-shirt. Also, thanks for all the advice and encouragement you've given me.