SpudFiles

my first time using ggdt how dose it work i dont know all the info it wants the barrle 1in the chamber 2in the siton 2in ? why wont it work

More details!

The GGDT website will tell you what you need to enter for each parameter. If you are confused by a particular parameter, ask us in this thread. At the moment you have given us no details.

dead volume? outer diameter? seat diameter? piston mass? projectile friction?

http://www.thehalls-in-bfe.com/GGDT/

Valve -> Dead Volume
With the notable exception of co-axial barrel sealed designs, virtually all other gun designs possess "wasted volume" downstream of the valve seal but upstream of the barrel breech. This volume is defined here.

Dead volume: the volume between the valve and the projectile.

Reservoir -> Outer Diameter
GGDT assumes that the reservoir is a right cylinder with a longitudinal void in it. The outer diameter input corresponds to the outer diameter of the reservoir cylinder. Note that we are talking about the outer diameter of the air volume, not the outer diameter of the piece of pipe you might use to actually make such a reservoir; it is instead the inner diameter of that pipe (which defines the outer diameter of the reservoir volume). Clear as mud?

Outer diameter: This is the diameter of your chamber. So if it's 2" PVC, don't put 2", that's only a nomindal diameter. Measure the inside pipe diameter (don't include the walls of the pipe) and put it here.

Note: If your design is NOT a coaxial, you put the OUTER diameter as the chamber diameter and the INNER diameter as 0. If your design IS a coaxial, you put OUTER diameter as your chamber diameter and INNER diameter as the outside diameter of the barrel.

Valve -> Seat Diameter
The valve's seal seat diameter. In layman terms? If you've got a "1 inch valve" odds are pretty darn good that you're gonna want to enter 1 inch here.

Diameter of the seat. Simple as that. If the opening on your valve is 1" you put 1" here. The seat is what the piston seals against/the size of the opening of your valve to the barrel.

Piston mass: Mass of the piston. How much it weighs.

Projectile friction you can ignore, just leave it at 0.5PSI unless you have a very tight fitting projectile.

What valve are you using?

edit: If you're using a sprinkler valve, here are the parameters to use:

Ok, GGDT inputs for 1" and 3/4" Orbit Watermaster valves

Valve Type: Barrel Seal
Seat Diam: .95" in a 3/4"...1.1" in a 1" (diameter measured at where the seat actually seals if anyone is wondering where that came from)
Piston Diam: 1.8"
Piston Mass: .8 oz
Vent diam: .05" with solenoid, .1" to .2" depending on the blowgun. .2" usually requires modification on most blowguns.
Pilot volume: 1in³
Dead vol: up to the end of the threads. 1.5in³ in 3/4", 2.2in³ in 1"

Got that from here:
http://www.spudfiles.com/spudtech_archi ... t&start=40

co-axil barrle sealing piston