pneumatics for featherweight

[Garfie489]

I've seen an accident on youtube, in India I believe, and the injured kid is lucky to have got away with his life.

Heres a link for anyone whos not seen it

http://youtu.be/qjxCX83Cr1Y

[maddox10]

haha well you are right, here robo wars is a new thing, so not many people are good at it.

That doesn't make it safer...

Anyway, liftoff, the 150psi pressure we were talking about before is the pressure that is regulated to the cylinder or which is stored in the tank? if that is it , then what psi pressure we store in paintball tank?

A properly filled paintball tank has a pressure depending on temperature, that is why you need to fill it on weight, not pressure.
@20°C it's 750 PSI/55bar
@35°C it's 1000PSI/70 bar

[Liftoff]

And this is why I prefer you not going the pneumatic way...too many things which could go wrong, its not like charging a car tyre

[Rahulvyas]

oh, i got it.
@maddox, i suppose we dont have control over temperature, do we?

secondly, if we store 750PSI in the tank and every shot takes 150psi, so we have about 5 flips only?

[Liftoff]

No you have no control over temp, but that goes to show you that there is no fixed pressure at which you store liquid co2, and highlights the importance of a properly rated storage tank.
As to the number of flips, thats not the way to calculate it. Remember this is not compressed air...if it were air you'd be correct. Liq Co2 is a gas in liquid form so you got much more volume of gas when it evaporates. Ie more flips

[Rahulvyas]

so when the air passes, the liquids again gets converted to gas, nice.
and is QEV necessary?
BTW, my cylinder says 10bar, is it ok? ( company- Janatics )

[Liftoff]

Its possible to know the no of flips you can get from a tank...an approximate calculation anyway...
Lets say you have a 12oz paintball tank and a 50mm x 75mm bore x stroke ram. So you start off with a supply of 12oz liquid Co2 at about 20deg C, and a ram volume of 0.15lt

Density of LCo2 at 20'c=27oz/lt
Density of Co2 gas at 20'c at 8 bar=0.535oz/lt
Ram can hold 0.08oz of co2 at 8 bar.
mass co2 tank/mass co2 ram (at 8 bar) = no of flips
12oz/0.08oz=150flips approx.

[Rahulvyas]

man this is helpful now, am impressed with the performance of Co2 compared to compress air
is there any cheap way than buying a filling station?
is there other way of filling co2 other than using fire extinguishers?

[Eventorizon]

I am not a pneumatic's person myself but as CO2 is far better in this regard than air, this is manly due to its stability as air is (as you know) is a mix of gasses and will not compress to a liquid. (evenly at least) CO2 will do it reliably and consistently.

Even better for this is nitrogen, that is capable of even higher pressures (3000psi +) when it goes from liquid to gas. but it is also illegal to use in machines over here for that very reason. It could easily blow most systems apart.

We have a 10 bar pneumatic set up for an axe robot and even at that now pressure I know if I make a mistake it could be fatal.

As for filling, we have a massive CO2 tank in the garage, in the same size tank you have for argon when welding. Basically a filling station. You may need a few adapters but its not that hard. But never go making your own! And most people use fire extinguisher tanks here as the ratings are known and they are designed to be safe from the outset.

[Liftoff]

A fill station off ebay costs nothing, and that's the cheapest way...your other option is to go to a paintball shop and have them fill the bottles for you.
Cant think of any other way tbh

[Liftoff]

http://www.ebay.com/itm/New-Paintbal...item5b035321c4

There you go, at 19$ if that ain't cheap then I don't know what is!
I prefer a Co2 fire extinguisher as a supply tank, once it empty I give it back to the supplier and he just refills it.

[Rahulvyas]

Yup ok
I will get the things then will update this thread, thanks

[Rahulvyas]

Okay, i bought the tank( it weights 1300g non filled and 1700g filled), made of steel, and has testing pressure rated at 250bar, bought from a soda machine vender for 5$(pretty cheap)
so 400g of co2.
Now any modifications i need to do?

[Liftoff]

Wow! So you're building a 6kg robot and get yourself a 1.7kg tank! As I previously explained, you don't need a tank that big/heavy, a 1/2 kg of liq co2 will last a lifetime for the size of ram you plan to use. Also as I have already told you, the thread on a soda bottle is unusable, you need an adaptor like this:
http://www.ebay.com/itm/Sodastream-B...-/161034825292
which will cost you more...in the end, it would have been cheaper, better, lighter, smaller to get a 9oz paintball tank!

[Rahulvyas]

haha no i dont have to buy that, I think I will get some welding done for the fitting I need...
In india we have to make the stuff ourselves, not everything is available here