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Hybrid build thread

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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Hybrid build thread

Unread postAuthor: Heimo » Tue Jun 22, 2010 3:28 pm

Greetings
I planned to build a hybrid for a few months now. My first Idea was to create a chamber out of cast Aluminum and I actually made one (the casting failed) anyhow today my dad rudely awakened me cause he wanted me go to the scrap yard with him, (the scrap yard is my favorite shopping store) anyhow I was looking for something completely different when I noticed some hydraulic actuators lying on a heap.
on closer inspection I found a small hydraulic actuator and then an Idea was born. For a mere $4.60 this beauty followed me home.
Sorry I forgot to take pics of me taking it apart

here is a pic showing the length of the chamber
the chamber is 180MM long

Image


Here you can see the ID of the chamber, it measures 40MM ID

Image

Here you can see the outer diameter it measures 75MM

Image

wall thickness is 17,5MM

Image

This is going to be a piston hybrid, I am still designing the piston valve I will definitely swing the Idea here before I make anything.

Will someone please calculate the burst pressure of this thing cause I don't have the faintest Idea how to do it myself, thank you in advance.

I am hoping that I will at least be able to take this thing to 25X

I will update this thread as things develop.

Heimo
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Unread postAuthor: SpudFarm » Tue Jun 22, 2010 3:35 pm

Nice find!

I won't get into piston hybrids since I have never made one but you can ask Galfisk.

This is probably very high grade steel, if the walls is as thick as they look like you should probably be fine up to sevral hundres-x as Larda crearly showed us.
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Unread postAuthor: Heimo » Mon Aug 30, 2010 4:48 pm

a small update: I have decided on a piston valve design and I have started construction I will attach a pic of the concept of the valve at the end.

Here is a pic of the rough valve body


Image

that is all you guy are getting from me tonight :D :D
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piston valve drawing.png
here is the concept drawing of the piston valve bear in mind that it is not drawn to scale and a lot of details may be omitted from the drawing..
piston valve drawing.png (30.45 KiB) Viewed 1119 times
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Unread postAuthor: kenbo0422 » Mon Aug 30, 2010 8:46 pm

Your pressure vessel looks to be thick enough to withstand 25x easily, if that is steel I'm looking at. Check it for cracks with a good magnifying lens.
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Unread postAuthor: Technician1002 » Mon Aug 30, 2010 9:15 pm

If the piston has equal pressure (multi X bar pressure) on both sides before firing, that will be fine by itself. The issue I see is the pilot vent will be unbalanced and may open the piston under pressure before firing.


A slight modification can make the pilot vent balanced too. Put the pilot vent port between the o rings and balance the pressure on the pilot vent. When fired, the main valve and pilot vent opens. Before firing, the piston and pilot vent are balanced.
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Unread postAuthor: SpudBlaster15 » Mon Aug 30, 2010 9:45 pm

While this valve will work, the design is very poor, to put it bluntly.

Your piston area ratio is actually lower than 1:1, which means that without 300PSI+ in the pilot chamber, your valve opening pressure will be far less than optimal for even low to moderate mixes.

I'm also very concerned with the cast aluminum valve body. Aluminum castings (Especially those done using a backyard foundry) are very prone to defects, namely trapped gas bubbles, and without proper heat treatment, aren't very strong to begin with. Which alloy did you use, and do you have any plans to artificially age harden it?
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Unread postAuthor: Technician1002 » Tue Aug 31, 2010 2:36 am

Just some quick input on Hybrid valves and 1:1 ratio. This isn't as critical as it seems. Due to the mass of the piston, the burn time of the mix, the distance the piston must move before the seal breaks at the port and o rings, the simple time delay of the valve mass may be enough to delay opening a decent burn.

What is the burn time vs opening time?
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Unread postAuthor: Crna Legija » Tue Aug 31, 2010 4:39 am

kenbo0422 wrote:Your pressure vessel looks to be thick enough to withstand 25x easily, if that is steel I'm looking at. Check it for cracks with a good magnifying lens.


It could take 70x easily if he makes the end cap and barrel holder strong enough, because its made for hydraulics they run at like 2,500psi+
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Unread postAuthor: spudtyrrant » Tue Aug 31, 2010 6:25 am

Technician1002 wrote:Just some quick input on Hybrid valves and 1:1 ratio. This isn't as critical as it seems. Due to the mass of the piston, the burn time of the mix, the distance the piston must move before the seal breaks at the port and o rings, the simple time delay of the valve mass may be enough to delay opening a decent burn.

What is the burn time vs opening time?
well for my hybrid hgdt predicts it will have burnt out at 14ms, by which time my valve would have been fully open for at least 8ms, so its a little more important than you might think.
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Unread postAuthor: Heimo » Tue Aug 31, 2010 7:52 am

Crap where to start??

Technician1002 wrote:If the piston has equal pressure (multi X bar pressure) on both sides before firing, that will be fine by itself. The issue I see is the pilot vent will be unbalanced and may open the piston under pressure before firing.


A slight modification can make the pilot vent balanced too. Put the pilot vent port between the o rings and balance the pressure on the pilot vent. When fired, the main valve and pilot vent opens. Before firing, the piston and pilot vent are balanced.


the way I planned it, it would have been an isolated pilot to allow me to control the opening pressure by controlling the pilot pressure.

to put the vent hole between the o rings to make it balanced sounds good to me, I will most likely incorporate this into the design. thanks for the advice


SpudBlaster15 wrote:While this valve will work, the design is very poor, to put it bluntly.

Your piston area ratio is actually lower than 1:1, which means that without 300PSI+ in the pilot chamber, your valve opening pressure will be far less than optimal for even low to moderate mixes.

I'm also very concerned with the cast aluminum valve body. Aluminum castings (Especially those done using a backyard foundry) are very prone to defects, namely trapped gas bubbles, and without proper heat treatment, aren't very strong to begin with. Which alloy did you use, and do you have any plans to artificially age harden it?


like I said I was planning this to be an isolated pilot design.

Yes Aluminum castings (Especially those done using a backyard foundry) are very prone to defects, but that is only because most backyard foundry men don't follow good foundry practice (and I do follow good foundry practice) 1 they don't control their furnace atmosphere and 2 they don't flux nor degas and to show you that this casting don't have absorbed hydrogen(the gas that causes gas bubbles in castings) I took a part of the gating system from this casting that you would most likely find bubbles if you got any absorbed gas, and I cut a section of it and polished it to some degree to show lack of bubbles

Image

as you can see there is no gas in this blind riser meaning it is nice and solid metal. the alloy used, I cannot remember the name of this alloy, but I can tell you that is a alloy that is a bit more malleable than most cast alloys. I am still looking into the artificial age hardening, still looking for a local place to get it done.

besides the most critical parts of this valve is going to be sleeved in seamless hydraulic tubing (shown on concept drawing)

-_- wrote:kenbo0422 wrote:
Your pressure vessel looks to be thick enough to withstand 25x easily, if that is steel I'm looking at. Check it for cracks with a good magnifying lens.


It could take 70x easily if he makes the end cap and barrel holder strong enough, because its made for hydraulics they run at like 2,500psi+


pic of the end cap of this chamber
Image

I also just got to add that the cast valve body is 16mm thick at the thinnest point
If you guys still feels that a cast valve body is unsafe or a bad idea, I'll skip the cast valve body and make this a burst disc cannon
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Unread postAuthor: kenbo0422 » Tue Aug 31, 2010 8:42 am

Even with no hardening, the thickness of your aluminum should be plenty. Max pressure under firing conditions shouldn't exceed about 500 psi and aluminum doesn't fail like PVC.
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Unread postAuthor: JDP12 » Tue Aug 31, 2010 9:42 am

kenbo... I dunno what mix your thinking of, but a higher mix hybrid (20x or up) is going to generate alot more pressure than 500psi
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Unread postAuthor: Heimo » Tue Aug 31, 2010 9:52 am

kenbo0422 wrote:Even with no hardening, the thickness of your aluminum should be plenty. Max pressure under firing conditions shouldn't exceed about 500 psi and aluminum doesn't fail like PVC.


the trouble is that I don't plan on firing this under 25X, only 25X and up to a max of 50X and HGDT gives me a prediction of 84 bar for a max chamber pressure (1 218 psi) so perhaps it would be a safer idea for me to first make a burst disc cannon out of this chamber and skip the cast aluminum on this for a while you guys made me doubt my aluminum casting :?
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Unread postAuthor: Dave_424 » Tue Aug 31, 2010 10:08 am

If I was you, I would just go with a burst disk design and use the steel chamber. It should be much quicker to build and allow the higher mixes that you were looking for.

Seeing as though the aluminium is the weak part, removing it from the mix will increase your maximum pressures.

I would say that, if there were no defects/cracks in the chamber and the end plates were over engineered enough, it would withstand 50x quite easily

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Unread postAuthor: kenbo0422 » Tue Aug 31, 2010 10:20 am

Touche.
Here is my version, using the same program (my mistake, 600 psi).
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HGDT info in mostly the same configuration, just a larger barrel and chamber opens right about the 25x pressure.
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