Directly using liquid co2 in flippers. I've been talking about this with a few people, lets get a discussion going out in the open.

The main advantage i can see is the lack of need for huge burkert and shuttle style valves, instead replacing them with much smaller 3mm orifice or so cryogenic co2 valves.

Doing that also shifts the cooling of the system from the main tank/buffer where it will have a large affect on the systems pressure to the valve/cylinder itself where it should have less of an affect.

Practically, freezing the valve shut/open with the dry ice "snow" created could be a problem. ditto with actually causing the cylinder to sieze from the huge temperature drop that would probably be created within it.

Just dumping a full 600g of gas from a paintball bottle seems to create a lot of this snow, but its very weak and easily breaks apart in your fingers. Makes me wonder if a strong enough shuttle valve would be bothered by it, considering there is at least 100kg of force keeping it shut.

So i am thinking of using my now defunct 50mm bore ram as a test mule. Perhaps just filling it up with a metered amount of liquid co2 and giving it a few fires and seeing if the uhmw shuttle valve freezes up + see if theres a power improvement as a starting point.

Thoughts?
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Marauder was fired once with liquid CO2 in the valve. There was an improvement in power and the valve shut after firing, if memory serves. Repeated shots might cause freezing in the valve.
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So even the rain that falls isn't actually going to fill our dams and our river systems

Put an orifice smaller than the valve after the valve itself, the CO2 will stay liquid until it goes through the orifice (mostly). It'll also keep the cold point outside your "delicate" valve area.

The biggest issue is freezing water out of the air onto/into things. I don't know how much of an issue that would be for robots though. If its an issue (probably more of a problem in summer tbh, as there is more water in the air) then look at something like a cryogenic grease coating on your moving parts.

If you do liquid injection from a safety POV the only concern I have is you are potentially making the ram a pressure vessel. I'd look at adding a pressure relief valve and a burst disk to it if it's not going to be able to hold 1000-1400PSI.
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Mechanical engineers build weapons, civil engineers build targets

Having seen the construction of Glens ram, I would trust it as a pressure vessel over a paintball tank
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https://www.halfdonethings.com/

http://www.warpig.com/paintball/technical/gasses/co2dynamics.shtml

Here's a good concise explanation of the basics of Co2, especially the bit about fill %. Quite a handy resource
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Before reading this thread I though CO2 power would be way too hard, after reading it I want to build a bot with it.

Question is, do you guys have any trouble getting paintball gun parts in our nanny state?

Tanks, regulators and stuff is fine. Just not the gun part but we don't need that anyway. Low pressure is easy, full pressure not so much.

The main problem is the cost of gas you either need to buy a tank which is quite expensive or hire one also quite expensive. I had one a while back but I just couldn't justify keeping it for a bot I only fought with every 3 - 6 months.
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Steven Martin
Twisted Constructions
http://www.botbitz.com

I'll have a chat to whoever I buy the paintball parts from, but is it possible to fill the tank with dry ice (which I can buy relatively cheap) and just let that pressurize the tank?

Short answer no... Long answer maybe......

I think your probably going into territory which gets dangerous and requires custom pressure vessels. Regardless its not the sort of setup which I think would be acceptable to have at a public event. Just from a safety perspective.
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Steven Martin
Twisted Constructions
http://www.botbitz.com

$369 to buy a D size bottle of CO2 at Gasweld and a refill is $49.

http://www.gasweld.com.au/catalogue/docs/speedgas.pdf
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https://www.halfdonethings.com/

@ Ondray.

Yes, it is possible.
But no, it isn't safe. Undoing and tightening the storage bottle every time you fill it with the right weight of dry ice will wear out the thread in the aluminium bottle rather fast.
It also takes only 1 bad alignment to destroy the thread.

Also, filling the bottle trough the small hole is "fun".... Small chips and a funnel spring to mind.
And then the waiting to get the bottle to ambient will be tedious.

@ marto, I find FP a lot easier than fiddling around with regulators that can't handle liquid CO2.

But on the other hand, i'"m biased.

Don't buy the co2 bottle, rent it from BOC where at worst its $36 for the gas + $12 a month rent for a 15kg one. I buy them one month before and take it back one month after Or just split the cost with another builder bringing a tank (hint hint haha)

The paintball bottles can be bought in the country as can the regulators. Mind you it seems 12oz and 20oz are all that can be easily had. The other sizes are unobtanium!

Pneumatic rams, valves, safety valves and so on can be had from ebay and ali express very cheap. Check Daniels build thread, he just bought a full setup for next to nothing
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

You should be able to rent the bottle for just the amount of days you need rather than a whole month.
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So even the rain that falls isn't actually going to fill our dams and our river systems

Sounds like the rent a CO2 bottle path is the cheapest and safest,

But my searching did bring up soda-stream bottles, which are expensive at about $50 online or $25 from dick smith for one bottle but includes the CO2 (about 400gm) - you can get adapters off ebay to hook them up to paintball kits real cheap so I'm going to research this further.