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Semi-Auto Pneumatic Bolt

A place to ask general spud cannon related questions.
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How's my design?

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Semi-Auto Pneumatic Bolt

Unread postAuthor: Flash » Wed Dec 12, 2007 9:13 pm

This is my first post here, but I've done some research on the paintball guns, bbmgs, and pneumatic launchers on this and other sites. I've also had some experience modifying Nerf guns from nerfhaven.com.

Ok, here's my design. Its based off the blow forward BB bolt, used by JSR, with some incorporations from the Smart Parts Ion and Shocker. Instead of using a spring to return the bolt, I decided to use a two way valve. The valve simultaneously vents the air used to move the bolt back and allows air to flow to the bolt.[


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Comments? See anything that could be improved?
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Unread postAuthor: ShowNoMercy » Wed Dec 12, 2007 9:49 pm

How does the air used to propel the paintball get behind it?
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Unread postAuthor: Flash » Wed Dec 12, 2007 11:34 pm

The bolt is hollow. The rod keeps air from entering through the bolt until the bolt is pushed ahead of the rod, creating a gap, which allows air to flow. This air the pushes the paintball through the barrel until it exits.

Or by it, did you mean the bolt. In that case, click on the pictures to get a better view of the bottom section. As the trigger moves back, the o-ring on the far right moves forward also allowing air to escape out of the firing chamber, through the tube fitting, and behind the bolt.
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Unread postAuthor: TwitchTheAussie » Thu Dec 13, 2007 12:51 am

JSR is this an unwedded bastard (proper words dont harass me) son of yours? No offence :P
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 13, 2007 1:54 am

TwitchTheAussie wrote:JSR is this an unwedded bastard (proper words dont harass me) son of yours? No offence :P


I have no offspring that I know of (with the possible exception of a few sprogs somewhere in the Ukraine :roll: :D ) and the blow forward bolt is by no means an original idea of mine, so that's unlikely :P

Flash, your design looks like it would work, however I would be concerned about the limited flow, you'd have to use pretty high pressure to yield significant power.
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Unread postAuthor: Novacastrian » Thu Dec 13, 2007 2:02 am

Like what kind of pressure? My guess unreged co2.
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Unread postAuthor: Hailfire753 » Thu Dec 13, 2007 2:19 am

Hmm, that is very similar to how some paintball valves work, so like JSR said, you will need high pressure with your current design. The other option is to simply increase the flow. I don't know how good you are at machining, and what tools you have at your disposal, but it looks a lot more difficult then a QEV and JSR-style blow foward.
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Unread postAuthor: Flash » Fri Dec 14, 2007 4:05 pm

jackssmirkingrevenge wrote:Flash, your design looks like it would work, however I would be concerned about the limited flow, you'd have to use pretty high pressure to yield significant power.


Yeah, the design doesn't have the most flow, but then again the diagram isn't completely to scale. I guess I could enlarge the bottom chamber so its about 3/4 the size of the bolt.

I've been testing roughly how much air would be needed to move the bolt. With a nerf gun modified with a .5" PVC barrel and a small air tank at less than 15 psi, I could move a AA battery the length of the barrel. If I were to make the bolt out of something light, like PETG, I shouldn't need a ton of air.

Hailfire753 wrote:Hmm, that is very similar to how some paintball valves work, so like JSR said, you will need high pressure with your current design. The other option is to simply increase the flow. I don't know how good you are at machining, and what tools you have at your disposal, but it looks a lot more difficult then a QEV and JSR-style blow foward.


I have some experience using a dremel, jigsaw, and a handheld drill. I realized that if I want to make this work well, I'll probably need to build something like this first.

Novacastrian wrote:Like what kind of pressure? My guess unreged co2.


I want to be able to make this work with a portable 100 psi tank.
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Unread postAuthor: iknowmy3tables » Fri Dec 14, 2007 5:34 pm

welcome
hmm a person from the relm of nerf modders
well we spudders are a similar breed to nerf gunners but the thing that separates us is power so without some significant chambers and valves were not satisfied with something thats only effective at 20 feet

you got something with a heck of a lot of seals I have plenty of router, band saw, and drill press experience, and I wouldn't try to make it,
for starters:
I'd simply buy a 3way valve and make a larger petruding chamber

However I like the design from the stand point that it resets the bolt with the valve, hmm I think I got a way of spudifying it...
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Unread postAuthor: al-xg » Fri Dec 14, 2007 5:59 pm

This might be what iknowmy3tables was thinking of, but i'd have the valve pressurised from the front(using a 3port valve or slide valve in initial postion for piloting later)and fill the back through a flap or mini check valve, it would seal like a reversed QEV, the surface area at the back of the bolt being smaller than at the front.
Activate the 3port valve and the air inlet is cut off and the air infront of the bolt is vented.
Have the valve srpingloaded back so as you let go the inlet is opened and the cycle starts again.
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Last edited by al-xg on Fri Dec 14, 2007 6:19 pm, edited 1 time in total.
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Unread postAuthor: iknowmy3tables » Fri Dec 14, 2007 6:03 pm

got it now with a more conventional spuding twist
Image
like this hmm but now its not much diffrent from the original blow forward, at least it uses less of the air in the blast to close the bolt

hey flash why are you nerf gun people so big with using tube seals what are the advantages and disadvantages to the real deal orings
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Unread postAuthor: al-xg » Fri Dec 14, 2007 6:10 pm

oh maybe not then :)
For larger scale, a QEV could be used to vent the front of the bolt, it would just have to be conected to the 3port throught the pilot end and to the front of the bolt through the chamber port.
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Unread postAuthor: Flash » Fri Dec 14, 2007 10:31 pm

al-xg wrote:This might be what iknowmy3tables was thinking of, but i'd have the valve pressurised from the front(using a 3port valve or slide valve in initial postion for piloting later)and fill the back through a flap or mini check valve, it would seal like a reversed QEV, the surface area at the back of the bolt being smaller than at the front.
Activate the 3port valve and the air inlet is cut off and the air infront of the bolt is vented.
Have the valve srpingloaded back so as you let go the inlet is opened and the cycle starts again.


I'm having a kinda hard time visualizing that. Do you think you could post a quick diagram? And how do slider valves and reversed QEVs work?

iknowmy3tables wrote:got it now with a more conventional spuding twist...like this hmm but now its not much diffrent from the original blow forward, at least it uses less of the air in the blast to close the bolt

hey flash why are you nerf gun people so big with using tube seals what are the advantages and disadvantages to the real deal orings


That design looks intriguing, but can you explain how the air flow changes between the chamber and the QEV?

As for the o-ring thing, Nerf guns require a tank small enough so that it can be quickly filled with a handheld pump. If the tank is too big, then it becomes impractical to pump when using it in games. Because of the limited air supply, the valves and barrels have to be extremely efficient at sealing, thus the use of o-rings. With spud guns you can get away with a slightly less than perfect seal because of the sheer size of it.

iknowmy3tables wrote:you got something with a heck of a lot of seals I have plenty of router, band saw, and drill press experience, and I wouldn't try to make it,
for starters:
I'd simply buy a 3way valve and make a larger petruding chamber


I gotta start getting machining experience somewhere, why not this? How do commercial three way valves work? Do you think it has a high enough flow rate and opening time for a paintball gun?

If I get the bolt to work, I want to try to make this field legal and fast enough to keep up with a Tippmann A5. Keeping it compact is also a priority so I don't think I'll have the chamber protrude unless the size interferes with the performance.
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Unread postAuthor: al-xg » Sun Dec 16, 2007 4:40 pm

New drawing in progress....
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Last edited by al-xg on Sun Dec 16, 2007 6:57 pm, edited 1 time in total.
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Unread postAuthor: Flash » Sun Dec 16, 2007 6:29 pm

How does the air vent from the front of the bolt? Another drawing would be great.
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