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Harness the power of precision mixtures of pressurized flammable vapor. Safety first! These are advanced potato guns - not for the beginner.
90zimara
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Mon Feb 08, 2021 11:25 pm

Hello everybody.

So, I created an account on this forum and made a similar post 3 years ago and had a lot of replies from this community, thanks by the way, unfortunately I had to stop due to things that got out of my hands. But now, 3 years later I am planning on using the power of hybrid cannons as a project for my thermodynamics class and pretend to be doing a lot of tests on it.

Unfortunately, I know the basics of a hybrid gun and how it works but I might need some help when actually building one. Scrolling through this forum I managed to encounter a build that might be capable of holding what my tests are going to be doing and seems to be made out of parts that I can easily obtain.

viewtopic.php?f=28&t=23605

This is the build, I just want to know like, how do I fuel it up, maybe on which parts should I get (I got a list of some parts that I managed to see on the pictures but might be missing some things.

I also can not attend DMs as it says that my account hasn't been properly active for that, sorry for the people that DM'ed me back in 2018.

Thanks.
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jackssmirkingrevenge
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Tue Feb 09, 2021 6:24 am

90zimara wrote:
Mon Feb 08, 2021 11:25 pm
I am planning on using the power of hybrid cannons as a project for my thermodynamics class and pretend to be doing a lot of tests on it.
Always the best excuse :)

I think you can go a lot simpler by just using a burst disk and fuel by volume (with a syringe) instead of by pressure.

Example of a burst disk hybrid made without sophisticated parts: viewtopic.php?f=28&t=21655

Fuel metering by volume: viewtopic.php?f=27&t=22301
hectmarr wrote:You have to make many weapons, because this field is long and short life
90zimara
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Tue Feb 09, 2021 6:59 am

jackssmirkingrevenge wrote:
Tue Feb 09, 2021 6:24 am
90zimara wrote:
Mon Feb 08, 2021 11:25 pm
I am planning on using the power of hybrid cannons as a project for my thermodynamics class and pretend to be doing a lot of tests on it.
Always the best excuse :)

I think you can go a lot simpler by just using a burst disk and fuel by volume (with a syringe) instead of by pressure.

Example of a burst disk hybrid made without sophisticated parts: viewtopic.php?f=28&t=21655

Fuel metering by volume: viewtopic.php?f=27&t=22301
I mean, I do actually pretend to go up to 6x, maybe 8x and pretend on use different types of fuel. I can show you the introduction to the paper if you want, just to let you know what I am looking for.
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Tue Feb 09, 2021 11:23 am

Second here for using a burst disk and syringe metering. In terms of complexity, the next step up from that would probably be manometric (using chamber pressure to measure fuel and air) fueling. The type of fueling SB15 uses on his cannons is volumetric ("air through meter" design which is pretty accurate though).

The valve on the TBMA requires building a completely-sealed spool as well.
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Tue Feb 09, 2021 12:25 pm

mark.f wrote:
Tue Feb 09, 2021 11:23 am
Second here for using a burst disk and syringe metering. In terms of complexity, the next step up from that would probably be manometric (using chamber pressure to measure fuel and air) fueling. The type of fueling SB15 uses on his cannons is volumetric ("air through meter" design which is pretty accurate though).

The valve on the TBMA requires building a completely-sealed spool as well.
How much pressure do you think I would be able to get by using syringes?

I also have some handmade pistons that I made back 3 years ago when I first started making my first cannon. It is somewhat similar to the post I linked, the dimensions may be different tho.
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hectmarr
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Tue Feb 09, 2021 6:46 pm

I agree with what they tell you. For your first hybrid barrel a rupture disc system is the simplest thing to do and is VERY EFFECTIVE! :evil:
You have to draw a picture of what you have in mind, hybrid barrel size, projectile type, fill pressure and all that. On the other hand, list your specific doubts, to be able to guide you on all this. Waiting for your ideas and doubts. :)
Check out this old project, a small handgun. What I want to show you is how simple it is to dose the fuel with a syringe., In this case the amount of air is defined by the amount of pumping, it is for this reason that you do not see any pressure(although this system does not use rupture disc) gauge. The amount of gas is defined by the volume of the syringe between the piston and the outlet hole.
First the fact and then the law.
90zimara
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Wed Feb 10, 2021 12:09 am

hectmarr wrote:
Tue Feb 09, 2021 6:46 pm
I agree with what they tell you. For your first hybrid barrel a rupture disc system is the simplest thing to do and is VERY EFFECTIVE! :evil:
You have to draw a picture of what you have in mind, hybrid barrel size, projectile type, fill pressure and all that. On the other hand, list your specific doubts, to be able to guide you on all this. Waiting for your ideas and doubts. :)
Check out this old project, a small handgun. What I want to show you is how simple it is to dose the fuel with a syringe., In this case the amount of air is defined by the amount of pumping, it is for this reason that you do not see any pressure(although this system does not use rupture disc) gauge. The amount of gas is defined by the volume of the syringe between the piston and the outlet hole.

I basically just have questions regarding how this one is fueled. I know how everything else works and I have a kind of prototype which I am trying to create on Solidworks before asking questions about the design. My only question right now is how the fueling system works on this one as it seems to be pretty simple and my cannon looks somewhat similar to this (in terms of size).
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hectmarr
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Wed Feb 10, 2021 2:25 pm

Simple.
In my case, (this is independent of the mixture retention system that the hybrid has, rupture disc, piston with pilot, o'ring only), for a given combustion chamber volume, I measured with my pressure gauge that with 6 pumps, I have 5 bar. As long as you give 6 pumps you will have 5 bar ...
Since I know that my combustion chamber is 20 cm3, I can deduce that at 6 bar I will have 120 cm3 of air.
The stoichiometric ratio of butane and air is between 3 and 8%, I use 5%. For 120 cm3 of air, you need 6 cm3 of butane. When I fill the syringe with gas, I fill it up to the 6 cm3 mark, and that's what you see that I inject directly into the combustion chamber, and then the 6 pumps of air. 8-)
First the fact and then the law.
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Wed Feb 10, 2021 5:41 pm

hectmarr wrote:
Wed Feb 10, 2021 2:25 pm
Simple.
In my case, (this is independent of the mixture retention system that the hybrid has, rupture disc, piston with pilot, o'ring only), for a given combustion chamber volume, I measured with my pressure gauge that with 6 pumps, I have 5 bar. As long as you give 6 pumps you will have 5 bar ...
Since I know that my combustion chamber is 20 cm3, I can deduce that at 6 bar I will have 120 cm3 of air.
The stoichiometric ratio of butane and air is between 3 and 8%, I use 5%. For 120 cm3 of air, you need 6 cm3 of butane. When I fill the syringe with gas, I fill it up to the 6 cm3 mark, and that's what you see that I inject directly into the combustion chamber, and then the 6 pumps of air. 8-)
Will the fueling method of syringe work for up to 6x or maybe 8x?
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hectmarr
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Wed Feb 10, 2021 5:58 pm

Yes! If the amount of gas exceeds what your syringe can hold, get yourself a bigger one, or make one the size you need, with recycled materials.
Example:
If in the gun in the video I use 30 bar, the amount of air is 30 times 20 cm3, (which is the volume of my combustion chamber), about 600 cm3 of air. If the gas ratio is 5%, you need 30 cm3. A syringe for veterinary use is normally about 70 cm3.
Of course, these numbers are just an example, because if I give 30X to this old thing, the weapon in the video, my head can be in orbit and my mother-in-law will throw a party, film it and upload it to YouTube! :o :)
First the fact and then the law.
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Wed Feb 10, 2021 11:23 pm

90zimara wrote:
Wed Feb 10, 2021 5:41 pm
Will the fueling method of syringe work for up to 6x or maybe 8x?
The biggest syringe that is easy to get is 70ml. If you fuel into a vented chamber you are probably limited to putting in no more than about 20% of the chamber volume. After that you'll be losing an unknown amount of fuel as it leaks and vents. Assuming propane, 20% would be 5X (1X=4%). 70ml is 20% of 350ml.

If you fuel into a closed chamber, for example through a schrader valve, then you are limited by how hard you can push on the syringe, which is part of the reason people go to a meter pipe, valves and a regulator for mixes above 5X or so.
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Thu Feb 11, 2021 6:12 am

I also have another question, I once read on this forum that the best ratio between Chamber and Barrel is 1:1 but then I also read somewhere else it was around 3:1, now, I know there is a software but it seems loke the original link is broken and I can't get a hand on it :/ I also haven't done any models and prototypes as I want to see what materials I can find where I live (small town in Colombia).
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Fri Feb 12, 2021 5:10 pm

"best ratio" is not a well defined concept. Do you mean "most efficient" at extracting the energy in the explosion, or "fastest projectile" but that requires knowledge of projectile and barrel ... Long story short for 1X mixtures CB ratios between 0.6 and 1.2 are all about the same. Let other factors make the final decision.
spud_wiki/index.php?title=Chamber_to_barrel_ratio

I think the software you mention is probably GGDT (gas gun design tool) for pneumatics or HGDT (hybrid gun design tool) for combustion guns. Both were written by D. Hall. The spud gun wiki page's link appear to be dead.
I think there are links here in the forum, try: https://spudfiles.com/viewtopic.php?p=387228

I just downloaded the HDGT.zip file, unpacked it and hgdt.exe runs on my windows 10 machine.
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Fri Feb 12, 2021 6:45 pm

Look at this, it can illustrate for you how to work with rupture disc.
First the fact and then the law.
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Fri Feb 19, 2021 4:35 pm

hectmarr wrote:
Fri Feb 12, 2021 6:45 pm
Look at this, it can illustrate for you how to work with rupture disc.
LOL, looks like the fittings salesman's wet dream.
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