T-Shirt Cannon

[SamM]

What you want to have is a "buffer" tank connected to the barrel by large tubing or pipe, i.e. at least 1/2", but 3/4" or 1" is better. The tank should be at least the volume of the barrel.

The buffer tank can be pressurized by small tubing, but you need large tubing from the buffer tank to the barrel.

[cbale2000]

Originally Posted by SamM

What you want to have is a "buffer" tank connected to the barrel by large tubing or pipe, i.e. at least 1/2", but 3/4" or 1" is better. The tank should be at least the volume of the barrel.

The buffer tank can be pressurized by small tubing, but you need large tubing from the buffer tank to the barrel.

This. Keep in mind that smaller tubing will restrict flow, so while your air compressor can be connected using standard 1/8" tubing, everything between the tank and the cannon should be 1". Consequently, you're probably not going to want to use a standard air tank like you might find on AndyMark, look for one with 1" ports (or 1/2" ports and use several of them to merge to a 1", since 1" port air tanks are really hard to find).

[garyk]

My students discovered that a shirt folded to be tight in the barrel shoots much farther than a loose one - although the tight shirt has more friction on the way out, it seals in the barrel much better.

Plastic tanks and barrels have always made me nervous (and I'm not an ME, and I'm sure this has been discussed elsewhere.) An industrial arts teacher at a school 668 is helping suggested copper. It's readily available, and tears rather than breaks up into shrapnel. Yes, it's also more expensive, but it takes a good shine! And it's a good way to prepare future homeowners to solder their water lines.

[snotsdelta]

Originally Posted by cbale2000

This. Keep in mind that smaller tubing will restrict flow, so while your air compressor can be connected using standard 1/8" tubing, everything between the tank and the cannon should be 1". Consequently, you're probably not going to want to use a standard air tank like you might find on AndyMark, look for one with 1" ports (or 1/2" ports and use several of them to merge to a 1", since 1" port air tanks are really hard to find).

This is great info. Thank you! Do you know of any websites that would be good to order from for the tank?

[cbale2000]

Originally Posted by snotsdelta

This is great info. Thank you! Do you know of any websites that would be good to order from for the tank?

Tanks of this type are fairly easy to find on automotive supply websites or Amazon (they're typically used for air horns and other such things). I found this site with a quick search but you'll probably want to search around a bit to see if you can find a tank with the large ports but without a huge capacity (it has to be small enough to be portable after all).

On the note of using PVC, generally speaking I agree that PVC should be avoided, especially for the accumulator (air storage), but to be honest there is far less pressure involved for a much shorter amount of time when using PVC for the barrel of a cannon. IMO if you're really that concerned about it, and can't get a suitable pressure-rated metal tube, build a small polycarbonate (or whatever) box around the bottom half of the barrel to catch shrapnel in the event of a failure. Lots of teams have built PVC t-shirt cannons and no one has died yet (that we know of).

[Daniel_LaFleur]

Originally Posted by cbale2000

On the note of using PVC, generally speaking I agree that PVC should be avoided, especially for the accumulator (air storage), but to be honest there is far less pressure involved for a much shorter amount of time when using PVC for the barrel of a cannon. IMO if you're really that concerned about it, and can't get a suitable pressure-rated metal tube, build a small polycarbonate (or whatever) box around the bottom half of the barrel to catch shrapnel in the event of a failure. Lots of teams have built PVC t-shirt cannons and no one has died yet (that we know of).

*gets up on soapbox*

1> The pressure in the barrel is enough to fire the t-shirt, thus it is enough to fire PVC shards.
2> A box around the lower half of a PVC cannon might help. Are you willing to risk your students (or worse the public) should you be wrong?
3> As to your last line -- does someone need to die to get people to stop using PVC in gas pressure applications?

As an engineer, you need to always understand how safe your product is. T-shirt cannons, by their very nature, will be used near the public. If the t-shirt can reach the crowd, so can shards from a sundered barrel.

JM(NS)HO

*gets off soapbox*