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GGDT/HGDT Request Thread

A place to ask general spud cannon related questions.
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Unread postAuthor: Atattack » Wed Aug 31, 2011 9:26 pm

I think this is a pneumatic ?, not a GGDT ?
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Unread postAuthor: Gun Freak » Wed Aug 31, 2011 9:41 pm

Atattack wrote:I think this is a pneumatic ?, not a GGDT ?

I'm very well aware.
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Unread postAuthor: MrCrowley » Wed Aug 31, 2011 9:48 pm

Thanks for the PM Atattack, but I have merged your second topic with this one again because chamber:barrel ratio questions are best answered by GGDT outputs. With pneumatics, there never really has been a general consensus on C:B ratios although some people may suggest particular ratios that generally work well.

The best way to figure out the dimensions of your cannon is by using GGDT.

At the beginning of this topic I wrote "Any topics asking things like what size chamber/barrel they should have on their cannon or how powerful their cannon may be, will be merged here for someone to compute an output for them". It is just easier if all similar topics are merged here since they all use GGDT to some degree.

Cheers :)
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Unread postAuthor: mark.f » Fri Sep 02, 2011 10:03 pm

This is just a slight niggle, but GGDT/HGDT should work on nearly all operating systems, either on Windows natively or in WINE.

As has been mentioned countless times, run it with administrator privileges on Windows Vista and above for it to operate correctly.

If you have a Mac, Hackintosh, or run Linux, install WINE with MacPorts on Mac, and with your default package manager on Linux.

After installed, browse to your "Drive C:" directory (usually /home/{your_username}/.wine/drive_c), and extract the GGDT and HGDT directories here.

Then, go here to get MSVBVM60.DLL, which should be extracted to the "{drive C directory}\windows\system32" directory. You can also copy the DLL from a working Windows installation.

After that, simply open a terminal in the GGDT or HGDT directory and type in "wine (h/g)dt.exe" to start.

So far, I haven't had any problems running on Debian.
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Unread postAuthor: Lockednloaded » Tue Sep 06, 2011 9:20 pm

2.5" x 10" tennis ball barrel
1" x 8" chamber
2oz tennis ball with a CD of about .6

Valve:
valve type - generic
# of valves - 1
Flow Coef. - 5
Seat Diam - 0.75 in
Open Time - 20 ms
Dwell Time - 999 ms
Dead Vol - 1 in3

Can I get screenshots at 200, 300, and 700 psi?
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Unread postAuthor: D_Hall » Wed Sep 07, 2011 12:01 am

jackssmirkingrevenge wrote:This raises an interesting question, maybe D_Hall can weigh in on the matter - does GGDT assume this friction only until the projectile starts to move, or along the whole time the projectile is in the barrel? If it's the former case, it could be used to simulate the addition of a detent to the system...

GGDT assumes that level of friction until the projectile starts to move. Once the projectile starts to move, the level of friction is cut in half and this new value is used the whole time the projectile is in the barrel.
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Unread postAuthor: Technician1002 » Wed Sep 07, 2011 12:29 am

Atattack wrote:So wouldn't a solenoid valve remain open until the gas vents the chamber so wouldn't it be the same as a burst disk for this?


Some solenoid valves will re-close when the chamber is small and the pilot flow is too low. This can result in the pilot pressure being high in relation to the rapidly dropping chamber pressure. The most common evidence of this is when a sprinkler valve honks as it closes, opens, closes, etc.
Most modified sprinkler valves do not have this issue. It is the reason to modify one.

A big difference between a sprinkler valve and burst disk is the flow path when open. The sprinkler valve has much more restriction to fast flow than an open straight pipe.
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Unread postAuthor: Crna Legija » Wed Sep 07, 2011 1:35 am

For Lockednloaded. IDK how tight they are in the barrel so I just left it at 0.5
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Unread postAuthor: Lockednloaded » Wed Sep 07, 2011 9:52 pm

Thanks a bunch,
well its a very tight barrel, but those numbers look very low compared to what im actually seeing... I'm getting a 6s hangtime when i fire straight up at about 300psi
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Unread postAuthor: Technician1002 » Thu Sep 08, 2011 12:00 am

With a higher valve CV, and chamber size, you should be able to get a much longer hang time. The shot below was launched at just under 100 PSI. A 2 inch chamber will hold 4X the air of the 1 inch chamber. A 2 inch valve can be fitted to the 2 inch chamber for a higher valve CV.
http://www.youtube.com/watch?v=s0l5t7D0FDM
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Yet another GGDT question

Unread postAuthor: High-PSI » Sun Nov 13, 2011 2:04 pm

Hey Guys,

Since day one, I have not been able to get GGDT to run. I have loaded on three separate computers. It absolutely, positively, will NOT run. I have spent hours trying to get the files to unzip and open to no avail.

Is there any hope?

I am running Vista on my main computer and 7 on my netbook.

I am at my whits end.

Matt
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Unread postAuthor: Labtecpower » Sun Nov 13, 2011 2:06 pm

Have you tried right click> run as admin?
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Unread postAuthor: High-PSI » Sun Nov 13, 2011 3:15 pm

OK, thanks LOADS!

I right clicked on every file and finally came up with one that had "Run as administrator" selection. It works! Man, I owe you a lunch! :)

So, a couple questions, then;

Tank inner diameter and outer diameter. What does that mean? It cannot mean wall thickness of tank. I assume it means maximum tank diameter and the diameter of the tank is it enters the valve? Is that correct? These numbers drastically affect the output. So, I am curious about that.

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Unread postAuthor: jackssmirkingrevenge » Sun Nov 13, 2011 3:17 pm

High-PSI wrote:Tank inner diameter and outer diameter. What does that mean? It cannot mean wall thickness of tank. I assume it means maximum tank diameter and the diameter of the tank is it enters the valve? Is that correct? These numbers drastically affect the output. So, I am curious about that.


It refers to a coaxial layout, where it would be inner diameter of the chamber and outer diameter of your barrel. In your case, with an inline layout, inner diameter should be zero.
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Unread postAuthor: Labtecpower » Sun Nov 13, 2011 3:36 pm

OK, thanks LOADS!


No problem, I haven't found out myself :wink:

Man, I owe you a lunch! :)


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