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Short question topic

A place to ask general spud cannon related questions.
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Re: Short question topic

Unread postAuthor: hectmarr » Sat Sep 28, 2019 10:02 am

mrfoo wrote:If you're playing at 12 meters, 1 arc minute (one click) is equivalent to 3.5mm.

Comes from trigonometry. SOH CAH TOA ,if you remember your schoolin'. For a right angled triangle, the tangent of one of the non-right angles is equal to the length of the side opposite that angle divided by the adjacent side. One arc-minute is equal to 1/60 degree (and an arc-second is equal to 1/60 arc-minute).

tan (1 / 60) = offset / distance to target

thus

offset = distance to target * tan (1/60)

Obviously, you need to choose units to fit the likely offset, which will mean upscaling your distance to target - 12m = 12000mm.

Yes, you are absolutely right. I was watching on youtube about this, and my understanding is clearer. I think it will be enough for what I need. 8)
I understand that this type of gun pointer works just like a laser that really illuminates the target. The difference is that this point APPEARS to be in the objective. Visually, for the eye, it is the same. Of course, at 50 meters, as an example, a point of light on a target is more difficult to see, if it is under the sun, much more, an issue that does not happen with a reflex sight, because the red or green point is very close Of the eye, and isolated from the strong exterior light by the viewfinder tube.
 
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Re: Short question topic

Unread postAuthor: Cthulhu » Tue Oct 01, 2019 4:58 pm

Can someone explain manometric metering for me? I tried to read the wiki and I understand you are filling a chamber to a set pressure with fuel then compressing the chamber with the correct pressure of air for combustion, but is it just composed of a simple pressure gauge and a single ball valve?
It's calculated with simple PV=nRT as well right?
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Re: Short question topic

Unread postAuthor: hectmarr » Tue Oct 01, 2019 6:26 pm

Cthulhu wrote:Can someone explain manometric metering for me? I tried to read the wiki and I understand you are filling a chamber to a set pressure with fuel then compressing the chamber with the correct pressure of air for combustion, but is it just composed of a simple pressure gauge and a single ball valve?
It's calculated with simple PV=nRT as well right?

I think you mean the manometric pressure measurement?
This measurement, takes as zero the atmospheric pressure existing at the time of measurement, something like relative pressure.
The absolute pressure includes the pressure measured with a pressure gauge, plus the atmospheric pressure.
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Re: Short question topic

Unread postAuthor: Moonbogg » Tue Oct 01, 2019 6:49 pm

I think it's only good for higher mixes because the post fuel chamber pressure is really low for anything below 10X really. Also, I'm pretty sure you can use HGDT for the post fuel chamber pressure if you want.
As for how to get the fuel in there, I don't know. Schrader valve maybe or quick disconnect?
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Re: Short question topic

Unread postAuthor: Cthulhu » Tue Oct 01, 2019 11:07 pm

If it's only good for higher mixes then I guess it won't be much use for me :lol:
I know syringe fueling can be used for hybrids. but could a homemade pump with the inlet port attached to a balloon filled with propane-air mix from a torch nozzle be used?
primitive fuel meter.jpg

I know it's primitive but I think it would be easier to just inflate a balloon and pump it into the chamber instead of having to measure fuel and pressure between each shot.
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Re: Short question topic

Unread postAuthor: mrfoo » Tue Oct 01, 2019 11:57 pm

Probably, but I'm not sure how you're proposing to guarantee a stoichiometric mix from a propane-oxygen torch. All the ones I've seen have 2 pressure regulators, and a torch with 2 controls, it's no just a "press the button for perfect mix" type setup.
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Re: Short question topic

Unread postAuthor: Moonbogg » Wed Oct 02, 2019 1:23 am

Personally I don't like having fuel mixed with oxygen until it's inside my chamber. It's just a thing with me I guess.
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Re: Short question topic

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Re: Short question topic

Unread postAuthor: hectmarr » Wed Oct 02, 2019 7:37 am

I misunderstood your question!
If you get a simple air pump, with an intake valve, when the pump tries to suck air, it can suck the combustible gas and then air only until it reaches the required pressure.
Another option is to inject the propane dose directly into the combustion chamber with a syringe and then refill with air ... Le muestro un video y un dibujo.
When you press the valve that lets the gas from the tank, "A", the air from the dispenser is expelled and is filled with butane, it is a volumetric meter. Hole "B" lets out a little to maintain atmospheric pressure.
When the pump aspirates for "C", it sucks the butane gas (the first pump), and then only air, (also for "B"), until it reaches the necessary pressure that you have programmed. The air pump pre mixes the gas and air. My autonomous hybrids 1, 2, 3 and 4, work this way. :shock:
This method, that of drawing, allows you to use small things, (a balloon is very large and unsightly), and not having mixed air and fuel, because it is dangerous.
This is what the actual installation of what I have drawn looks like.

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Re: Short question topic

Unread postAuthor: Cthulhu » Wed Oct 02, 2019 3:12 pm

That's a good idea hectmarr, I might need to look into making something like that.

mrfoo wrote:Probably, but I'm not sure how you're proposing to guarantee a stoichiometric mix from a propane-oxygen torch. All the ones I've seen have 2 pressure regulators, and a torch with 2 controls, it's no just a "press the button for perfect mix" type setup.

I'm probably wrong, but don't those cheapo bernzomatic torches use the venturi effect in their nozzle which pulls in air behind the fuel right at the nozzle to mix in the right amount of air?
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Re: Short question topic

Unread postAuthor: mrfoo » Wed Oct 02, 2019 11:53 pm

> venturi effect

Yep, but that requires there to be atmospheric pressure on both sides. If you try using one to push an air-fuel mix (which is, in passing, a very different animal to an oxy-fuel mix) into a pressurised container, it simply won't work.
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Re: Short question topic

Unread postAuthor: Cthulhu » Thu Oct 03, 2019 12:36 am

mrfoo wrote:> venturi effect

Yep, but that requires there to be atmospheric pressure on both sides. If you try using one to push an air-fuel mix (which is, in passing, a very different animal to an oxy-fuel mix) into a pressurised container, it simply won't work.


oh that makes sense, so it might not work even with the flexible container of the balloon.
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Re: Short question topic

Unread postAuthor: Moonbogg » Thu Oct 03, 2019 2:05 am

mrfoo wrote:> venturi effect

Yep, but that requires there to be atmospheric pressure on both sides. If you try using one to push an air-fuel mix (which is, in passing, a very different animal to an oxy-fuel mix) into a pressurised container, it simply won't work.


There's a guy on youtube that had a video with a spud gun that worked like that. Well, the thing worked like 1 try out of 10 because it was completely starved of oxygen and he appeared to have absolutely no idea why it wasn't working. It was really frustrating to watch a cannon get butchered like that, lol.

Oh look, here it is.

https://www.youtube.com/watch?v=vW4F5NB7Tsk&t=706s
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Re: Short question topic

Unread postAuthor: hectmarr » Thu Oct 03, 2019 7:21 am

You can try to use this type of blender mixer by first filling a "loading chamber" at atmospheric pressure so that the venturi effect can work, then closing this "loading chamber" and only then, from here, pumping under pressure Inside the gun's combustion chamber ... I don't know, I haven't tried this, it's just an idea. The problem is that the chamber that must be filled with the mixture first, must be quite bulky, precisely because it is filled with fuel-air mixture, at atmospheric pressure. :wink:

I really like this cannon!
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Re: Short question topic

Unread postAuthor: Moonbogg » Thu Oct 03, 2019 9:15 am

Yes, it looks good and is a nice size. I don't think they realized how powerful it could have been with a proper fuel mix.
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Re: Short question topic

Unread postAuthor: hectmarr » Mon Oct 07, 2019 9:32 am

This system, that of the video canon, is good for weapons without prior compression, that is, combustion weapons. What needs to be done is to incorporate a two-way valve, in the combustion chamber, so that the air comes out while the mixture dosed by the venturi of the welder enters. Then you close the valve and it should work well if the mixture is correct. The cleaning of burnt gases occurs when this gaseous residue is displaced by the mixture that enters, although it would be wasted a little. The inlet and outlet should be positioned in a way that facilitates the scanning of burnt gases.
You could use something like this for a small weapon, maybe :roll:
In the video, the gun explodes when he wants for this reason. After exploding once, it is full of burnt gases. When the boy tries to repeat the explosion, it does not happen until the burned gases are expelled by the mixture that enters ,, (in two or three attempts). Only when it is clean and there is only mixing, you can shoot again. 8)
 
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