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Bolt Piston

A place to ask general spud cannon related questions.
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Do you think this will work?

Yes
7
78%
No
2
22%
 
Total votes : 9
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Bolt Piston

Unread postAuthor: Atlantis » Tue Feb 07, 2006 5:50 pm

I was checking out the "Slider Semi-Auto" and I think I found a way to combine a piston with a bolt. I don't see any reason for this not to work. If I tried mixing this with Clyde's input/exhaust combo, it might be capable of Semi-Auto firing. Tell me what you think.
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Unread postAuthor: beebs111 » Tue Feb 07, 2006 5:56 pm

:?: i dont get it
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Unread postAuthor: CS » Tue Feb 07, 2006 8:12 pm

NICE DESIGN!!!
I dont know if such a design has been used, I would imange since its such a convient design, yet I dont recall such a design. There would be more effeicent ways of sealing the chamber and ways of air entering barrel. Ill make some animated .gif's in a bit, but im currently Im working on my reasearch paper and Spudfiles store in flash. I love it! In fact I dont think any one has done this, instead use seperate air cylinders to drive reloading mechanism. This could also be used in a auto combustion design. Im being overan with concepts, ARG! Good work...
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Unread postAuthor: cardinals08 » Tue Feb 07, 2006 8:15 pm

man, I wish I could come up with things like this, I dont know much about spudding yet to be able to come up with improvements to anything. This design looks awesome.
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Unread postAuthor: K40T1C » Tue Feb 07, 2006 8:19 pm

Im not quite sure wat it is right now but im sure that after pimpmann posts some gifs, that itll all come to me and i will praise youre name for your genius... ANYWHO
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Unread postAuthor: Atlantis » Wed Feb 08, 2006 4:10 pm

I'm glad you guys like it. I think I may have found a way to make it even better. Sorry the pic is so rough, I had to make it in a hurry, I'm sure you get it though. The air in this design pushes on the piston directly instead of the relativley small area of the bolt. The bolt now just has an open end which differs from Clyde's design. The bolt rests against a flat rubber surface for a good seal. I came up with an idea similiar to this about 2 months which can be found here.

http://www.spudfiles.com/forums/viewtopic.php?t=1132&

NOW FOR A BIT OF IRONY....I've never built a pneumatic anything. LOL

P.S. I would like to see you design an Auto-Combustion, that would be sweet.
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Unread postAuthor: clide » Mon Feb 20, 2006 5:36 pm

I think OJHSpyro posted a similar design on spudtech at some point.

It should work to an extent, but something you need to be very aware of is the surface areas exposed to pressure and what pressures they are exposed to.

Remember that a typical piston valve snaps open so quickly because it exposes more surface area as it begins to open.

In this design, particularly the last one. It doesn't have the increase in surface area, and your pilot pressure will be increasing because of the moving piston, while your chamber pressure would rapidly be dropping because of the relatively large port for air to exit the chamber.

In my experience with such valves, they have a hard time opening all the way or have issues with piston bounce back, both situations would not be good for a system that relies on piston movement to close off a loading port.

The first design could be made to have the increase in surface area, but you would need to design it so the outside ring surface area is significantly larger than the surface area of the valve porting.

And extending the black body up to the piston in both designs seems unnecessary and seems like it could cause some problems with that small volume between it and the piston acting like an air spring.

So basically, I think it would work, but you need to take some considerations with the dimensions for it to work well.
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Unread postAuthor: Atlantis » Mon Feb 20, 2006 8:13 pm

If you would care to draw something with the correct dimensions for me I would truly appreciate it. One thing about piston valves is the Pilot Surface-Chamber Surface ratios.
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Unread postAuthor: clide » Mon Feb 20, 2006 11:33 pm

Well the only thing that is required is that the cross-sectional area of the outer ring is greater than the cross-sectional area of the bolt, otherwise it wouldn't hold itself shut, of course that is required to not be choking flow as well.

As for what is needed to make it work well, that's a tricker question that depends quite heavily on projectile weight and the size of the pilot valve, and probably the pilot volume too.

Your best bet would be a GGDT model, plugging in the values you plan on using for the size of gun you want, keeping in mind that what you are trying to find is sensitive to projectile weight and pilot exhaust size. (You might want to have the values lower than what you plan on using to ensure adequate opening). Set the valve type to chamber sealing and set the seat to whatever size the OD of the bolt is(where it seals of the chamber). You can then see what piston diameter is required to not cause oscillations of the piston by looking at the valve position graph while modeling different diameters. Now that diameter you get is not the diameter of the piston itself, but the cross-sectional area of the outer ring should be equal to the area of a circle of that diameter..

Hopefully you followed me through that, if not just ask and I'll try to clarify.
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Unread postAuthor: Atlantis » Tue Feb 21, 2006 1:57 am

I'll have to check that program out I've never used it before, sounds useful, and YES I know where to get it. I'm not going for max performance here, since my friends nor I know the true power of a good pneumatic we will still be impressed. Wow double deja vu.
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Unread postAuthor: clide » Wed Feb 22, 2006 11:32 pm

Well, since the bolt is connected to the piston, any oscillation will be greatly magnified by the fact that you will rapidly lose a lot of pressure out the loading port as it moves back, also shooting out any projectiles you have in a clip.

So basically my concern is not about the performance loss of an oscillating valve, but the performance loss of an oscillating bolt, which may be pretty significant as well as troublesome to the loading process.
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