2 inch piston cannon comment please

[spudtyrrant]

specs:
valve:barrel sealing piston
operating pressure:10-120psi
piston: 2 inch solid pvc piston
power:ggdt says 400 fps with a golfball but my chrony says 635fps(75psi) 8)
distance: i haven't been able to measure a golfball yet but with a nerf minivortex i would guess i get about 300 yards at 80psi
i used the same chamber design as MrCrowley's golfball gun but i made a separate valve design for this cannon
without further ado i present to you my pride and joy
http://www.seehere.com/spudtyrrant/my_golfball_gun/

[kiwi of nitro]

Looks awesome, any pictures of the piston's innards?

[spudtyrrant]

no not yet but i will get some i don't want to ruin anything by accident before i take it to school tomorrow

edit: its my freshmen year were doing pressure to volume laws and i thought this would be a perfect project

[kiwi of nitro]

Oh right, thats what I'm doing too, it's my sophomore year, I'm building a few for a physics and tech class.

[daniel323]

nice.. looks comfortable to hold for a big cannon

[King_TaTer]

Ahhh, now I see what the "Hey MrCrowley" thread was for. Looks pretty good, Way better that Crowley's. Ha ha no I'm only kidding, but your is almost as pretty. Just needs a paint job I think.

Pretty good performance I'd say too. Got any plywood lying around?

[spudtyrrant]

Ahhh, now I see what the "Hey MrCrowley" thread was for. Looks pretty good, Way better that Crowley's. Ha ha no I'm only kidding, but your is almost as pretty. Just needs a paint job I think.

Pretty good performance I'd say too. Got any plywood lying around?

its got a paintjob lol it used to be white. yes yes i do have some plywood around "holy plywood" if you know what i mean

[Mitchza89]

Absolutely beautiful job mate. I love it the valve set up, it looks so neat.

Not many people can give Crowley a run for his money .

[Technician1002]

specs:
valve:barrel sealing piston
operating pressure:10-120psi
piston: 2 inch solid pvc piston
power:ggdt says 400 fps with a golfball but my chrony says 635fps 8)

What is the valve orifice (barrel opening) size?

I have seen shooting chronographs error when mist , wadding or other higher speed stuff triggers it. If you can borrow a high speed camera or use a wire break chronograph, you should be able to confirm the speed.

A wire break chronograph can be assembled with a sound card to use Audacity to time the wire breaks to get transit time.

[spudtyrrant]

"What is the valve orifice (barrel opening) size?

I have seen shooting chronographs error when mist , wadding or other higher speed stuff triggers it. If you can borrow a high speed camera or use a wire break chronograph, you should be able to confirm the speed.

A wire break chronograph can be assembled with a sound card to use Audacity to time the wire breaks to get transit time"

the porting is 1.5" it was built in a 2 inch tee i just shot another shot through my chrony and got 615fps i am using sdr21 i don't need wadding and have no mist

[Technician1002]

"What is the valve orifice (barrel opening) size?

I have seen shooting chronographs error when mist , wadding or other higher speed stuff triggers it. If you can borrow a high speed camera or use a wire break chronograph, you should be able to confirm the speed.

A wire break chronograph can be assembled with a sound card to use Audacity to time the wire breaks to get transit time"

the porting is 1.5" it was built in a 2 inch tee i just shot another shot through my chrony and got 615fps i am using sdr21 i don't need wadding and have no mist

I would believe the chronograph. In testing air cannons, I have found larger bore cannons seem to get better FPS. Using a 2 inch valve and a 2.5 inch barrel got an apple to 882 FPS for me under 100 PSI. My 1 inch marshmallow cannon is only getting 600 FPS with the 1 inch barrel and marshmallows. I hope to get the barrel trimmed for best speed soon.

I am not familiar with ggdt. What is it?

[spudtyrrant]

"I am not familiar with ggdt. What is it?"

ggdt is the gas gun design tool it is used for designing air powered(or other inert gas) cannons it tells you the predicted fps and ft/lbs and gives you other useful info

edit:if any of you want to share pictures with no ads seehere.com is a really good website

[Technician1002]

"I am not familiar with ggdt. What is it?"

ggdt is the gas gun design tool it is used for designing air powered(or other inert gas) cannons it tells you the predicted fps and ft/lbs and gives you other useful info

edit:if any of you want to share pictures with no ads seehere.com is a really good website

Thanks. I didn't see ggdt in a quick Google search. Where can it be found? Is it free or open source?

Even better than a photo is a good high speed video. We clocked an apple at 882 FPS and then shot this. The measure in the background was to verify the launch speed until someone left a water bottle in the path.
[youtube][/youtube]
The video is from a 2 inch quick dump valve cannon using a 2.5 inch barrel. We used ~80 PSI. My thread on spudfiles explains how the valve works.

Many of my photos are in the forum under projects on http://www.crazybuilders.com. Their forum permits posting photos, sounds, etc. Some of my other photos are on wikispaces.

[spudtyrrant]

nice cannon i see you have a workshop. i wish i had my own workshop but alas i am a 15 year old lol maybe when i am older i'll have one comparable but that is a long way off lol

[daberno123]

@Technician1002
Here is the wiki link for the page on GGDT. You can download it off D_Hall's site. There's a link in the article to his site.

@spudtyrrant
Very nice gun, I'm also a fan of Crowley's launchers, especially that pilot setup. However, I don't see how GGDT managed to get so far off. Would you mind posting a screenshot of how you entered it into GGDT? I'd trust a chrony over GGDT but...
If you only got that reading once on the chrony, it could easily be a false one. My chrony has sometimes given me erroneous results when I was too close to the chrony or had bad lighting. A difference of over 200 fps is a BIG margin. Of course, if you've consistently gotten results near that then there must be something wrong in how you defined it in GGDT.