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Another Semi-Auto Idea (updated)

A place to ask general spud cannon related questions.
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Unread postAuthor: Hotwired » Wed Sep 26, 2007 6:08 pm

It's not a new concept, the multi-shot I found from my cannon layout was to partially vent the pilot into a secondary pilot chamber: clicky

Skywalker had a peek at the theories and had a go at designing a variant: clicky. I fiddled some diagrams for him and modelled these:

Image

At a more realistc speed:

Image
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Unread postAuthor: grumpy » Thu Sep 27, 2007 8:44 am

hubb017 wrote:
grumpy wrote:tension on the hammer spring has everything to do with the velocity as it controls how hard and how long the hammer keeps the valve open...


Very true...for a paintball marker that utilizes this design to operate the main valve. However, the hammer is going to strike a valve to pilot a larger, main valve. With this setup, the best (and probably only) way to adjust the velocity would be to adjust the pressure of the chamber.


ahh, now i understand what you want to do. possibly with the right combination of springs and by venting all excess air to reset the hammer you might get it to work. the only question i would have is wether or not it would stay open long enough to let the main valve fully open or open fast enough. how much presure are you thinking of to run this at?
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Unread postAuthor: Hubb » Thu Sep 27, 2007 8:55 am

As far as pressure goes, I don't know. I'm not sure on the chamber size either. All because I don't know if the check valve will vent enough air to reset the hammer. I will come up with something and put the numbers into GGDT to see what it predicts.

What I could do is go with a small chamber (maybe a C:B of .25:1) then put high pressure in the chamber. Doing this will allow for 3 things: 1) provide enough pilot pressure to reset the hammer, 2) allow the chamber to refill a lot faster than a larger chamber at a lower volume, and 3) give my cannon an even smaller profile (which is what I'm aiming for, about the same size as my A-5).
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Unread postAuthor: grumpy » Sat Sep 29, 2007 10:58 am

hubb,
i think you should give this a read i found it very interesting.
http://www.spudfiles.com/forums/semi-auto-t160.html
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Unread postAuthor: Hubb » Tue Mar 18, 2008 9:05 pm

I think I feel like kicking up an old thread.

I've been thinking about this concept a lot lately. Some of you may be aware of my next project; pump action launcher. As mentioned above, one of the concerns about this concept was the air coming from the check valve and reseting the hammer. With a pump action, I would not need to do that. I would simply hook the hammer to the pump and manually move the hammer to the sear.

With that said, a new problem has arisen. Say, I have a 1" piston and fill the chamber (and pilot) to 100 psi. This would mean that the hammer would have to deal 100 pounds of force per square inch to open the valve, correct? If this is true, and I use a 1/4" pilot, then I would need 25 pounds of force to open the valve. Being as how the valve is 1", I could get by with using a 1/8" pilot, meaning I would need 12.5 pounds of force.

So, I set my hammer to strike the pilot exhaust with 12.5 pounds of force. The refilling (combined with the check valve's spring) should push the hammer back just enough to cause the check valve to close, right?

Now I need to work out the bounce-back. Thoughts?
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Unread postAuthor: iknowmy3tables » Tue Mar 18, 2008 9:21 pm

yes but I believe that hammer valves are meant to conserve air, so wont using it as a pilot valve make it open to faster bigger and for a longer time thus defeating the purpose
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Unread postAuthor: Hubb » Tue Mar 18, 2008 9:31 pm

In this design, the hammer is used to open the valve. And it will do so very quickly, then close very quickly, thus, conserving air. In theory, it should operate fast enough to not allow any more air out of the chamber that is not necessary.
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Unread postAuthor: Hubb » Sat Mar 22, 2008 3:17 am

Here is an updated picture of what I'm talking about.

Like I said, the biggest concern I have now is the hammer bouncing back and bumping the check valve again, which would cause the valve to open when I don't want it to.

Image
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 22, 2008 3:35 am

Will the hammer be cocked again by the air from the check valve? If not, why bother with a hammer when you can just use a blowgun and open it momentarily?
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Unread postAuthor: Hubb » Sat Mar 22, 2008 3:41 am

I am wanting it to open and close as fast as possible. I plan on using CO2 and would like to conserve it when I can. I figured this way, the piston would open and close so fast, only a minute amount would be wasted.

As far as the pilot air recocking the hammer, it would be nice, but I don't really see that happening. Here's why: Say I fill the chamber to 100psi. The tee piston is going to be about 1 square inch, meaning the hammer will have to hit the check valve at 100 pounds of force to open it. Assuming this is correct, I can cut the check valve in half, say .5 square inch inner surface, and hit it with 50 pounds of force. I just don't see the pilot air being enough to reset a 50 pound spring, or even a 25 pound spring, 3 to 3.5 inches.


My launcher is going to be a pump action type anyway, so I'll just hook the hammer to the pump handle to reset it.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 22, 2008 3:46 am

You should still make your hammer a tight fit though, at least the pilot air will form a pneumatic cushion that should dampen hammer bounce.
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Unread postAuthor: iknowmy3tables » Sat Mar 22, 2008 3:52 pm

I could see that happening if you adjusted it correctly, I don't see your estimates of force working out.
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Unread postAuthor: Hubb » Sat Mar 22, 2008 4:52 pm

Well, it is just a brief (very brief) estimate. I know it will be different, but that gives me a start.

In the original posts, I mentioned having a type of RVA deal on it. That would simply tighten or loosen the hammer spring, causing it to strike the check valve softer or harder. This should eliminate the exact calculation part.
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