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Short question topic

A place to ask general spud cannon related questions.
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Unread postAuthor: Labtecpower » Thu Jan 27, 2011 2:24 pm

Well well... search and YE shall find..

change your title to searchmaster or something :wink:
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Unread postAuthor: Zeus » Thu Jan 27, 2011 7:09 pm

Or perhaps you could have a terrible memory for everything except Spudfiles and useless facts.

http://www.spudfiles.com/forums/very-simple-bore-hawg-t21970.html
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/sarcasm, /hyperbole
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Unread postAuthor: Labtecpower » Fri Jan 28, 2011 2:55 am

Thank you for digging up that topic.

Before trying that, I'll have to sand the complete inside of the pipe, to remove the formed zinc oxide.
If I dont remove it before working with power tools, i'll get a nasty metal fume fever. that's not something I want.
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Unread postAuthor: beard » Fri Jan 28, 2011 4:20 am

Hi guys , thought that I would chime in with my first post , my first launcher is a metal under / over, 1/4 bsp QEV - http://stevenengineering.com/tech_suppo ... 0AFCAQ.pdf , 9.5 mm ( 3/8 inch ) i.d 3/4inch o.d barrel thats 14 inches long with 1 cubic inch of dead space , piloted by a carpet cleaning shampoo wand trigger that is rated to 1200psi . I run it to 145psi , but have read here that it should be good for 300psi maybe.

My question is if my QEV is any where near the right size? I was thinking about upgrading the the QEV to the same one in half inch bsp or the 3/8 bsp . At the moment it will put a 9.5mm , 3.5 gram bb 6mm into 10mm form ply, with the back starting to split out from 4m away

sorry about the long winded post , I put it into the ggdt but think that the 20fps from changing to 1/2 inch must be wrong.

thanks guys - beard
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Unread postAuthor: jackssmirkingrevenge » Fri Jan 28, 2011 4:49 am

beard wrote:My question is if my QEV is any where near the right size?


Have you measured the internal diameter of the valve output? For example, I have some 1/4" BSP ball valves with an internal diameter significantly bigger than 1/4", to be honest I don't think a bigger valve will make much of a difference and the damage you're reporting is about what you'd expect from such a setup.

If you're looking to increase power, the most obvious and effective parameter to change is pressure. Remember that projectile base area reduces exponentially with calibre reduction, 100 psi in a 1" barrel pushes with 4 times the force of the same pressure in a 1/2" barrel. For this reason, smaller calibres tend to need higher pressures for high performance.

A shock pump is a cheap source of high pressure air, the one linked to can give you at least 400 psi.

You might also consider a longer barrel and larger chamber, but the latter will be correspondingly more difficult to pump and result in a louder shot. It all depends what you want to achieve really.
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Unread postAuthor: beard » Fri Jan 28, 2011 6:43 am

thanks jackssmirkingrevenge , I found that when I went from a 0.177 pellet to the 9.5mm ball, the difference was almost shocking :D

I have been lurking here for a while and the size of QEV to projectile size isn't some thing i have been able to find in the inefficient searches I have done

I have a shock pump that almost exactly the same as the link, but the fitting for the shrader is a screw on , that and I sat on it and broke off the gage - 5 dabs of epoxy filling the hole later and now its good as new. Apart from now I have to use the 150psi gage on my launcher :( It might be time to fix the gage on my pump and try some real power.

A longer barrel and slightly bigger air tank is certainly an idea. I had a paint ball style tank on it previously but found that the 10 minutes that it took to pump up was excessive, mabe try for something in between the 2 .I also learned that the 1/4 bsp comming out of the paintball tank made the QEV honk , after I went to 1/2 and 1/4 fittings on my smaller tank I had no problems and less wasted air.

Also the reason that went with the square style smc valve VS the ususal round type of qev like from festo is that the square type are fully rebuildable and I don't think that the festo type are.

Thanks for the help and when I can get out with my camera theres some launcher / damage pix on the way :D
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Unread postAuthor: irisher » Tue Feb 01, 2011 1:18 am

New question:
What would be fancy title for our hobby if one were to be describing it in brief for something like a collage essay?
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Unread postAuthor: linuxexorcist » Tue Feb 01, 2011 1:40 am

Expanding gas[-based] launch systems
Internal combustion catapults
Compressed gas catapaults
High velocity carbohydrate relocation and destruction devices
do it yourselg flexible projectile choice expanding gas based launching systems (DIYFPCEGBLs for short)

et cetera, mix'n match different pieces, like those word magnet sets
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Unread postAuthor: Gun Freak » Fri Jun 10, 2011 8:09 pm

If I charge a 2 foot 3/4" pipe nipple to 250 psi, how long could I expect the air to last if I discharge unregulated through an unmodded blowgun?
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Unread postAuthor: Technician1002 » Fri Jun 10, 2011 10:10 pm

Just a few milliseconds depending on the bore of the blowgun and orifice and speed of the valve.

Try to model it in GGDT.
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Unread postAuthor: saefroch » Sat Jun 11, 2011 12:19 pm

Infinity, if you have infinitely fine measuring equipment :lol:

Image

Try to use GGDT to find the pressure drop to a very small value.
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Unread postAuthor: Spooky » Wed Jun 29, 2011 7:59 am

I'm not sure how much of a difference this will make but what chamber design would be more efficent.

Using a right right angle end fitting, with slightly less flow.

___________
|
QEV

Or a T fitting with one end capped.

______________
|
QEV

The T fittting due to its shape is slightly more open and so would provide better flow, but will the small amount of air from the back of the capped T reduce perfomance as it 'fights' the air from the rest of the chamber?


Edit: ok this forum deletes the blank spaces I put in to try and illustrate each option. I'm sure someone gets what I mean though.
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Unread postAuthor: Gun Freak » Wed Jun 29, 2011 8:54 am

I get what you mean. I'd try to get a better elbow, but if you wanna use the tee, the performance loss from such a small amount of dead volume would not be noticeable.
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Unread postAuthor: Crna Legija » Wed Jun 29, 2011 9:07 am

Gun Freak wrote:I get what you mean. I'd try to get a better elbow, but if you wanna use the tee, the performance loss from such a small amount of dead volume would not be noticeable.
''


its not realy dead volume but more chamber :lol: .

I doubt you will notice any power gain/lose but better of going with the tee if you can get a peace of all thread that way the chamber will be closer too the barrel.
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Unread postAuthor: Gun Freak » Wed Jun 29, 2011 9:08 am

Oops I thought he was talking about a barrel fitting lol :lol:
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