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GB Semi

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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GB Semi

Unread postAuthor: clide » Tue May 01, 2007 11:36 pm

<b>GB Semi featuring the HEAR valve</b>

This gun is a semi-automatic golf ball gun. It can work on full auto, but it was designed for semi-auto operation.

<b>Main features</b>
o HEAR valve (High Efficiency Auto Reseating valve)
- Sear trigger
- No pilot exhaust
- Prevents complete depressurization of chamber
- Streamlined into the cannon
- performance of a large chamber with a fraction of the air usage
- Full auto capabilities
o Blow forward bolt loading mechanism
- Nearly perfect seal
- Allows for open magazine or hopper
o 4' x 1.5" SDR21 golf ball barrel
o 3' x 2" main chamber
o 3' x 2" secondary chamber
o Modified elbows for close, tight construction
o Heat formed PVC trigger assembly
o My best extended ROF in semi-auto mode is somewhere between 4 and 5 RPS
o Full-auto ROF is about 6 RPS

<b>Pictures</b>
<img src="http://gbcannon.com/pics/gbsemi/fullback.jpg">
<a href="http://gbcannon.com/pics/gbsemi/full.jpg">full view</a>
<a href="http://gbcannon.com/pics/gbsemi/fullbottom.jpg">full view 2</a>
<a href="http://gbcannon.com/pics/gbsemi/front.jpg">full from front</a>
<a href="http://gbcannon.com/pics/gbsemi/fullright.jpg">full from right side</a>
<a href="http://gbcannon.com/pics/gbsemi/fulltop.jpg">full top</a>
<a href="http://gbcannon.com/pics/gbsemi/downbarrel.jpg">looking down barrel</a>
<a href="http://gbcannon.com/pics/gbsemi/elbow.jpg">modded elbow</a>
<a href="http://gbcannon.com/pics/gbsemi/muzzle.jpg">muzzle</a>
<a href="http://gbcannon.com/pics/gbsemi/trigger.jpg">trigger</a>
<a href="http://gbcannon.com/pics/gbsemi/triggerbottom.jpg">bottom of handle</a>
<a href="http://gbcannon.com/pics/gbsemi/triggertop.jpg">top of trigger</a>
<a href="http://gbcannon.com/pics/gbsemi/sear.jpg">sear</a>
<a href="http://gbcannon.com/pics/gbsemi/frontassembly.jpg">sear 2</a>
<a href="http://gbcannon.com/pics/gbsemi/searbottom.jpg">sear bottom</a>
<a href="http://gbcannon.com/pics/gbsemi/bolt.jpg">bolt</a>
<a href="http://gbcannon.com/pics/gbsemi/ballstop.jpg">ball stop</a>
<a href="http://gbcannon.com/pics/gbsemi/ballstop2.jpg">ball stop wire</a>
<a href="http://gbcannon.com/pics/gbsemi/pistonback.jpg">rear of piston</a>
<a href="http://gbcannon.com/pics/gbsemi/pistonfront.jpg">front of piston</a>
<a href="http://gbcannon.com/pics/gbsemi/insiderear.jpg">inside rear piston assembly</a>
<a href="http://gbcannon.com/pics/gbsemi/damage.jpg">damage to plywood</a>
<a href="http://gbcannon.com/pics/gbsemi/damage2.jpg">damage to plywood 2</a>
<a href="http://gbcannon.com/pics/gbsemi/splinters.jpg">splinters</a>

<a href="http://gbcannon.com/pics/gbsemi/gbsemi.gif">gun animation</a>


<b>Video</b>
GB Semi vs. Plywood
[GVideo]http://video.google.com/videoplay?docid=-3322358715669165266[/GVideo]
Some rapid fire action
[GVideo]http://video.google.com/videoplay?docid=-8199052431304386326[/GVideo]
First video
http://video.google.com/videoplay?docid ... 0159918302

Comments:
I fixed the sear for the plywood video, but the trigger started to have some problems so the video starts out a little slow with a lot of cuts, but towards the end I just started pulling the sear directly with my hand and I got some pretty good rapid fire going.

The rapid fire video shows the ROF capabilities after some tweaking. It still needs some more tweaking to get it loading consistently.

The original video shows the performance and some of the problems that I was having initially, most of those issues have been fixed or eliminated, but I'll keep the first video up for reference.

<b>How the valve works</b>
<img src="http://gbcannon.com/pics/gbsemi/hearvalve.png">
The rear part of the valve is slightly larger then the front. This creates a force trying to open the valve that can easily be held back by the sear.
Releasing the sear allows the piston to move back. About the same time it unseals from the barrel, the middle piston seals off the rear section.
The main chamber releases air out the barrel until it reaches a certain fraction of the input pressure as determined by the size of the rear piston and middle piston.
The valve closes and the sear seats back behind the piston to ready it for the next shot.

Update: <a href="http://gbcannon.com/pics/gbsemi/gbsemi.gif">gun animation</a>

<b>How the bolt works</b>
The bolt is a blow forward bolt in the same style as the "Slider" gun. The animation linked to above shows basically how it works. The bolt is plugged on one end with holes in the side to let air in, but in order for the air to get into the holes the bolt must first move forward. Which means that the loading port is sealed off before air is allowed into the barrel.
The ball stop is simply a coat hanger bent so that it can extend into a slot cut into the tee. When the bolt moves forward the wire is bent down slightly.

<b>Performance</b>
Performance isn't too spectacular for the size of gun. Chrony results are around 270 fps at 100 psi. Unfortunately the loading mechanism seems to be decreasing performance significantly. With the same loader/barrel I get around 215 fps with a 2"x10" chamber and a 1" sprinkler valve.

Air usage seems good. My measurement method was to fill the gun with air when the compressor autofill kicked in and count how many times I shot the gun before the autofill kicked in again. In the shots in the first video I got 12 golf balls shot plus 6 accidental extra firings before the compressor kicked in.
For comparison, the 2"x10" chamber only gets 13 fills before the compressor kicks in again.

<b>Background</b>
I started this project with the goal of eliminating the waste of exhausting the pilot chamber air every time. During the course of the project and after several different attempts at various valves, I realized that one design had potential to reduce the greatest air waste of all. That waste is the remaining pressure in the chamber after the projectile has already left the barrel.

Jeez, I didn't think it went back this far, but looking at the Spudtech archive, the series of designs that this evolved from go back over 2 years.

This particular design is probably at least 8 months in the workings. I've had 4 structural failures that resulted in significant reconstructions and I can't tell you how many times I've had to take the dang thing apart to tweak the loading mechanism. It wasn't until this past week that I smartened up and built an adapter to tweak the loading mechanism on a different gun, because this one isn't exactly easy to disassemble and reassemble.


<b>Updates</b>
I still plan on further tweaking to get it running smoother, can't say when I'll get to it though. And if you have any questions about how the valve works or anything, please ask.

5/3/07 - Gun animation added
5/6/07 - New video added
5/6/07 - Cleaned gun, smoothed out edges, updated pictures and added some new pictures.
5/28/07 - Added rapid fire video and updated ROF figures added comments about the full-auto capabilities and deleted some of the old stuff.
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Last edited by clide on Tue Jun 12, 2007 10:30 pm, edited 6 times in total.

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Unread postAuthor: surfbum » Tue May 01, 2007 11:45 pm

:shock:
nice, very innovative
im sure with a redesign or two, you can get the performance up a bit, but as is that is pretty amazing
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Unread postAuthor: hi » Wed May 02, 2007 12:03 am

wow, thats m-azing. its a work of art. It is simple increadible. it may shoot kinda slow, but with tinkering it could be much faster. very very nice. it is an ingeinious valve and i like it very much.
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Unread postAuthor: SpudMonster » Wed May 02, 2007 12:31 am

Image

That cannon is utterly awesome in the biggest sense of the word. Those burst shots show a lot of promise with a fast loading mechanism.
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Unread postAuthor: jackssmirkingrevenge » Wed May 02, 2007 2:26 am

SpudMonster wrote:Image


Lol! While I *didn't* cream my pants, I'm also very impressed :D
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Unread postAuthor: rna_duelers » Wed May 02, 2007 4:50 am

Indeed Awesome!

But the rubberbands on it and some of the PVC parts looked like they were hacked at with a butterknife.A littlebit of cleaning and sanding could fix that but :wink: .

There is nothing wrong with those speeds I might say 260+FPS is by no means lousy.Love that no waste of air to actuate th valve.

Can't wait to see the bugs fixed in it.Thats going to happen isn't it?
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Last edited by rna_duelers on Wed May 02, 2007 5:30 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Wed May 02, 2007 4:55 am

rna_duelers wrote:There is nothing wrong with nose speeds I might say 260+FPS is by no means lousy.


That's almost 110 ft/lbs assuming a 45 gram golf ball, meaning it's got the same muzzle energy as a 0.22 rimfire rifle :shock:

Let's see some rapid-fire on-target video, pretty please?
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Unread postAuthor: clide » Wed May 02, 2007 10:31 am

If I can think of a decent target then I am all over that (shooting golf balls into the great blue yonder gets expensive with a fast firing gun). Unfortunately no targets that I have available come to mind. Since I lack a CO2 setup, I need to fire it close to the house. That means the target can't be strong enough to bounce the balls. I suppose I could just use a thin sheet of wood or that corrugated roofing in the Slider video. Anybody else have better ideas?
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Unread postAuthor: jackssmirkingrevenge » Wed May 02, 2007 11:10 am

Some 1/2 inch ply sheet would be wonderful :D I'm guessing 110 ft/lbs would make short work of it, without any rebounds.
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Unread postAuthor: SpudMonster » Wed May 02, 2007 6:07 pm

jackssmirkingrevenge wrote:
SpudMonster wrote:Image


Lol! While I *didn't* cream my pants, I'm also very impressed :D



I'm just in a crude mood lately.

Any type of thin plywood would work well for a target. 1/2' plywood would be like butter for a golfball going 260 FPS.
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Unread postAuthor: VH_man » Wed May 02, 2007 8:25 pm

you should sell plans for those valves to some spud-gun entrepreneur and make it so EVERYONE can have one of them. thats what this contest is aobut. being reveloutionary. and youve done it. congrats. how much pressure is on that sear, btw, it has to be ALOT.
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Unread postAuthor: Hotwired » Wed May 02, 2007 8:56 pm

It doesn't have to be...

If the sear side piston is the same size as the barrel side then there is zero force. Make one side slightly bigger and there will be force that way.

The force will be the pressure acting on the area of the larger piston minus that of the smaller piston and you can adjust both.
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Unread postAuthor: sjog » Wed May 02, 2007 9:09 pm

My target is two layers 1/2 +3/4" ply , the back stop is 4 layers of rubber roofing. I use gb's .If I shoot just the rubber , golf balls will go thru. The ply wood slows the balls and the rubber stops the balls dead. I get to reuse the gb's.
You can see my target on my contest entry video, bottom of the page.
L7 gbl
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Unread postAuthor: clide » Wed May 02, 2007 9:35 pm

Thanks for the targets suggestions sjog and jack. Looks like I'll be going with some 1/2" ply and possibly something behind it if they are coming through too fast.

As for the force on the sear Hotwire is correct. The front piston diameter is just slightly smaller than the rear and this creates just a little bit of force trying to open the valve when in the closed position. I would say it is somewhere around 10 pounds. And just like a normal piston valve it has the jump in force once it begins to open.

I'm working on an animation of the gun's internals that will hopefully help people understand how it works. Should have it up by tomorrow.

Thanks for all the compliments.
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Unread postAuthor: Velocity » Wed May 02, 2007 9:44 pm

...wow... that gun just blew my mind!

Thats crazy all of the bells and whistles that it has on it! It really looks nice.

What exactly is the secondary air chamber for? Faster reloading perhaps?
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