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Formula question and gun design

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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Unread postAuthor: Technician1002 » Wed Jun 17, 2009 8:10 pm

thedeathofall wrote:Okay well thanks for all the help. Especially you Tech.

I should increase bore size, but by how much? I could extend the pump out to 8 inches (max) which would be about a 7.5 inch stroke. I would really like to try to keep the gun as one piece, which is why the built in pump. Trying to carry a stirrup pump on top of everything else may be a problem. (then again, It may be the only solution)


Bye the way, Nice drawing. Well done.


Thanks! As wierd as it sounds, I find making gun designs on microsoft paint, is very relaxing. I can use the system really well, its not complicated, and while it can take a while, it usually turns out okay.

@Daberno

Me neither, which is why I ask :lol:

I was kind of hoping Tech would answer because he seems to know how explain things. Maybe he should change his name to Teach :idea:



Should I increase the bore size.. LOL.. tee hee snork. giggle. Umm, did you mean decrease the bore size? Maybe lengthen the stroke? If so the answer is yes. A bigger bore is more area and more force needed to push it. Sorry I shouldn't laugh at you.. :oops:

Since you spoke of going to a lower pressure, the bore is fine and would work fine for a 1 hand pump. A two hand pump like a regular tire pump can be larger like mine for lower pressure and higher volume per stroke. Mine has a 15 inch stroke, but that would be pretty much impossible to use single handed on a gun instead of on the ground. Guys that are out of shape have trouble with two hands getting it much past 50 PSI.

When I use it on a small chamber, about the best I can push (I'm over 200 Lbs) is just over 100 PSI.

The large volume makes pumping my smaller cannon a fast job with just a couple dozen strokes to get it up to pressure. The small cannon has a chamber volume of 54 cu in.

Hand pumped air rifles (not spring) often use a lever. If we look at the mechanical advantage a few things start to show.

At 1/2 stroke the mechanical advantage is about 2:1. Nice. At the end of the stroke where the pressure is very high, the lever in hitting the end of the stroke is even higher, much like at the end of a gas engine compression stroke, the piston moves little while the crank turns a lot.

http://www.gungarage.com/daisy_rifles.htm

The multi pump rifles on this page are examples. The lever action is operated several times to operate a pump off the lever. The lever is much like that in vise grip pliers that use less force at the end of the high pressure stroke.
Image

Lever action sports pump. Easier end of stroke operation.
Image

On teaching, teaching the willing is fine. Getting a class full of clowns with behavior issues is for the birds. I mentor, not teach. I get paid to do what I like to do. It's much more rewarding.

You get better quality students because they are there to learn. Makes a big difference when teaching (mentoring) those who are trying to learn. They are a real pleasure. :)
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Unread postAuthor: thedeathofall » Thu Jun 18, 2009 1:28 am

Should I increase the bore size.. LOL.. tee hee snork. giggle. Umm, did you mean decrease the bore size? Maybe lengthen the stroke? If so the answer is yes. A bigger bore is more area and more force needed to push it. Sorry I shouldn't laugh at you..


Haha I see my problem, but at the time I was being serious. If i increase bore size, i can increase volume which can decrease number of strokes. I know it will be harder to pump, but would it be worth it?

I may be a high school science geek, but i'm not out of shape. Double day water polo practices take care of that :wink:

Okay so at this point I guess my biggest question is will it work? Is there something I should change, or something you would do different? (mostly speaking to tech on this one)

Oh and i hear you about the teaching thing! you couldn't pay me enough to teach my class :roll:
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Unread postAuthor: Technician1002 » Thu Jun 18, 2009 3:07 pm

thedeathofall wrote:
Should I increase the bore size.. LOL.. tee hee snork. giggle. Umm, did you mean decrease the bore size? Maybe lengthen the stroke? If so the answer is yes. A bigger bore is more area and more force needed to push it. Sorry I shouldn't laugh at you..


Haha I see my problem, but at the time I was being serious. If i increase bore size, i can increase volume which can decrease number of strokes. I know it will be harder to pump, but would it be worth it?

I may be a high school science geek, but i'm not out of shape. Double day water polo practices take care of that :wink:

Okay so at this point I guess my biggest question is will it work? Is there something I should change, or something you would do different? (mostly speaking to tech on this one)

Oh and i hear you about the teaching thing! you couldn't pay me enough to teach my class :roll:


Sorry for laughing. :oops: I assumed what you wanted incorrectly. I stand corrected.

To answer that I need a few more questions answered. What new lower pressure are you aiming for and what force are you comfortable with on repeating strokes. Hit the gym and do some single arm pulling crunches and let me know what weight you can pull comfortably for 50 reps. From there the math is the easy part. For one arm and up to about 60-80 PSI the current diameter looks good to me, but a longer stroke is recommended. You may find a target of 20-40 lbs is in the ball park.

I can hand pump my 700 cu in cannon to 60 PSI on a regular basis with the 1.65 inch pump and the little cannon to 100, but that's using both hands and leaning on it. After that post on the broken pump handle, I'm glad it was the check valve that blew out in my pump.
:D

The reason the 54 cu in tank can reach 100 and the big one only 60 is operator fatigue. I have had it up to 85 PSI by hand for a safety test. I still need to hydrostatic test it to 150.

I'm glad you saw my point on teaching. I don't have the patience of a saint needed to teach today with today's restrictions on discipline. They don't offer combat pay.
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Unread postAuthor: POLAND_SPUD » Thu Jun 18, 2009 4:32 pm

if you mentioned teahcing....

teaching is a nightmare in public schools...
esspecially if your headmaster is a retarded biatch who stopped teaching 15 years ago and she thinks that students are nice and friendly

I preffer to give private lessons - somehow people seem to treat lessons seriously when they have to pay for them :wink:
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Children are the future

unless we stop them now
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Unread postAuthor: thedeathofall » Thu Jun 18, 2009 4:56 pm

Okay well my chamber size will be a little bit more than 11.5 cubic inches, closer to 12.5-13 because of fittings and such.

I am thinking between 80 and 110 PSI. I am still not entirely sure how to program a 3/4 inch QEV in GGDT (anyone have any ideas? I don't have seat/piston diameter).

I happen to have an 8 inch long 3/4 inch pipe nipple. (steel) It has a slightly bigger bore (around 0.82-0.84 inches). I could probably use that for a one hand pump. As far as i can figure, it will take around 55 lbs of force to push 100 PSI of air with a bore that big... That may be too much :? Or I can just buy copper pipe with an ID of 0.5-0.6 inches and do things the shiny way :D

Another option is I can make/buy a pressure container to place in a backpack, as I will need to carry one anyway for ammo. If I can make a stirrup pump that can reach 500 PSI (easy enough), I will just do things that way. But I have to find a regulator.

Last thing,

you have been talking about this 700 cu/inch cannon and I don't think i have seen it. Do you have a link?

@ Poland Spud

HAHA That is like dead on! I have the same problem all the time with my friends. They just don't care about school.
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Unread postAuthor: Technician1002 » Thu Jun 18, 2009 5:06 pm

I have a link. The t shirt cannon is the 700 cubic inch tank cannon.
http://inteltrailblazerschallenge.wikis ... +brag+zone
It's the one the Marshmallow Cannon is a model of.
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Unread postAuthor: thedeathofall » Thu Jun 18, 2009 8:58 pm

UPDATE!!

Okay so i finally decided to just scrap the built in pump idea. I first want to try to make a high(er) pressure stirrup pump. I will use copper, 0.5 or just over 0.5 inch ID.

I will need to get a hold of some kind of gass chamber. Do you think 3 inch or 4 inch galvanized steel can handle 500 psi? If not i will find a paintball Co2 tank.

Because there will be no pump, I (again) redesigned my gun.

And here is the eye candy...

Image

With the trigger in front, i had to shorten my stock, so to keep up the volume, i decided to make it all out of 1 inch pipe and fittings. I also finally decided on an exhaust. It will simply be a blowgun. You know, one with a handle, but still smaller than a pressure washer handle. By moving the trigger, it made my decision easier.

I would really like to build this for summer parties and such, so you can probably expect it to be finished pretty soon.

I also got an idea to hold ammo. A paintball carrier pod can carry quite a few small waterballoons....

Image

cheers!
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