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Semi-Auto Pneumadness

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#26 Draconis

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Posted 04 March 2011 - 08:12 PM

@Draconis: Modify? It's just a matter of threading on one of these adapters and possibly removing the valve core from the propane bottle to improve flow. No big deal really. In fact I made this same suggestion to Doom some time ago as an alternative to his Catalina cylinder.


The universal danger of flammable gas is why we rejected that idea. That and the retarded flow rate through such a small orifice. There are many better options for reuse of old tanks. How about nice steel or aluminum paintball tanks? I have had luck getting some which were out of date and thus not suitable for CO2 use anymore, for FREE. Or empty disposable fire extinguishers? They have nice aluminum bodies available in various sizes and are, again, FREE.

Yes, the only downsides to using throwaway propane cylinders are
1. You have to empty them using a camp stove, then finish it by venting it outside for quite a long time. Make sure to tie or weigh it down with something, then depress the valve stem using the tank fitting adapter to vent it out. DO NOT HOLD THE TANK WHILE DOING THIS, it will get cold enough to freeze your skin to it because the propane is undergoing a phase change from liquid to gas. Also obviously do it away from a flame source.
2. Even after being emptied they smell.



Yeah, that isn't really an accepted method for evacuating a cylinder of flammable gas, and that is EXACTLY why I suggested not posting it. This is against my better judgement, because I can just see some doing something wrong and freezing off their finger, bowing up their face, or gassing themselves to death... You need to remove the schrader valve completely and fill the entire tank with a non-flammable liquid. Water works and is cheap. The tank must be completely immersed and left upright to vent for at least one hour. There will continue to be propane that exits the metal structure of the tank during that period. Do NOT pressurize air in a cylinder that has not been liquid displacement evacuated, as it has a possibility of igniting the propane still embedded in the tank walls.
You guys have met some of our members, right? Would you really trust them to be doing something like this? And to know when they should NOT be doing it? So go ahead, be cavalier with the retards. None of them live near me anyway.

Edited by Draconis, 04 March 2011 - 09:04 PM.

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[15:51] <+Noodle> titties
[15:51] <+Rhadamanthys> titties
[15:51] <+jakejagan> titties
[15:51] <+Lucian> boobs
[15:51] <+Gears> titties
[15:51] <@Draconis> Titties.
[15:52] <+Noodle> why is this so hard?

#27 taerKitty

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Posted 04 March 2011 - 08:29 PM

It will make the mods life easier, and improve overall post quality if some of them are AFK, permanently or not.

Back to the mod, I'm surprised it only gets 6 shots. I think the Sceptor has about the same size tank, and it runs at lower pressure. Then again, it's a very fast valve, not a hi/low tank setup.

How much does it weigh? I'm assuming the standard stance is one hand on the joystick, the other on the pump handle. Those pump handles tend to flex, in my experience.
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#28 CaptainSlug

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Posted 05 March 2011 - 08:06 AM

I'm not going to advocate any particular tank. As with any pneumatic project you and you alone are responsible for whatever level of risk you put yourself in.
I just used what I had available for cheap and that would seal easily. Ideally I could just make one since I can weld my own fairly easily.
I'm not sure of where to source used fire extinguishers, and they will require modification.
The local paintball shops are very safety conscious and any outdated or uncertified equipment either gets recycled or locked away.

1. Back to the mod, I'm surprised it only gets 6 shots.

2. How much does it weigh?

1. That was the minimum goal, not the end result.
Preliminary results show 9 shots at 40psi.
A better regulator and further adjustments should improve that number.
2. As answered previously, around 4lb. If I can switch to a manual valve and make some other changes I can hopefully reduce that some.

Edited by CaptainSlug, 05 March 2011 - 08:29 AM.

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#29 roboman

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Posted 27 March 2011 - 02:12 PM

I know the topic is a little old, but I thought this was pertinent.
Instead of a propane tank, why not use a plastic one? That one is 44 in^3, rated for 125 psi working pressure, and bursts at 500 psi. It's also really light, fairly inexpensive, and has 1/4" NPT ports on the ends.

Edited by roboman, 27 March 2011 - 02:13 PM.

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#30 Doom

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Posted 27 March 2011 - 02:53 PM

I think the reason no one uses those tanks is that they never saw them before.

Personally, I'm wary of using plastic for pneumatic applications, but as this one seems to be a serious engineered product, I'm less wary of this. Have you tried this tank yourself roboman?
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#31 roboman

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Posted 27 March 2011 - 08:39 PM

I think the reason no one uses those tanks is that they never saw them before.

Personally, I'm wary of using plastic for pneumatic applications, but as this one seems to be a serious engineered product, I'm less wary of this. Have you tried this tank yourself roboman?


No, I haven't tried it personally, but it was recommended to me by a FIRST robotics team at the LA regional this weekend. The regulations for the pneumatic systems on FIRST robots are incredibly strict - take it from me; I designed the system on my team's robot. Those tanks are very tough, and for the price, they can't be beat.
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