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?s with biohazard.

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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Re: ?s with biohazard.

Unread postAuthor: D_Hall » Tue May 06, 2008 6:38 pm

pat123 wrote:3. does anyone haave a really accurate way to measure the volume? Drex was talking about pouring water in with a measured container but I don't want to fill a 600ci chamber with water cup by cup.

If you have a decent scale, weight it empty and full (of water).
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Unread postAuthor: DYI » Tue May 06, 2008 7:14 pm

Haven't you read my "Hybrid1" thread?

It isn't any secret, and it was developed long ago. I just call it mine because I was the first (that I know of) to actually get around to implementing it.

It will eventually be universal, but for now it's only capable of 1-20x air/propane, and 2-25x oxy/propane.

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Ports: Outlet, air, oxygen, propane, 0-300psig Grade 1A gauge, 0-15psig Grade 1A gauge.

In short, it measures chamber pressure developed by fueling, accurately enough that you can meter 1x mixes with it (0.6psi propane).
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Re: ?s with biohazard.

Unread postAuthor: Ragnarok » Tue May 06, 2008 7:17 pm

D_Hall wrote:If you have a decent scale, weight it empty and full (of water).

I do have doubts that many scales that could take the weight of a large hybrid full of water would have any precision beyond perhaps 0.2 kg jumps (which would be +/- 0.1 kg)

You might get lucky and find a 0.1 kg graduated one, but that's still quite a large amount of room for error.

There is however, no need to fill cup by cup. With a large funnel and a 1 litre jug, a hybrid of around 600 ci would only need 9 fills from a litre jug, and after that, you could switch to a smaller, more precise measures to do the remaining 800 cc or so.

Of course, I do seriously recommend DYI's metering system, as you have absolutely no requirement to measure chamber volumes.
The metering works by injecting a pressure, rather than a volume of propane - SpudBlaster did a very good write up of the maths involved.
You then top up to the full pre-ignition pressure with air.

DYI could take that meter, attach it to any hybrid in the world - from the monster D_Hall is designing, all the way down to Nova's Brass Bruiser - and without a single measurement (although perhaps a few button presses on a calculator), use it to accurately fill to up to 20x mixes.
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Unread postAuthor: Lentamentalisk » Tue May 06, 2008 7:22 pm

Granted it could take ages to fill one of the larger ones.
Though it could easily be adapted to have a larger metering pipe to fix that.
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Unread postAuthor: DYI » Tue May 06, 2008 7:33 pm

Granted it could take ages to fill one of the larger ones.
Though it could easily be adapted to have a larger metering pipe to fix that.


I don't think you quite understand yet; there is no metering pipe. You don't even need to inject the fuel through the meter. Take D_Hall's Pipe Dream for example: He could have the exact same fuel and oxidiser delivery systems (probably 2" hose or something :roll: ), tap a 1/4" hole on the other side of the thing, and plug this meter in, and it would work. I only inject through the meter because I'm not filling a gun the volume of a house, and I don't want 3 holes in the back plate when I could have 2.

I'm guessing that the reason nobody has built one of these before is that the gauges cost about $30 each. However, with a conventional system, the meter needs to be customised to the individual launcher, meaning a new meter for every hybrid.
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Unread postAuthor: Lentamentalisk » Tue May 06, 2008 7:41 pm

Ooooooooooooooohh I get it now! That is absolutely genius! I may just have to do that, though the gauges are rather expensive.
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Unread postAuthor: pat123 » Tue May 06, 2008 7:43 pm

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Unread postAuthor: Ragnarok » Tue May 06, 2008 7:43 pm

In a different way, I suppose you could think of the chamber as it's own metering pipe, and DYI's meter as just an advancement of the gauges people have on their external meters
...although it seems increasingly less common these days... but a good example is here on Latke's miniL1: http://www.burntlatke.com/jpg600/mini-side.jpg

Rather than filling a meter volume to a set pressure, you fill the chamber itself to a set pressure. It's simple, but ingenious - no conventional captive volume metering here.
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Unread postAuthor: drex » Tue May 06, 2008 7:44 pm

30 bucks sounds plenty reasonable seeing as you can reuse it on any future hybrids. i will definitely look further into your metering system.
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Unread postAuthor: pat123 » Tue May 06, 2008 7:50 pm

In a different way, I suppose you could think of the chamber as it's own metering pipe, and DYI's meter as just an advancement of the gauges people have on their external meters
...although it seems increasingly less common these days... but a good example is here on Latke's miniL1: http://www.burntlatke.com/jpg600/mini-side.jpg

Rather than filling a meter volume to a set pressure, you fill the chamber itself to a set pressure. It's simple, but ingenious - no conventional captive volume metering here.

I understand that but will the gauge I posted work?
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Unread postAuthor: DYI » Tue May 06, 2008 8:03 pm

The plumbing site has no mention of the gauge's accuracy, or even accuracy grade. If it's a "D" grade, it won't be accurate enough. I rarely ever make a purchase without all the information on a product, and this just seems like a bad idea.

On McMaster, all the relevant information is given, the selection is enormous, and the prices aren't very bad in most cases. I used 4053K16 from McMaster. The 1.5" and 2" face versions are GradeA (+/- 1% mid scale accuracy), and the 4" face version (the one I go) is Grade 1A (+/- 1% full scale accuracy). They're the best deal that I managed to find.
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Unread postAuthor: jimmy101 » Wed May 07, 2008 1:13 pm

The fuel ratio really isn't all that critical. It's not like 4% (final percentage) will ignite but 4.2% will not. Anything between about 3.8% and perhaps 6% is going to fire and will give basically the same performance. So, don't worry about figuring out your chamber volume to a high degree of accuracy. The only time you would need extremely high accuracy on the fueling would be if your burst disk is designed to rupure at very nearly the maximum chamber pressure.

More important is the not having any gross errors in your meter setup. Again, the actual accuracy of the meter doesn't have to be all that good but if you think your injecting, for example, 100cc but your are actually injecting 10cc then that's a problem. (DYI's method requires a fairly accurate, and reproducable gauge.)

A closed combustion chamber, at 1X, without a brust disk, makes almost zero noise when fired. If you are expecting a loud bang you might miss the faint noise created by combustion when the burst disk doesn't fail. As others have said though, how much noise it makes will probably depend on the details of the burst disk.

I would think you would be able to tell if the chamber fired just by the temperature rise. The temperature rise won't be much but I would think a hybrid would give enough of a rise that you could feel it with your hands.
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Unread postAuthor: SpudFarm » Wed May 07, 2008 2:52 pm

my small hybrid got quite hot at 5x.. i could feel it really good
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Unread postAuthor: pat123 » Wed May 07, 2008 2:54 pm

I may not have noticed it going off. it was a 1x mix and the walls on the tanks are like half and inch thick
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Unread postAuthor: SpudFarm » Wed May 07, 2008 2:57 pm

oh 1x.. go to 8x tomorrow.
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