BigBang Express (Now with Dual Spark Video)

Just build a cannon and want to show it off? Post it in here.

Postby BewareOfDog » Tue Jul 18, 2006 10:39 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><b>Originally posted by BigBang</b>
As always, comments and suggestions are welcome.
BigBang
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

BigBang,
You've outdone yourself... again <b>!</b> 8)

What really amazes me, is not that you've managed to construct a seamless double walled chamber, but that you've somehow managed to blend in the transition from chamber to barrel as well.

The paint is flawless, and I love how you've added the metal bracing to keep the base from flexing.

With the "comments" almost out of the way, I would only "suggest" two things:

1.) 3-5 tight layers of Teflon tape on the Union will help tremendously. Not only for smooth assembly, but mostly for ease of disassembly.

The threaded component needs to be pretty tight to seal (and hold) over 30psi... As you are probably well aware of, a Union was never designed to hold pressure, while sandwiching a piece of material between the flanges! ;)

2.) A piece of PET plastic is (in my opinion) the best material for a high pressure burst-disc. Not only does it get the job done, but it also blows completely out of the flanges 99% of the time. - The only downside is that the plastic is severely "curled", making it difficut to install.

Cutting the disc the full width of the flange makes it much easier to align, and this alignment also will ensure that you'll get a good seal. - just don't cut it the full width of the threads as well.


It's <b>always</b> a pleasure to hear from you and also a humbling experience to witness your creations. Thanks, not only for this, but for <b>all</b> of your "contribtions" to these forums.

~DR
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Postby SpudMonster » Tue Jul 18, 2006 11:12 pm

Good Lord! That is one incredible cannon! I agree, the paint, chamber, union, and everything else in incredible. I'm amazed.

Every single time you post, I KNOW it is something that will make me wish I lived in Ohio...
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Postby BiggSauce » Wed Jul 19, 2006 12:43 am

It's been said, but DAMN! So...... clean! Your cannons are truly one of a kind in thier appearance and functionality. You have definitely set the standard for cleanliness and care. I'm sure I speak for us all when I say that I look forward to another post by BigBang.
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Postby joannaardway » Wed Jul 19, 2006 3:36 am

There is no word in my vocabulary that is sufficent for describing this thing...

So, I'll quote instead from George Orwell's 1984: "Double plusgood"
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Postby SAFETYpin » Wed Jul 19, 2006 7:58 am

While its simple amazing to see such craftsmanship and attention to detail, this level is similar to show cars in my opinion. Its to pretty to use, it gone beyond functional to the realm of fashionable. Oh and it looks fantastic, good job. Just one mans opinion.
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Postby markfh11q » Wed Jul 19, 2006 9:20 am

What!? A hybrid that can put a golfball downrange at 700 fps not functional?????

Safetypin your brain back in, please.;)
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Postby BigBang » Wed Jul 19, 2006 11:45 am

Thank you one and all for your kind comments. I only wish my wife viewed my hobby as favorably. (Really, she doesn't complain. She just doesn't "get it" like you do.)

Anyway, to some questions:

Freefall - Yep, the chamber is just silver painted PVC. I painted the chamber silver with the idea that it might reflect sunlight, thereby keeping the inside of the chamber cooler. If I recall correctly, combustion pressure is inversely proportional to initial chamber temperature. So, keeping things cool should increase combustion pressure and overall performance. What do you think?

Salad - <a href="http://www.spudfiles.com/uploader/uploadFiles/SparkPlugs.jpg">HERE</a> is a picture of one of my older sets of "sparkplugs." I just run pretty heavy gauge wire through the elbow and fill it up with lots of epoxy. For further details, check out the link in the original post to the spudfiles discussion of Little Bang.

DR - Thanks for the tip on using teflon tape. I had thought I would use silicone spray lubricant. Have you tried that? Also, the PET burst discs you mention: do you cut them from milk jugs or 2L bottles? And, what mixture have you found them useful for (2X, 3X, 4X...)? And finally, do you use more than one layer of PET for the higher mixes?

Thanks again everyone!

BigBang

P.S. Oh, I almost forgot! DR, did you ever think to mail the flare fittings? I decided not to put the transducer on the hybrid just now. I don't want to be task overloaded when I first try this thing out. But when I get the hang of it I want to add in one of the pressure transducers I got off of EBAY. I'll probably use them first on one of my other "regular" combustions for simplicity.
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Postby airpress » Wed Jul 19, 2006 1:20 pm

Nice work Bigbang.
I like the paintjob.
btw: I can't play the video.
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Postby BewareOfDog » Wed Jul 19, 2006 2:50 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><b>Originally posted by BigBang</b>
DR - Thanks for the tip on using teflon tape. I had thought I would use silicone spray lubricant. Have you tried that?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Anything that remains "wet" is messy. And although there <b>are</b> sprays that dry, leaving a layer of the silicone, the reason that I would favor Teflon tape is:

There are many irregularities in the molded threads; Casting seams, tiny burrs, etc. - The teflon tape adds "thickness" <-- (for lack of a better word?) to the threads and this helps to even things out.

Plus, there's the additional benefit of cost; Teflon tape cost about a buck a roll, whereas some silicone sprays are $5 and up for a small can. ;)

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">
Also, the PET burst discs you mention: do you cut them from milk jugs or 2L bottles?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

2L bottles; There made from polyethylene teraphthalate. Milk jugs, and windshield washer fluid bottles are made out of High Density Polyethylene.

The HDPE is much stronger; A pneumatic burst-disc cannon will blow one layer of PET plastic out at around 80-100psi. A single layer of HDPE will sometimes blow in excess of 150psi.

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">
And, what mixture have you found them useful for (2X, 3X, 4X...)?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

One layer will suffice for up to a 4x mix- Jusy keep in mind that with 3x and higher mixes, the union has to be tightened excessively -to keep it from leaking.

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">
And finally, do you use more than one layer of PET for the higher mixes?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I have, and found that 2 layers of PET will blow out around 160psi. It all depends on whether or not they are installed correctly, and how tight the union is... The plastic is slippery, so it has a tendency to
"slip out" violently, rather than blowing out the center.

Two layers of HDPE? - can anyone say chamber failure? - Just kidding, but... not really. HDPE is incredibly strong and I've used it before, but didn't like the sound that the cannon made; Almost shit my pants!


<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">
P.S. Oh, I almost forgot! DR, did you ever think to mail the flare fittings? I decided not to put the transducer on the hybrid just now. I don't want to be task overloaded when I first try this thing out. But when I get the hang of it I want to add in one of the pressure transducers I got off of EBAY. I'll probably use them first on one of my other "regular" combustions for simplicity.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I keep remembering / forgetting... I'll clean out my garage, and locate those for you. - Sorry about that. :evil:
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Postby KlugeBoy » Thu Jul 20, 2006 10:32 am

That does it. I <u>will</u> be building a hybrid this winter.

That is the cleanest, most professional looking cannon I've seen in a long time. I am simply in awe.

I looked at the reference to "Little Bang" but I'm not real clear on how you built the spark plugs. Could you give a few details?

Also, I'm a little confused as to how you pressurize the chamber and get the fuel mix right. Do you fuel it first and then add air to bring up the pressure to match the fuel?

In any case, your workmanship is superb. I can't wait for some video of this thing in action...
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