General Questions on PSI

  • Thread starter dekoi
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  • #1
dekoi

Main Question or Discussion Point

For recreational/educational purposes, i am looking into building a small cannon which would shoot projectiles of about 1.0 cm in diameter. I would like to gather some information regarding the PSI needed to reach high velocities (roughly 100 m/s) with a projectile of mass around 7 grams. Should CO2 be used as the pressurized gas? Would anyone provide a rough outline on how i would go about building high pressure, welding the barrel, etc. ?

Thanks. :smile:
 

Answers and Replies

  • #2
T@P
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on a somewhat unrelated note i noticed that you could fill a wine bottle with vinegar and baking powder, quickly stuff the cork in and when the cork flew out it went maybe 30-40 feet if i did it fast enough.

lol i know this isnt really answering your question, and truthfully i dont really know how to make your cannon-ish thing but i thought it migt at least tell you what to expect. and its a terrible mess if you want to try doing it, do it outside where you dont have to clean up too much.
 
  • #3
dekoi
T@P said:
on a somewhat unrelated note i noticed that you could fill a wine bottle with vinegar and baking powder, quickly stuff the cork in and when the cork flew out it went maybe 30-40 feet if i did it fast enough.

lol i know this isnt really answering your question, and truthfully i dont really know how to make your cannon-ish thing but i thought it migt at least tell you what to expect. and its a terrible mess if you want to try doing it, do it outside where you dont have to clean up too much.
Hmm. Well thanks for trying. :rofl:
 
  • #4
dekoi
No physics majors able to help?
 
  • #5
chroot
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Well, 100 psi (for example) would apply about 50 pounds of force to an object that's about a half square-inch in size. 50 pounds of force is about 200 newtons. Solving f=ma, an object of 7 grams mass would experience an initial acceleration of about 32,000 m/s^2. If you could sustain that pressure for about three milliseconds, you'd get your projectile up to 100 m/s.

You'll have to choose your energy source wisely. Most potato cannons just use hairspray and a simple piezo-electric igniter like those used on gas grills. You might have to do an experiment to see exactly how much the burning hairspray expands, and therefore how big the combustion chamber would have to be, etc.

Keep in mind that 100 m/s is a pretty good fraction of the speed that most bullets have when leaving the barrel of a gun -- be careful with this device, no matter how you choose to build it.

- Warren
 
  • #6
dekoi
chroot said:
Well, 100 psi (for example) would apply about 50 pounds of force to an object that's about a half square-inch in size. 50 pounds of force is about 200 newtons. Solving f=ma, an object of 7 grams mass would experience an initial acceleration of about 32,000 m/s^2. If you could sustain that pressure for about three milliseconds, you'd get your projectile up to 100 m/s.

You'll have to choose your energy source wisely. Most potato cannons just use hairspray and a simple piezo-electric igniter like those used on gas grills. You might have to do an experiment to see exactly how much the burning hairspray expands, and therefore how big the combustion chamber would have to be, etc.

Keep in mind that 100 m/s is a pretty good fraction of the speed that most bullets have when leaving the barrel of a gun -- be careful with this device, no matter how you choose to build it.

- Warren
Thank you chroot. Helpful like always.

Regarding the energy source, would you mind giving me some examples of energy sources which i could experiment/research on? From what i have found, the general energy sources used for these potatoe cannons (even though i dont plan on shooting big projectiles such as potatoes) are compressed air and combustion (like you mentioned). Question: how would i go about building air pressure in a tank? I understand i must use a compressor, although i would assume practical compressors are too weak.
Also a question: what PSI do paintball guns exert on the shots? What speeds do these paintballs reach and approximately of what mass are they?
 
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