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WIP: 1.5" Porting Handheld Piston Hybrid (DAMAGE VIDS)

Built a hybrid 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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Unread postAuthor: c11man » Thu Jun 24, 2010 3:05 pm

if it does fail just get a peice of plastic or metal and cut it to size and drill a hole in the middle, thats what i have done several times so that is exactly the right size

also you might want to sand down the 2inch nipple so that is smoother for the orings to seal on

and filling twice with air might get annoying
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Unread postAuthor: SpudBlaster15 » Thu Jun 24, 2010 3:19 pm

c11man wrote:if it does fail just get a peice of plastic or metal and cut it to size and drill a hole in the middle, thats what i have done several times so that is exactly the right size


That would probably work well. The large steel washer I'm using is pretty close to the inside diameter of the pipe, but there is some room to work with.

also you might want to sand down the 2inch nipple so that is smoother for the orings to seal on


I have sanded it with some 320 grit sandpaper, and with a bit of silicone grease, the piston slides nicely. I test pressurized the pilot chamber, and there was no leak through into the chamber after 20 minutes, so the seal is satisfactory.

and filling twice with air might get annoying


It may, and I might look into a close loop filling system that would allow me to fill both the chamber and pilot to separate pressures using one input valve. Future considerations though.
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Unread postAuthor: Moonbogg » Fri Jun 25, 2010 1:14 am

Damn, thats a nice piece of kit. Very nice job. Well, theres no turning back now. Piston hybrids are coming of age and are set to become more common. Thanks for showing your internals. This helps me understand more about just how this design functions.
Consider incorporating a check valve attached to the piston somehow. I heard someone else mention this idea before. This would allow you to pressurize once through the pilot, pressurizing the pilot and chamber with no combustion force being able to enter the pilot area. It might not be able to be incorporated with this design, I don't know. Just thought i'd throw it out there. Very good job!
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Unread postAuthor: SpudBlaster15 » Fri Jun 25, 2010 1:57 am

Moonbogg wrote:Consider incorporating a check valve attached to the piston somehow. I heard someone else mention this idea before. This would allow you to pressurize once through the pilot, pressurizing the pilot and chamber with no combustion force being able to enter the pilot area.


I thought about that, but in the end decided that I want to be able to set the pilot opening pressure independently of the chamber pressure. One fill point would be nice, but I'm not sure it would be beneficial for this design. Thanks for the suggestion though. Your input is always appreciated.
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Unread postAuthor: ramses » Fri Jun 25, 2010 12:29 pm

How did you get the pipe the piston seals against into the tee? did you thread the other "half" of the bushing?
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Unread postAuthor: SpudBlaster15 » Sun Jun 27, 2010 1:00 am

Yesterday, I had a slight incident with the barrel that lead to me rebuilding the entire assembly. The new barrel is 6ft of 1.5" solid core ABS, with the first 1ft sleeved with couplers. It's considerably heavier than the original barrel, so a support has been added.

Also, the small fan was not moving air as efficiently as the launcher requires, so the larger, much more powerful fan from my ABS combustion has replaced it. I hate the mounting system, but it will do for now.

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The launcher has yet to fire, mostly due to my difficulties finding a suitable testing site. Tomorrow I hope to attempt the first test firing, and if all goes well, this projectile will be fired at an interesting target.

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So long as everything works as it should, the 160g battery slug should give me ~3200ft-lbs of muzzle energy at a 5x mix. Possibly the most energy ever obtained from a shoulder fired spudgun? I'm a bit nervous just thinking about it.
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Unread postAuthor: CpTn_lAw » Sun Jun 27, 2010 5:34 am

Aren't you afraid of the hit in your shoulder? I mean, first tests obviously are fired remotely, but after a while you're gonna shoot it as i is meant to.
I would be scared...
I remember of the hole punch i shot and...i took me off my feet. Might i add, my hybrid does not come close to the level of energies you're playing with...
Be carefull
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Unread postAuthor: Crna Legija » Sun Jun 27, 2010 8:36 am

Mabye start with something a bit lighter, i get a pretty big kick shooting 50g of lead at 300psi and i have a 1 1/4 inch thick wood stock.

what dia is you meter/stock?

At least get a vid of you shooting, if you get knocked over put it on Funniest home videos :lol:
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Unread postAuthor: spudtyrrant » Sun Jun 27, 2010 9:27 am

SpudBlaster15 wrote:So long as everything works as it should, the 160g battery slug should give me ~3200ft-lbs of muzzle energy at a 5x mix. Possibly the most energy ever obtained from a shoulder fired spudgun?
well technically......you'll probably need to go heavier to obtain that record
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Unread postAuthor: SpudFarm » Sun Jun 27, 2010 11:56 am

Good job SB, might I ask what the "incident" was?

You should try to shoot a light projectile at a watermelon. It is damn fun!

I guess this cannon reaches higher energies, it's a hipfired cannon though.
[youtube]http://www.youtube.com/watch?v=sdFK5eVmZ3o[/youtube]

Oh, and don't you have a worry about something causing the piston to come out of the tee and into your eye? That would be quite nasty.
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Unread postAuthor: SpudBlaster15 » Sun Jun 27, 2010 1:49 pm

CpTn_lAw wrote:Aren't you afraid of the hit in your shoulder? I mean, first tests obviously are fired remotely, but after a while you're gonna shoot it as i is meant to.
I would be scared...


Thanks to the substantial mass of the launcher (30lbs, or ~13.6kg), the recoil energy with even very heavy rounds won't be massive. Accounting for the mass of the propellant gas, I'm getting a figure of ~55ft-lbs for the 160g battery slug, which is about the same value my previous burst disk hybrid produced with the same round. I managed that with no issues, so I'm not really expecting any surprises here.

-_- wrote:Mabye start with something a bit lighter, i get a pretty big kick shooting 50g of lead at 300psi and i have a 1 1/4 inch thick wood stock.


I'm not going to fire the battery right away; some frozen potatoes or similar will likely be tried first.

-_- wrote:what dia is you meter/stock?

At least get a vid of you shooting, if you get knocked over put it on Funniest home videos


The stock is 1/2", but I have some leftover foam padding that will likely be added to the back as on my previous hybrid.

It would be pretty funny to see me get knocked over by the recoil force; maybe I'll cast some full bore lead slugs and see if I can manage that. :lol:

spudtyrrant wrote:well technically......you'll probably need to go heavier to obtain that record


I suppose I could bolt on a barrel with 4x the cross sectional area and twice the length of my current unit, then maybe throw in an oversized low pressure combustion chamber, maybe sell it for an order of magnitude profit... but that's nothing interesting. How do you even shoulder fire a 10ft long 3" barrel anyway?

SpudFarm wrote:Good job SB, might I ask what the "incident" was?


A friend was over examining the cannon, and he tried to pick the 30lb launcher up by the end of the barrel. :roll: The ABS threaded adapter cracked at the threads, which doesn't surprise me, since the barrel assembly was 3 years old (Originally from this cannon) and had seen probably close to a thousand shots on various launchers.

SpudFarm wrote:You should try to shoot a light projectile at a watermelon. It is damn fun!


What would you consider "light"? Golf ball core? Frozen potato? I suppose it would be interesting to try with marble buckshot.

SpudFarm wrote:Oh, and don't you have a worry about something causing the piston to come out of the tee and into your eye? That would be quite nasty.


There's over an inch of rubber between the piston and the endcap, and even without a bumper, I doubt the lightweight ABS piston would have sufficient energy to cause catastrophic failure of the iron cap. I know Fnord managed to crack a Sch40 iron reducer, but he was using a mechanical spring with no bumper, and an aluminum piston which weighed nearly half a pound.

Oops, I just realized that I completely missed a question from further back in the thread. Sorry ramses.

ramses wrote:How did you get the pipe the piston seals against into the tee? did you thread the other "half" of the bushing?


Yes, the pipe is threaded into the back half of the bushing, but since I wasn't able to reach anything close to full thread depth, it is also sealed with JB weld. I was going to silver solder it instead, but I currently don't have access to a torch that is capable of heating sufficiently quickly.
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Unread postAuthor: SpudBlaster15 » Fri Jul 02, 2010 7:53 pm

I finally got around to firing a few shots the other day, and I ran into a few issues, which was expected.

The main issue was caused by the 100PSI pop off valve I was using on the pilot chamber. Although it works as the manufacturer intended and opens at exactly the specified pressure, it reseals at approximately 80-85PSI, which prevents most of the air in the pilot chamber from venting to the atmosphere. With the initial pilot pressure at 60PSI, approximately 40PSI remained after the piston had opened and reseated.

Now, this caused two issues. One, the valve did not have the lightning fast opening time or long dwell duration that it should, and performance suffered noticeably. The other more serious issue involved piston rebound. With the valve open and chamber pressure dropping, the pressurized air behind the piston propelled it back into the seat with sufficient force to cut cleanly through the sealing face, and slightly damage the face of the ABS piston body.

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To solve these issues, I needed a pilot valve that would open a short instance after piston movement began, vent rapidly to the atmosphere, and remain open until the pressure had dropped to atmospheric. I threw around ideas involving a variable surface area pop off valve, a spring loaded hammer valve, and even a small piston valve with a locking sear, before finally coming up with likely the simplest and best solution: a spool valve type design.

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By effectively connecting the pilot valve's sealing face to the main piston, the valve is forced open by even the slightest piston movement, venting the pilot chamber and allowing the piston to open at maximum velocity. Because the valve doesn't reseal until the piston returns to a closed position, pressure cannot linger in the pilot volume. With such a high opening speed, the piston does rebound off the rubber bumper with sufficient force to reseat itself, but the impact with the seat is no longer energetic enough to damage the sealing face.

The construction of the valve spool is quite simple. A combination of 1/4" UNC setscrews and nuts hold 2 overlapping steel right angle brackets in place, and a 3.5" long 1/4" UNC Grade 5 steel bolt passes through the brackets' shared mounting point and is held in place by nuts. The spacing between the spool valve seal and the piston is adjustable via nuts, though it is a pain in the ass to adjust, and was rather time consuming to initially set up properly.

Oh, and the spool valve seal is just a tapered rubber washer.

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This setup required the repositioning of a threaded hole in the endcap, which is why you see so many fittings in the end. The 1/8" schrader valve tapped directly into the cap is just an epoxy filled plug, and will eventually be replaced with either a proper plug, or something useful.

To help eliminate sealing face issues, the thin butyl rubber washers have been replaced with a 5/16" thick sealing face made from a much harder and stiffer rubber compound. It's much more durable than the previous face, but still seals well.

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Lightweight ABS piston, spool valve pilot venting, low piston to seat diameter ratio, optimized valve flow path... fastest opening, highest flow hybrid piston valve ever? :D

Additionally, I've eliminated the fan setup, and returned to the pressurized air venting setup which was used on my previous hybrid cannons. The electronics overcomplicated the setup, and as the piston reseals the barrel after each shot, venting with a fan was rather impractical. The large ball valve on the end of the chamber will allow the pressurized vent system to work just as it did on my burst disk launchers.

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With the fan gone, I now have an open 2" solvent weld socket on the front of the barrel support. Couple 90* street elbows and an under barrel ammo holder? We'll see... Anyone have some better ideas?
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Last edited by SpudBlaster15 on Sat Jul 03, 2010 4:23 am, edited 1 time in total.
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Unread postAuthor: SpudBlaster15 » Sat Jul 03, 2010 2:36 am

Sorry for the triple post, but I finally shot some video of the launcher today. With the upgraded pilot design, the valve's performance seems to rival that of my burst disk hybrid cannons. Quite impressive.

Marble buckshot has turned out to be good ammo. I fired 20 1/2" marbles at 2 different targets, and the results were pretty much what I expected. HGDT estimates the velocity to be somewhere around 1100fps; I'm not really sure if they were supersonic. The YouTube video titles are mostly advertising.

Enjoy.

[youtube]http://www.youtube.com/watch?v=cljJSxDSrMk[/youtube]

[youtube]http://www.youtube.com/watch?v=qDSunqXnfv8[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Sat Jul 03, 2010 2:39 am

Great stuff, gotta love shotgun rounds :D how about a fistfull of 0.177" steel BBs?
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Unread postAuthor: SpudBlaster15 » Sat Jul 03, 2010 2:44 am

I was planning to fire a couple hundred steel BBs at a large block of ballistics gel, as I recently acquired about 2lbs of gelatin powder. Hopefully that gets done within the next couple days. Should look pretty spectacular on video.
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