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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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Unread postAuthor: D_Hall » Fri Oct 14, 2011 8:13 am

Yes.

(And other words so the forum software doesn't complain about too short of a message.)
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Unread postAuthor: Moonbogg » Fri Oct 14, 2011 10:51 am

Do you feel inclined to share details on the piston design? Is it the check valve type or isolated pilot? Will the pilot exhaust upon firing? Barrel sealing or spool type with ports? I'm curious to see what type of valve you are confident in regarding reliability etc as I am working on one myself.
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Re: Pointers For a Newb Building a Hybrid

Unread postAuthor: SpudBlaster15 » Fri Oct 14, 2011 2:06 pm

03cumminsguy wrote:Pros and cons of Burst Disk vs. Piston


Burst disks are simpler, less expensive and better performing, but they can be time consuming to manufacture and swap out after each shot.

Piston valves are faster and easier to reset after each shot, and they do not require you to keep a supply of replacement disks on hand. However, they are generally more difficult and expensive to build, as well as slower opening.

I would definitely suggest a burst disk setup for your first hybrid.

Barrel connection? Camlock? any other ideas or options


Aluminum cam locks can be useful on hybrid launchers, but they are limited in application. If they are being used to hold a burst disk in place, I would not want to operate the launcher at higher than 5X or so, because the clamping mechanism isn't well suited for heavy loading along the longitudinal axis of the assembly. If the cam locks are simply being used to breech load and are not required to withstand extreme stress, they are usable at much higher pressures.

If you're planning to use a burst disk configuration, I would definitely use a modified union, as such a setup will be capable of sealing much more effectively at higher pressures.

Metering techniques? Pros and cons of those?


Volumetric metering is superior for lower mixes and smaller chamber volumes, but manometric setups are simpler and easier to use when the mixes are sufficiently high for the partial pressure of the fuel gas to be accurately measured prior to adding the oxidizer.
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Unread postAuthor: D_Hall » Fri Oct 14, 2011 2:25 pm

Moonbogg wrote:Do you feel inclined to share details on the piston design? Is it the check valve type or isolated pilot? Will the pilot exhaust upon firing? Barrel sealing or spool type with ports?

Granted, I've not followed all the piston valve hybrid designs so it may or may not have much in common (ex: not sure what you mean by a 'check valve type'). That said...

The pilot will exhaust on firing. I'm not 100% sure how well it will work, but the overall design of the gun is such that it should allow me to quickly/easily rework the design. So if it doesn't work 100%, I can address that later.

I'm curious to see what type of valve you are confident in regarding reliability etc as I am working on one myself.

Pretty standard piston stuff, really. But rather than spend a lot of time coming up with an exotic piston, I'm spending a bit of time coming up with a robust/effective bumper. At least, I hope I am. :D
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Unread postAuthor: Moonbogg » Fri Oct 14, 2011 6:05 pm

Yes, the bumper is a huge deal I agree. Good luck and I look forward to your cannon's progress.
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Unread postAuthor: 03cumminsguy » Fri Oct 14, 2011 7:09 pm

Thanks again for all of you guys help.

As far as the modified union goes. What parts are involved in that setup. And whats the difference between the two metering systems. I was planning on using ratcalc and fuel tool to help set up my metering.
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Unread postAuthor: MrCrowley » Fri Oct 14, 2011 7:22 pm

As far as the modified union goes. What parts are involved in that setup

In this photo, the union half on the left usually has a tapered lip protruding out from it, if you use an angle grinder to grind down the lip so the union face is flat, it is much easier to get the union to seal. If you do this modification, it helps if you have this modified half attached to the barrel as it provides more surface area for the disk to be forced against.

The second 'modification' involves getting some rubber gaskets or o-rings and using them on the 'chamber side' of the union between the union face and the burst disk to get it to seal under pressure.

And whats the difference between the two metering systems

Volumetric metering involves making a small 'fuel meter' that can be shut off from the main chamber. The volume of the fuel meter is calculated and then you pressurize it with your fuel of choice to a pre-calculated pressure. That pre-calculated pressure of fuel in the meter is the exact amount needed for a particular mix once the fuel meter is 'dumped' in to the chamber.

Manometric metering involves fuelling directly in to the chamber. You may have a manifold of gauges and valves, that can be shut-off from the chamber, that aid you in fuelling the chamber. On my manometric meter, I fuel directly in to the chamber and a 0-15PSI gauge that can be detached from the chamber tells me how much fuel I'm putting in.

I'm not very good at describing the methods as I do so in layman's terms, perhaps SB15 or another member can better describe the chemistry behind both types of metering.

Read this also:
http://www.spudfiles.com/forums/hybrid- ... 13602.html
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Unread postAuthor: 03cumminsguy » Fri Oct 14, 2011 7:33 pm

Thanks. So the 2 piece metal with nut is literally called a union? I am trying to find parts on line and as you could imagine metal union showed a bunch of people in black clothing and random metal band names. lol
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Unread postAuthor: saefroch » Fri Oct 14, 2011 7:41 pm

A better search term is "stainless steel union," or some other metal name. Try that.
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Unread postAuthor: 03cumminsguy » Sat Oct 15, 2011 12:54 am

Got another question for the spudding gurus. With a metal chamber. Wouldn't an electric igniter/stun gun arc to the barrel in turn shocking the unlucky holder of said cannon.
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Unread postAuthor: Technician1002 » Sat Oct 15, 2011 1:15 am

03cumminsguy wrote:Got another question for the spudding gurus. With a metal chamber. Wouldn't an electric igniter/stun gun arc to the barrel in turn shocking the unlucky holder of said cannon.


This shocks about the same as your car when the spark plugs spark from the center electrode to the side electrode and the metal engine block..

If you are not part of the current path, there is no problems. Same applies to your lawn mower and weed eater.

Be sure the ground lead of the spark source is connected to the metal chamber, or you can become part of the current path. That will get your attention if you do it wrong. :shock:
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Unread postAuthor: 03cumminsguy » Sat Oct 15, 2011 10:26 am

So i could run two bolts through the side of the chamber like in an advanced combustion set up and be fine?
To clarify on my over and under statement I made earlier. I meant run the chamber under the barrel not just the fueling system.
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Unread postAuthor: Crna Legija » Sat Oct 15, 2011 10:38 am

I don't think so, most people make spark plugs in a threaded cap, i would drill tap the chamber for 1/8'' npt and put a CR10EK spark plug in there, the threads on that plug are very close to 1/8''npt but not perfect a bit of epoxy will make it air tight.
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Unread postAuthor: 03cumminsguy » Sat Oct 15, 2011 4:03 pm

for running a spark plug set up. would you use a grill igniter and wire it to the plug?
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Unread postAuthor: MrCrowley » Sat Oct 15, 2011 4:08 pm

Yes, or any number of other igniters.

We do have a Hybrid Showcase section with a little over one hundred examples to study that can answer questions like these :wink:

A search of "spark plug" using "search for all terms" in the "Hybrid Cannon Showcase" section will return some relevant results for you to look at.
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