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New to hybrids

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: New to hybrids

Unread postAuthor: Juggernaut12121 » Tue Aug 19, 2014 3:28 pm

I need some help with my first hybrid. I cannot, for the life of me, get this union to seal. I used a dremel to grind it down, a file to even it out, and a sander to smooth it out. I then cut up a thick rubber washer to use as the gasket. When I tested it with aluminum foil and cans, it leaked quite a bit. Sometimes subtly and sometimes just hissed but usually the same amount. I've spent an hour and a half modifying the union and then over an hour trying different things to get it to freaking seal. But to no avail :(
Any suggestions?

UPDATE: Alright, I feel really stupid XD
When I built it I hadn't realized the union setup was apparently backwards, and after I had it all done I did but was too lazy to take it back apart and fix it, thinking that it should work either way, I just tried it with the union the other way around
and it still leaks pressure but much more slowly, I think I just have to re seal the threads on it and it should be fine
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Re: New to hybrids

Unread postAuthor: MrCrowley » Tue Aug 19, 2014 4:27 pm

It can be quite difficult to find a setup that works consistently. You want the flat part of the union (probably the piece you modified, in the middle in the pic below) on the barrel. The reasoning here is that you want the most surface area for the disks to be pushed against. This prevents them slipping out prematurely (they'll crumple rather than burst) and helps with sealing. Now the union piece attached to the chamber (left in the pic below) doesn't usually have as nice a surface for sealing disks because it often consists of only a flat thin ring around the circumference of the fitting. Several gaskets can be used in conjunction with each other here to create a seal between the disks and chamber union fitting. However, I find that gaskets deform easily from both the heat and metal burst disks shredding.

The best solution I found, which I still use, is to layer the inside of the chamber union fitting (left below) with o-rings of various sizes. You want enough o-rings to be level with the surface of the fitting and then add one more, which will extend out of the fitting, when you put the burst disks in.

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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Thu Aug 21, 2014 8:21 am

My gasket has held up thus far, and hopefully for a while more. If it fails then I've got plenty of extra O-rings to try that out ^.
Another random question, this time about circuitry (where I'm even more of a noob), say I'm trying to make an ignition circuit, and I have a 12volt power supply (stemming off to two switches, one remote and one momentary), how would I get a spark to arc across a sparkplug from there? I thought I would need to get/build a step up transformer between the switch and the plug, but I'm not entirely sure if that was all I had to do. And if that is all I have to use then where can I find a transformer of decent output (enough to easily ignite a 10x mix)? Correct me if I'm wrong but it Mr.Crowley, you have a 30kV one right? I seem to recall that you had a little bit of trouble igniting 10x mixes?
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Re: New to hybrids

Unread postAuthor: MrCrowley » Thu Aug 21, 2014 12:53 pm

Yeah you're gonna need some form of sparker or another. I don't think the problem with my one is the 30kV as you can get sparkers with a lower output voltage that work just fine. Currently, I'm looking in to whether it is the batteries that are causing the problem.

Anyway, grab one of these:
offtopic-related/topic25951.html#p377495

Someone else was looking for a stungun replacement and found a cheap sparker on eBay. I bought one myself, it arrived yesterday, and sparks pretty well. Haven't tested it on a hybrid yet but I'd be confident it'd work.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Thu Aug 21, 2014 4:35 pm

Thanks! I meant to say that the step up transformer would act as my sparker. I just wasn't sure if there was much more to the circuit or if it was just that.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Sun Sep 07, 2014 8:05 am

Alright, being a noob I find that I can generate stupid questions pretty easily :P
Regarding a piston hybrid, is there any reason to totally ditch the idea of having a solid aluminum piston? It would be heavier and thus put more stress on the launcher, but would it really be enough to consider not doing it? I figure a solid one would give better performance since it only has a small area for the chamber pressure to work on, so the chamber needs to reach a higher pressure to push it back.
And what do you hybrid users prefer, shoulder fired or hip fired? I'm starting to design one (I'll might make some sort of build log when I know exactly what I want to make) and I ran into this problem, I'm not sure which way I'd like better so it'd help to hear some opinions. I forgot what other question I had :?
A big thanks in advance!
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Re: New to hybrids

Unread postAuthor: MrCrowley » Sun Sep 07, 2014 3:59 pm

is there any reason to totally ditch the idea of having a solid aluminum piston?

As you say, weight. I would've done it myself if I were getting it machined professionally but a kind SF member did it for me instead so I thought I'd keep it simple.

I figure a solid one would give better performance since it only has a small area for the chamber pressure to work on, so the chamber needs to reach a higher pressure to push it back

Force would be the same between a solid and a weight-reduced piston. The increased surface area is cancelled out by an increased surface area in the opposite direction. The force pushing on the face of the piston, around where it seals against the barrel, is still only what matters.

And what do you hybrid users prefer, shoulder fired or hip fired?

Hip fired. I know SB15 shoulder fires his but it seems much less comfortable and accurate that way, perhaps not as I've never tried it myself. Without that cross-bar on my cannon, though, it freakin' hurt to hip fire but I doubt shoulder firing would be any better. Not that it really matters, but I prefer not having a hybrid right next to my head either :wink:

edit: hybrids can be a bit difficult to control without a good grip...
https://www.youtube.com/watch?v=mXnopYJQh_s
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Re: New to hybrids

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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Sun Sep 07, 2014 7:34 pm

MrCrowley wrote:edit: hybrids can be a bit difficult to control without a good grip...
https://www.youtube.com/watch?v=mXnopYJQh_s

"Holy fuckin..."
"That hurt..." XD XD

I totally forgot about the pressure hitting the other side of the sealing face, thanks!
I'll probably aim to hip fire mine, I don't quite like having the piston slamming right next to my face and the pilot exhausting right behind it. That being said I'm not too sure how to get a good enough grip on the thing. I'll have to play with it some more
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Re: New to hybrids

Unread postAuthor: MrCrowley » Sun Sep 07, 2014 8:00 pm

Well what I did was to just install a 1"x12" long galv. tube perpendicular to the length of the chamber. Until recently, it still consisted part of the chamber volume (even though some expressed doubts as it may cause issues with fuel mixture) but now I have blocked it off with epoxy.

Anyway, it was just a piece of pipe that went across the front of my abdomen to help spread the recoil out over a large surface area. It also helped with grip too, before I had almost dropped the cannon several times when firing it. It's a simple solution, and one that I'd recommend. Have never had an issue with recoil since.

By the way, do you think you would benefit from a video explaining how to calculate the forces in a hybrid piston? I've thought about doing one for my youtube channel to help explain how a piston hybrid words as I think people are still confused about having pilot air pressure separate, and at a high pressure, to the chamber pre-ignition pressure.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Mon Sep 08, 2014 5:34 am

I believe I have the concepts all down pretty well, with the pilot exerting such a force of the larger surface area on the back of the piston and then the chamber having to go up to a higher pressure than the pilot since it has a smaller area to work on, and then when the piston starts to retreat it exposes a larger area and the chamber then exerts more force and the action of the piston moving back should upset whatever pilot valve there is (spool valve or pop off or whatever) (please please please correct me if I'm wrong).

It may help some people to get this information but I feel that I already know it somewhat well. Thanks!

As far as the crosbar goes, I might try it out, it would help with remote firing as well, at least I've got a while to think about it while I obtain funds XD
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Re: New to hybrids

Unread postAuthor: MrCrowley » Mon Sep 08, 2014 6:04 am

~NooooooB~ wrote:I believe I have the concepts all down pretty well, with the pilot exerting such a force of the larger surface area on the back of the piston and then the chamber having to go up to a higher pressure than the pilot since it has a smaller area to work on, and then when the piston starts to retreat it exposes a larger area and the chamber then exerts more force and the action of the piston moving back should upset whatever pilot valve there is (spool valve or pop off or whatever) (please please please correct me if I'm wrong)

Yeah you have it down. Actually I'm pleased, wasn't sure if people were just learning how to make piston valve hybrids rather than learning how they actually work.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Mon Sep 08, 2014 7:00 pm

There's always a huge difference in abilitly, performance, efficiency, all sorts of things really when you actually know how something works, rather than simply using it. (For me at least)
Another round of questions (sorry :shock: )
I'm thinking about making a piston in three parts (having it machined at least), it'll be like a simple one people make from nuts and washers, except the o ring areas will be machined and a little thicker overall than regularly. The last part will be the support behind the sealing face, is this a good idea? I figured it would minimize weight while not sacrificing performance. On the other hand I'm not sure how it might take from stability of it or the strength of the back area that will slam back?
I'm sorry but I don't have any drawing or rendering programs, the best I can do would be mspaint or by hand, that being said I'd be happy to post either if needed
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Re: New to hybrids

Unread postAuthor: MrCrowley » Mon Sep 08, 2014 9:10 pm

Yeah that sounds like a good idea. Think someon has done it before but can't recall their username or the name of the cannon
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Tue Sep 09, 2014 7:47 pm

Thanks!
Have any idea where I can get a decent remote switch? I found one that looks a lot like yours (MrCrowley) but I get a lot of people saying it's junk or it doesn't completely turn off or other things. I found a couple more but not many and with similar negative reports, and what do you use for a battery? A lot of people stated that they got maximum performance from these special batteries or something, I'm not sure if you need to be spot on with the current or not.
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Re: New to hybrids

Unread postAuthor: MrCrowley » Tue Sep 09, 2014 8:00 pm

It is a bit finicky, sometimes it doesn't respond to the remote to turn off but I figured the main thing was that it turned on when I told it to (which it always does). Previously, I've used a doorbell circuit which worked great. Problem was it required more money, components, and skill to make. I used a 3V relay that was triggered by the doorbell but these relays were quite hard to find and very small; making them prone to damage.

I've considered going back to it but would prefer to use a 5V relay (much easier to find and much bigger as well). Not sure if any doorbell circuits run off 5V but maybe I could work out something.
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