Air resavor rules

Are you allowed to put cold air (say -65 degrees) in you air resavor to be able to put more air in it?

If you filled your reservoirs with cold air up to 100psi, and the pressure in the system raised above 100psi as the air heated to ambient temperature (which would be pretty much inevitable, hopefully no tournaments will be held in below-zero environments), that would be a violation of R25.


Any question that starts “are we allowed” must be answered by looking in the game manual:

Assuming you have actually read the game manual, what rules do you think you might be violating, aside from potential violation of R25 (when the air warms up and explodes your tanks), or maybe S-1 and G3?


You forgot S1 - if you come to the field with a robot that is super frozen, I might consider that unsafe robot to the volunteers that might have to handle it.


Well well well, it appears as if someone forgot the ideal gas laws.


R25 (so helpfully quoted above by holbrook) uses the passive tense (may only be charged to a maximum of 100 psi). I would read that to mean that if at any point the charge in the reservoir exceeds 100 psi, the rule has been violated.

If the tank is filled with air at a temperature of -65 F to a pressure of 100 psi and then raised to a temperature of 70 F, the pressure in the tank will rise to about 140 psi. I suspect this would be considered a violation of R25.

Additionally, I suspect the very conspicuous condensation and/or frost on the tank would be a hint to the officials to look closer.

For the curious, for pressures in PSI and temperatures in F, the equation for pressure change is:

((P1 + 14.7) * (T1 + 459.67)) = ((P2 + 14.7) * (T2 + 459.67))

14.7 psi is generally considered atmospheric pressure at sea level.
459.67 is the difference between 0F and absolute zero ( see


Of course, the other strategy is to use a gas that liquefies at less than 100 psi at room temperature. Unfortunately, the most commonly available choices have … other issues.

Propane exceeds 100 psi at a temperature of 64 degrees. At 85 degrees (which could happen in a hot auditorium) it is at 140 psi.

Butane would be a lower pressure, being about 40 psi at 65 degrees, 60 psi at 85 degrees and 100 psi at about 120 degrees.

If you can store a pressurized liquid in the tank and draw it off as a gas, you can theoretically use far less volume per actuation. This would require very careful planning to make sure your tube exits the reservoir at the highest point (to avoid drawing liquid).

The even bigger issue is that both of these gasses are rather … flammable, so they would definitely fail S1.


Did this somehow merge into the Worst Vex Idea ever thread?

Well kids, I remember back in 2020 naw maybe 2021 where we needed a few more PSI to run those last two piston grabs and we settled on using liquid propane, we had lots from Chucks dad’s BBQ business and we started using that. So we had frost issues on the sides of the tanks, so we’d do a quick swipe to pull the frost off the dual tanks to keep the refs from asking questions. It’s the semifinal and wouldn’t you know it our partner has got that Acrylic panel and with the rubbin an juking of that robot it was putting off sparks 11’ wide. So of course it done lit up that tiny Propane trail we were leaving, and boy howdy, did that fireball roll up into the sky. :grinning:


You, sir, get the nomination for comedy gold…


VEX Worlds game manual update changes he field perimeter to the Battlebox image


Isn’t Tesla a VRC sponsor? Didn’t Elon want to sell flamethrowers?

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And that’s how I got this scar…