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Pointers For a Newb Building a Hybrid

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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Pointers For a Newb Building a Hybrid

Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 12:44 am

I have played around with my basic combustion. Love the boom. I love the thought of basically having an explosion in my hands and sending a potato hurling through the air. I also love the Power of my pneumatic. The simplicity I have to change barrels and the simplicity of air and ammo. However, I am looking to make something new than I have previously and something with hopefully a little more "Bang for the buck"

In simpler words, I want to build a hybrid. I would love to have any and all input on this subject as well as any designs plans.

A few questions I do have that I wouldn't mind being answered:

Pros and cons of Burst Disk vs. Piston
Barrel connection? Camlock? any other ideas or options
Metering techniques? Pros and cons of those?

Thank you in advance
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Re: Pointers For a Newb Building a Hybrid

Unread postAuthor: jackssmirkingrevenge » Thu Oct 13, 2011 12:47 am

03cumminsguy wrote:A few questions I do have that I wouldn't mind being answered


A couple you should answer for more relevant answers:

- how big do you want to go, in terms of overall size and calibre?

- what sort of performance are you looking for?

- what sort of budget are you on?

- what materials and tools do you have available, and what's your experience with working with them?
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Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 1:01 am

I's like to shoot canned cola. So 2.75in barrel with chamber to fit. But the ability to downsize to say 1.5 for a golf ball.

As far as performance goes. I have nothing to prove so I believe a 10x mixture at tops would suffice. I have no need to put anything through a sheet of steel by any means.

Budget: if possible around or under $100. Not looking for a billet masterpiece. Just something to have some fun with.

Materials: not much laying around the house. A few odds and ends of pvc which I would prefer from what I've already researched not to use for the hybrid. Some copper pipe. But no elaborate selection.

Tools: Confidence with every tool I have at my dispense. Welder, Table saw, hacksaw, sawzall, drill press, screwdrivers, hammers, wrenches, I mean if there are other specific tools I may need tell me and Ill give a yay or nay.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 13, 2011 1:20 am

Ah, better :)

For such a large bore, I would eliminate a piston design as it would be far too large and certainly over budget.

On the simplest level, without pressurised fuel metering, rather using a syringe, I would go for a length of steel pipe blocked off at one end (threaded endcap or welded on if you have the facilities) - this end would be threaded for a small spark plug and schrader valve - and a 2" or 2.5" female camlock fitting on the other end.

As to ignition, a simple BBQ piezo is good for 15x at least with a small enough spark gap, but you might want to splash out on something more upmarket like a stungun or oven ignitior.

This assumes you don't want to have it with an on-board fuel supply and manometric metering, and just want a rudimentary setup that doesn't need to be hand held or look pretty.
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Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 11:36 am

I'd like to use on board propane with metering. Is there anything else you would suggest for that being said?
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 13, 2011 1:11 pm

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Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 1:47 pm

I like Spudblasters UPHL-158CI SB15's hybrid, a lot. Just the general design.

Also to be said is McCrowleys 1.5" porting handheld piston hybrid. I like the general size. And the m840s union setup.

I guess I'm just trying to make sure I have a good plan to begin with before screwing it up. I don't understand the concept of the piston. I get that it seals the barrel and creates two zones of pressure. The part I am unsure of is the combustion part. I totally understand the pneumatic side where the drop of the one side's pressure allows for the piston to move back releasing the pressure through the barrel. I don't understand how combustion fits into the equation as well as porting.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 13, 2011 2:04 pm

03cumminsguy wrote:I don't understand the concept of the piston. I get that it seals the barrel and creates two zones of pressure. The part I am unsure of is the combustion part. I totally understand the pneumatic side where the drop of the one side's pressure allows for the piston to move back releasing the pressure through the barrel. I don't understand how combustion fits into the equation as well as porting.


The combustion version is different from the pneumatic in that instead of lowering chamber pressure from the pilot side, it creates an imbalance by increasing pressure on the chamber side.

Effectively the combustion creates an overpressure and the piston acts like a pop-off valve, releasing the hot gasses through the barrel.
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Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 2:45 pm

For safety sake. Would you recommend just going with a burst disk setup? or is there another thread in your book about building pistons that you would recommend using for the setup I am trying to configure.
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Unread postAuthor: Labtecpower » Thu Oct 13, 2011 2:50 pm

A well built piston valve gun is just as safe as a well built burst disk gun.

I think a piston valved hybrid is even safer, because the pressure at wich it pops is more controlleable.
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Re: Pointers For a Newb Building a Hybrid

Unread postAuthor: MrCrowley » Thu Oct 13, 2011 3:07 pm

03cumminsguy wrote:Pros and cons of Burst Disk vs. Piston
Barrel connection? Camlock? any other ideas or options
Metering techniques? Pros and cons of those?

Burst Disk:

Pros:
Has the potential for more flow so you get better performance out of the valve.
Easy, simple, cheap.

Cons:
Requires a new disk to be loaded each shot.
Can sometimes be quite tricky to get the disk to seal, the use of o-rings or gaskets in conjunction with modifying the union may be necessary.
The disks are a pain in the ass to make. Making disks for 2" unions or larger would be quite annoying. If you're happy to dedicate a Sunday afternoon to cutting circular disks from soda cans, milk bottles, several dozen layers of tin foil or other suitable material, then go with a burst disk.
Burst disks can also be more difficult to 'fine tune' for each mix number. With a piston valve you can calculate roughly how much pressure you need in the pilot for a particular fuel mix so that the piston will be forced open upon combustion.


Piston Valves:

Pros:
Potential for a higher rate of fire
Performance is still pretty good but not as good as burst disks
Easy to fine tune for each fuel mix
No disk cutting

Cons:
Probably more expensive to make
Much harder to make as making the piston requires a decent amount of experience so you can easily troubleshoot the problems you will undoubtedly run in to
Can be destroyed by the combustion pressures fairly easily. It's taken me about 9 months to finally make a piston that doesn't wear out after a dozen shots.
More things to go wrong, if an o-ring is buggered or a leak appears you can't fix the problem in the field.


I'm sure there's more that I missed.
In short, if you have no problem making disks for the union, go with a union. For a 3/4" union and a 10x mix, I use 64 layers of aluminium foil. DYI would be able to tell you how many you need for a 2" union but all I can say is that it would be more than 64 layers and you'd cut a much larger disk.

If you can afford it, go with a 2.5" or 3" valve.

You could use a camlock for the barrel, it is a bit dodgy as the aluminium ones aren't rated very high but I believe SpudBlaster15 has used them on his hybrids. If you're planning on changing the barrels in the field, it might be easier going with a camlock connection although if you don't, you only have to bring a plumbing wrench with you to change the barrel.

For fuelling, I recommend manometric metering. Some will agree with me, others might disagree. I've used volumetric and manometric in the past and I much prefer the latter. I've got consistent results every time and I find it much easier and quicker to fuel. Manometric metering will require a fairly accurate (1% F.S. would be ideal) pressure gauge that reads no more than 15PSI.
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Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 3:19 pm

What do you mean? What valve are you talking about? Sorry I'm not following this.[/quote]
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Unread postAuthor: MrCrowley » Thu Oct 13, 2011 3:20 pm

What part of my post are you referring to?

I talked about two valves, piston and burst disk.

Edit:
Are you confused by the union? That's what a burst disk uses by the way.
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Unread postAuthor: 03cumminsguy » Thu Oct 13, 2011 3:46 pm

Just where you said "If you can afford it, go with a 2.5" or 3" valve." What valve are you talking about?
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Unread postAuthor: MrCrowley » Thu Oct 13, 2011 3:46 pm

Either piston or burst disk.
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