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Hybrid Q's From Crowley

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: Novacastrian » Thu Jan 31, 2008 4:02 am

I believe the term used is "Foosball". (No offence intended)
RNA- i tried to link pics of a chamber i have but photo bucket is undergoing site maintenance.
For me to machine a chamber as you stated ( i also remember you mentioning this a while back) would involve about 12 hours solid work. I can only currently perform machining during work hours-(oxymoron i know).
I will start a thread pertaining to the chamber in question when Photobucket finishes polishing it's knob.
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Unread postAuthor: rna_duelers » Thu Jan 31, 2008 4:07 am

Ok the pictures would be sweet,and 12 hours of machining...Wow,all that over making a hollow sphere?What type of job do you have that allows you to use all these machining tools?
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Unread postAuthor: Novacastrian » Thu Jan 31, 2008 4:30 am

rna_duelers wrote:Ok the pictures would be sweet,and 12 hours of machining...Wow,all that over making a hollow sphere?What type of job do you have that allows you to sue all these machining tools?


The jobs that i work with on a day to day basis include machining of mainly non-ferrous materials, these include but are not limited to- Stainless steel, Brass, Aluminum, Nylons and PTFE's.
It takes a long while to learn how each different material acts under machining, like does the stuff melt, deform, creep etc.
I would never say that i could do "Anything" in regards to machining and or making a specific item- however given the time and resources my employer thinks otherwise. :x I am mainly employed as a "jobber", someone that can supposedly fix anything (within reason).
As for me "sueing" all the tools- i make most or modify currently existing tools to suit the needs of jobs that we accept- we don't say no to much.

A spherical chamber would have to be made out of some "exotic" materia, metal is hard to cut with a form tool!
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Unread postAuthor: rna_duelers » Thu Jan 31, 2008 6:14 am

Well sue me for spelling it wrong,worst joke ever. . . . :D

So basically you can use any type of milling/machining tool as long as you have had practice,that would be very useful and I imagine it would be a [female doggy] sometimes to work with some of the materials.I remember using lathes and milling machines back in school and it was hard enough from using steel and brass because you had to change how you cut it etc.Your job would be hard,but rewarding right?
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Unread postAuthor: Novacastrian » Thu Jan 31, 2008 6:43 am

rna_duelers wrote:Well sue me for spelling it wrong,worst joke ever. . . . :D

So basically you can use any type of milling/machining tool as long as you have had practice,that would be very useful and I imagine it would be a [female doggy] sometimes to work with some of the materials.I remember using lathes and milling machines back in school and it was hard enough from using steel and brass because you had to change how you cut it etc.Your job would be hard,but rewarding right?


I really hate blowing whatever horn i may have, however my job isn't the easiest one out there- nor is it near the hardest.
My only "expertise" as such has come from years of working with different materials, as such i am in a very different position than most spudders, in which case i could probably "turn out" some things that would be out of reach of most fellow members.
If it were up to me designing cannons though they would still have square wheels! My Apfsds rounds would be the bomb though!
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Unread postAuthor: mark.f » Thu Jan 31, 2008 7:05 am

MtCrowley wrote:Starting to get bored and thought I might make a hybrid to kick school of with a bang Smile

Anyway, just got a few Q's for the more knowledgeable.

I'm planning on shooting .177" metal BB's, projectiles around .3" and maybe 3/4" marble sized projectiles.

1) Chamber size, what sized chamber do you think I should go with for decent results. I was thinking maybe 9" of 1.25" steel pipe. Tad over-kill for the BB's but oh well.

2) Union, should I have multiple unions for each barrel, or just have one? If the latter option, what size should I make it?

3) I'll probably be using MAPP gas, would a spark plug with it's pre-set spark gap be fine for this? Or will I need to make the gap smaller?

4) Would tapping and epoxying a spark plug into the chamber be fine for mixes up to 6x? It's not going to be remote-ignition, so I just want to make sure.

5) I understand some have trouble getting burst disks to seal in their unions. I saw SB15's thread where he modded his, anyone else have their own way dealing with this problem?

Thanks, and yes SB15 it'll probably end up being similar to yours, the one many others have copied. :wink:


1.) That chamber size sounds fine. My First hybrid used a 5/4" SCH-80 seamless pipe nipple, and it provided plenty power for a 5' long ball-bearing barrel.

2.) I would suggest a 3/4" union. You can either get another union half for each barrel, or do what I do and just thread the different barrels into 3/4" bushings, and interchange with some wrenches and teflon tape.

3.) Most of the time, people don't worry about the addition of fuel and it's affect on the fuel mixtures density as compared to air. So, take the distance your ignition system can push a spark in open air, divide that by your planned mixture in atmospheres, (i.e. 4 for a 4x mix, 6 for a 6x mix), and that will be your maximum spark gap in that mixture, with a few percent error. If you're using a BBQ sparker, and a 6x max mix, going with about 1/2" gap in open air, that would give you a gap of 1/12" in compression. Most spark gaps are adjustable, so just get a gap setting tool and adjust to the correct width.

4.) I would tap it where a threaded coupler or cap overlapped the pipe, just because that's the way I done it on what I'm working on now. It may or may not be necessary, but that's also my suggestion.

Also, if you're copying SB15, why not use his Schrader spark plug idea? Or, if you want REALLY simple, PM me and I'll show you that way I interpretted "Schrader spark plug". :wink:

5.) The union thing is really problematic. DYI could help you all you want with this problem, because he helped me earlier this year trying to get a burst disk gun to seal.

Basically, what they did is grind down the tapered male sealing face on the "female" (expensive) half of the union, and installed a gasket. This prevented the foil disks from wrinkling, and let them seal at elevated pressures. I still have to do this to my cannon, which is the only thing I'm dreading.

Another REALLY simple way to solve it is to use rubber burst disks. Tire inner tube works great, but for elevated mixtures, you have to use multiple layers or you'll wind up with just a big balloon poking out your valve and rupturing on the breech. This seal regardless of union geometry.

6.) There is no #6. Good luck with building your hybrid, Crowley. What type of metering are you going to be using? SB15's air-through-the-meter setup is quite accurate, and would be the second system I would suggest, after a Gen. II system.
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Unread postAuthor: DYI » Thu Jan 31, 2008 2:19 pm

All your other questions have been answered quite well, and it doesn't look like SB15's got here yet, so here's my solution to the union problem:

Firstly, since only one side of the union will be pressurised, you may not even need to grind down the sealing face. Cut a gasket out of butyl rubber that fits the sealing face of the union and is a bit bigger on the inside than it needs to be. It'll take a bit of trimming to make sure it doesn't get chewed up in the union (which completely ruins it). I use gaskets on both sides of the union, to prevent the steel sealing face cutting into the alu. disk.

I only have experience with alu. foil disks, and the trick is to cut a rough outline, then press them onto the union. After that, turn them over and there will be a line right where the outer edge of the sealing face is. Cutting along that line will prevent them from ever jamming.

Make sure that the female tapered part of the union is the side that's holding pressure, because it usually seals better.

If it still doesn't seal, then grind down the male sealing face flat, but it shouldn't matter unless you're using sheet metal disks rather than foil.
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Unread postAuthor: MrCrowley » Thu Jan 31, 2008 3:01 pm

Thanks for that markfh11q and DYI.

@mark

With the schrader spark plug idea, I can't get any threaded schrader valves down here, and have used all the ones I got from America.
And I've got a bunch of spark plugs taking up space in my garage that need to be put to use. Thanks anyway.

Actually I did have a number #6, thought of it last night in bed, but as usual I've forgotten it :)

And yes, i'll probably go with SB15's metering setup.

@DYI

Okay thanks for that, if I ever have a problem with it sealing, these ideas seem logical to work.
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Unread postAuthor: mark.f » Fri Feb 01, 2008 7:03 am

MrCrowley wrote:With the schrader spark plug idea, I can't get any threaded schrader valves down here, and have used all the ones I got from America.
And I've got a bunch of spark plugs taking up space in my garage that need to be put to use. Thanks anyway.


Good thing you only need a rubber one for my idea. :wink:
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Unread postAuthor: Eddbot » Sat Feb 02, 2008 5:09 am

MrCrowley wrote:
Eddbot wrote:wow, are rugby championships the same time of year as american football superbowls, i'm assuming that joke was brought up because it has to do with current events in...New Zealand? i don't know what kiwi land is...


Rugby World Cups are during Winter, so depending on what country they are in, the month changes.

Yeah we lost to France in the Rugby World Cup, don't think we even got in the semi's and we're supposed to be the best team in the World.

Kiwi-Land = New Zealand. A Kiwi is a NZ flightless bird, and sometimes NZ'ers and referred to as Kiwi's.

Spose I gotta await for SB15 to get out of school so I can get some more advice :)


i'm sorry, i don't even like the sport, i just watch the superbowl for the commercials, plus, what the hell else am i supposed to call it "fake football"
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Unread postAuthor: MrCrowley » Sat Feb 02, 2008 5:15 am

Eddbot wrote:
MrCrowley wrote:
Eddbot wrote:wow, are rugby championships the same time of year as american football superbowls, i'm assuming that joke was brought up because it has to do with current events in...New Zealand? i don't know what kiwi land is...


Rugby World Cups are during Winter, so depending on what country they are in, the month changes.

Yeah we lost to France in the Rugby World Cup, don't think we even got in the semi's and we're supposed to be the best team in the World.

Kiwi-Land = New Zealand. A Kiwi is a NZ flightless bird, and sometimes NZ'ers and referred to as Kiwi's.

Spose I gotta await for SB15 to get out of school so I can get some more advice :)


i'm sorry, i don't even like the sport, i just watch the superbowl for the commercials, plus, what the hell else am i supposed to call it "fake football"


Sorry? I never questioned what you call American Football, please read your post so you are responding to the correct person.
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