Coke can to 150 meters?

[erdos4d]

Hi Everyone,

I am new here and would like to ask some questions about a build I am attempting soon. I have a 120PSI compressor and I want to make a pneumatic launcher that can sling a coke can (standard 12oz/330ml) about 150 meters. I am using a coke can because that seems like a really cheap shot cup for smaller stuff, but let's assume that it will be full of coke for this discussion, so should weigh about 0.35 kilo. I will have to check this in real life but I have access to some PVC rated at 180PSI that seems a good fit (67.5mm internal diameter with google saying the can is 66mm). My plan is to get a piece of barrel about 2 meters long and make a piston design with a chamber coming from 110mm PVC. I read on the wiki that the C:B ratio on a pneumatic should be low, like 0.2 or 0.3, so I will size accordingly.

My questions:

1) Based on your experience, can a pneumatic like I describe reasonably do this? I am having a really hard time guessing how the can will fly, so I'm worried it will produce a lot of drag and I won't be able to make the range target I have.

2) Do you agree with a small C:B ratio or should I beef it up?

3) How important is piston open speed in this? A 110mm piston is somewhat heavy and my only options are wood and maybe bondo, so I'm worried it will be too slow and mess up the launcher's functioning. Then again, coke cans are heavy too.

Thanks for your help!

[jackssmirkingrevenge]

Wecome to the forum!

1) Based on your experience, can a pneumatic like I describe reasonably do this? I am having a really hard time guessing how the can will fly, so I'm worried it will produce a lot of drag and I won't be able to make the range target I have.

I suggest you download Gas Gun Design Tool in order to be able to optimize your design by altering the variables and seeing how performance is affected.

I have modeled your project quickly here:

The assumption here is that the can will not tumble, and the predicted range is a little over 200 meters. Of course a tumbling projectile will lose velocity more quickly and therefore range will be shorter.

2) Do you agree with a small C:B ratio or should I beef it up?

A low C:B ratio means your launcher will be more efficient, but it might not have the performance you want. Again, punch the numbers in GGDT and you will have a good idea of how changing the variables will affect performance.

3) How important is piston open speed in this? A 110mm piston is somewhat heavy and my only options are wood and maybe bondo, so I'm worried it will be too slow and mess up the launcher's functioning. Then again, coke cans are heavy too.

Have a look at this thread on casting pistons from epoxy, with a bit of thought you can make your own that will be both very right fitting and also lightweight, although especially with PVC construction a rubber bumper of some sort is going to be essential.

[jackssmirkingrevenge]

double post please delete

[erdos4d]

Thank you jackssmirkingrevenge! You really helped me a lot, I appreciate the time you spent on modeling my problem.

I wanted to ask you, if you know, how do you install GGDT? When I try to just unzip the files and run the executable it gives me a warning message that it can't find various files. Is there maybe a trick I'm not doing?

[jackssmirkingrevenge]

No worries, that's what this forum is for have you tried right-clicking on the GGDT icon and selecting "Run as Administrator"? That usually solves the issue.