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chamber to volume ratio

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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chamber to volume ratio

Unread postAuthor: nick_b » Tue Apr 22, 2014 6:43 pm

I am sure this question has been asked before so if so I appologize....My students and I are building a coaxial piston air cannon to shoot t-shirts. What is the relationship between chamber volume and barrel volume? currently we are using 4" for the chamber and 3" pvc for the barrel which gives us about .125" space between. I have a reducer I've adapted to go from the 3 down to 2 I can put in the 4" to create more volume in the chamber but how does this affect the force of the air on the shirt since it would be expanding from 2" to 3" as it exited the barrel? We plan to attach this to a robot and automate the process to use at sports games, assemblies, etc...Will upload pics when we get it done. Right now just getting the cannon fundamentals down.
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Re: chamber to volume ratio

Unread postAuthor: jackssmirkingrevenge » Wed Apr 23, 2014 8:20 am

Step 1) Download and install GGDT

Step 2) Plug in your launcher data and play with parameters

Step 3) ????????

Step 4) Profit!
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Re: chamber to volume ratio

Unread postAuthor: Fnord » Wed Apr 23, 2014 9:58 am

Another thing which may be a factor that ggdt doesn't(?) account for, with such a thin chamber you're going to have a large amount of friction between the gasses and the chamber walls. In most guns this can be ignored but in your case it may have a noticeable impact of performance.

nick_b wrote: We plan to attach this to a robot and...

I am glad I am living in an era in which this phrase is uttered occasionally. And also slightly scared.
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