SpudFiles

Spudchukker III - Venting Piston Hybrid



Hey guys,

I finally got around to making the showcase post for my hybrid since I feel it has more-or-less reached completion.

You can find the build log for the cannon here: http://www.spudfiles.com/hybrid-cannons/topic25087.html

As mentioned in the other thread, I took major inspiration from SpudBlaster15's TBMA V2.0 and MrCrowley's Mjollnir, and credit goes to them for the basic design of this cannon, although I worked most of the specifics out myself.

Specifications:

Fuel: Propane + Air @ ~7X
Metering: Manometric (0.644psi propane per mix number)
Chamber: 12" x 2" Galvanized iron nipple + 2" 90 degree Galvanized iron elbow
Barrel: 1.5" x 48" EMT Counduit
Valve: Unbalanced Barrel Sealing Spool Valve with machined steel piston and pilot venting port w/ heavy rubber gasket bumper
Ignition: 30Kv Igniter circuit (from Ultimatespudgun.com)
Spark Gap: NGK-CR6E Extended Spark Plug
Misc: Custom 3D printed pistol grip and spool knob

More specifics can be found in the build log.

Below you will find some drawings and renders, note that they are missing the aforementioned pistol grip, barrel support, and ignition system. Being the crafty folks you are, I trust you can come up with that stuff yourself

Overview: For best results, right-click and "view image"


Cross-Section:

Note: For those who want to know, all fittings are 2" galvanized iron except for the two nipples located at the sealing face of the barrel and associated bushings which are 1.5". The piston port is a 3/4" NPT to solder joint adapter.

Piston Operation(After Ignition):


Renders:


Valve closed:


Valve open:


Obligatory Damage Pics:
Fresh 3/4" plywood:



Videos:
[youtube][/youtube]
[youtube][/youtube]

Sorry for lack of footage / pictures. Once I got busy with work during the summer, which eventually led to school in the fall, I didn't have a lot of time to set up any video shoots or "procure" targets.

EDIT:
Found some vids a friend sent me from his iPhone, made a gif:

TL;DR I made a cool potato gun

Comments and criticism much appreciated!

Looks good! Although maybe you could copy some of the pictures over in the build log to here, or take some eye-candy ones?

Glad to see some more hybrids being made... or really, something other than pneumatics being made.

That's quite a punch! You might was to consider some sort of muzzle brake, or at least some padding on the shoulder thing that goes up

Very clean build, looks like you did your research and it came out nice!

As anti-hybrid as I am, there is no denying the greatness of this creation! I love your renderings too, those are quite eyegasmic, I must say.

As JSR previously suggested, I believe some proper rounds are in order... This thing will do some serious damage. But I understand that you are busy

I'm really happy to see that this cannon made it all the way to the finish line after being so long in the makes. But I guess that automatically comes with making a cannon of such extreme complexity. Things like this don't happen often in the spudding world. I commend you!!

Gun Freak wrote:As anti-hybrid as I am, there is no denying the greatness of this creation! I love your renderings too, those are quite eyegasmic, I must say.

Welll... you know that this can still be fired as a pneumatic by piloting through the rear ball valve, right?

It could be a way to lubricate your passage into the hybrid world

As a pure pneumatic, it is quite weak, though I estimate it has about a 100 yard range with a high arc. One could always start with a decent sized steel piston-pneumatic with a bigger chamber, and then you'd be only one spark-plug away from a pretty big manometric hybrid!

That is to be expected, you're firing at much lower pressure and with cooler and therefore much denser gas as a pure pneumatic. It's good to have the option of less powerful hassle free shots though

edit: I note that my first post here was more or less the same as the comments I made in the original thread. Ah well, at least I'm consistent

jackssmirkingrevenge wrote:

Gun Freak wrote:As anti-hybrid as I am, there is no denying the greatness of this creation! I love your renderings too, those are quite eyegasmic, I must say.

Welll... you know that this can still be fired as a pneumatic by piloting through the rear ball valve, right?

It could be a way to lubricate your passage into the hybrid world

I understand that, but if I wanted a pneumatic piston valve cannon I'd build just that

Why is everything a sexual innuendo with you

I gave similar praise to SB15 and Crowley when they made piston hybrids, but we all know what little effect they had on motivating me to convert to the dark side

Noice! Awesome work even getting it finished, I can't seem to get passed half finished with projects simpler than this. Props on the rendering, video, 3D printing, and a working piston hybrid.

+ Rep

How did you get rid of the ridges in the metal nipple? Where the larger o rings of the piston ride.

Gun Freak wrote:Why is everything a sexual innuendo with you

What I say is ambiguous, you're the one who interprets it wrongly

A woman walks into a bar and asks for a double entendre, so the barman gives her one.

CS wrote:Noice! Awesome work even getting it finished, I can't seem to get passed half finished with projects simpler than this. Props on the rendering, video, 3D printing, and a working piston hybrid.

+ Rep

How did you get rid of the ridges in the metal nipple? Where the larger o rings of the piston ride.

Thanks for the props! I got lucky, the nipple I bought for the piston to slide in was smooth to start with. I guess that particular manufacturer smoothed out the weld seam from factory.

Great to see this finished! Love the renderings as well, they'll come in handy when helping people build similar cannons. If you want, upload some renderings with your username on them to save us having to attribute the renderings to you if we use them elsewhere on the forum (or in youtube videos).

I have no clue about hybrids really, so excuse me if this question is very stupid...

Does the fuel ignition first ignite to cause hight pressures, and then from then on it acts like a pneumatic cannon?

Yes, sort of. The difference is that a pneumatic piston valve cannon can store the chamber pressure over long periods of time, so you can manually pilot the valve (fire the cannon) by venting the air pressure behind the piston. With a hybrid, the high pressures only last a fraction of a second so the venting of the air behind the piston has to be done automatically. This is the job of the spool valve in this design (the small o-ring at the back); the piston forced back by chamber pressure unseats this valve and vents the air.

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