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I would like to know how a LEGO pneumatic engine would perform when powered with a nitro (N2, HPA) or CO2 tank. I have seen a few RC cars powered with air (from soda bottles), so I am wondering if it would be advisable to power such an vehicle with a much more powerful but also heavyer paintball tank.

There are few pneumatic engines designs, like this Lego Pneumatic Engine switchless LPE-V4-DIHC or this Lego 1500 rpm V8 or this (defective) LEGO V8 pneumatic.

LPEpower Pushrod V8 engine

I am not building one yet. But I am very... very curious about how effective such an engine would be when powered with a paintball tank... for how long would it be able to run? Has someone already tried that?

There have been RC cars with LPE engines but all I have seen was powered with soda bottles. I am planing an RC car of my own and I'm going with a simple electric solution but, an LPE would be sweet if it worked for more than a few minutes.

Precisions: I would like to know how long such an engine could run with a 45/4500 N2 tank for example.

@Joubarc found that such engines can run with a max of 90psi. The inline-4 on that page runs at max speed with a 4bar (58psi) intake (like most other LPE I saw). It means that we can expect slightly higher pressure requirements if the engine is delivering power to a system.

N2 tanks are simply filed with air which is cheap (when you have a compressor ;) With the example of a 45/4500psi tank how long could the car run?

Also comes the question of the weight, with a carbon fiber tank weighting over 0.8kg is it really a good idea?

Would CO2 be a viable solution? With a maximum of 6bar should I expect condensation in the pistons? Would it really be a problem to consider?

Simply put do you know if this would work. If not, have you heard of any example that was successful or an epic fail?

Edit: I received an answer from LPEpower:

I have no experience with long term running engines using co2 tanks, but the engines do run fine with them. Perhaps you could warm up the co2 coming out of the cartridge a bit, to prevent condensation. The real danger in my opinion is the low temperatures that the expanding co2 gas creates. Those are not good for the rubber seals. So if you'd manage to heat up the gas using a coil wire wrapped around the intake tube, connected to some batteries, you could prevent that from happening.

I guess I should probably forget about the CO2 and invest in some HPA gear.

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You could power it with a LEGO compressor :-/ –  Joubarc Nov 6 '11 at 16:13
@Joubarc could, but it defeats the idea of running from a pneumatic engine if you need another engine and power source to power it. –  Coyote Nov 6 '11 at 17:47
Hence the smiley. That said, it's not totally nonsensical if only for educationnal purposes. –  Joubarc Nov 6 '11 at 18:02
Sorry I wasn't attentive yesterday :) –  Coyote Nov 6 '11 at 23:19
Please take proper precautions! The on-tank regulator of the compressed air tanks used for paintball typically output close to 800 PSI (55 bar), and even "low-pressure" tanks output around 400 PSI (27 bar). You will absolutely need a secondary regulator to avoid creating LEGO shrapnel! –  harbichidian Nov 10 '11 at 22:50
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1 Answer

Apprently, it is possible to generate up to 37psi with LEGO pneumatics parts only.

LEGO penumatics can withstand more, however. Engines similar to the one you want to build can work with a recommended pressure intake of 90psi; a maximal (but not recommended) of 120psi is mentionned.

So I think it all boils down to the pressure your N2 or CO2 tanks can generate, under 100psi should be OK. If not, I suppose there could be some way to get it down to that level.

As for using N2 or CO2 instead of air, I don't think there is much reason for concern, since both are faily harmless and present in air anyway.

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I am not sure about CO2... On a few occasions I have noticed "snow" coming out of my markers. When the marker gets some liquid CO2 from the tank (or from condensation?) it tends to shoot pellets faster with white jets of CO2 coming out of the muzzle. The way CO2 is expelled in violent successive releases might be why it happens. I'm not sure about what would happen if the gas was released uniformly. That's why I really would like to have an answer from someone who tried that kind of thing. –  Coyote Nov 6 '11 at 23:17
Also currently this is more of an "academic" question as I don't intend to build one of these immediately... I might end-up buying one from LPEpower as I don't have the parts, the time, tools and experience of modifying the required parts to get one running properly. So before investing in parts that are heavily modified I want to make sure this is a viable/fun solution. –  Coyote Nov 6 '11 at 23:29
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