Chief Delphi - Are we allowed to use helium?

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Quote:

Originally Posted by Alan Anderson (Post 1254463)

Was there ever a year when the flow chart was considered to have the status of an actual rule, rather than being a (possibly incomplete) summary of the rules?

But what if the rules *themselves* were written in helium?! I'm fairly certain this would enable some kind of time-space paradox that the GDC only simulated once during game season planning, and might require a firmware update on our bridges...

Re: Are we allowed to use helium?

Al,

A 1 mil thick sheet of Mylar weighs about 5*10^-5 pounds per square inch. So the pressure inside a partially-filled Mylar balloon would be about 0.00005 psi greater than atmosphere. Is that what you are arguing about here?

Re: Are we allowed to use helium?

Quote:

Originally Posted by Al Skierkiewicz (Post 1254577)

Explain how the volume of gas will somehow expand the balloon and fill it if all pressures are equal.

Add molecules at constant pressure to a flexible but inelastic container. The volume increases. I don't see how this is an open question.

A typical mylar balloon has exactly ambient atmospheric pressure inside it. If you manage to defeat the fill port's built-in leakage and overfill it so that it's starting to swell, it actually becomes less buoyant. After a couple of hours, it will have leaked back to ambient pressure.

Re: Are we allowed to use helium?

Quote:

Originally Posted by Al Skierkiewicz (Post 1254556)

Tristan, how can you make a distinction between air and other gases when the rules do not. The rules speak to "air pressure" which is by definition a mixture of gases. Gas shocks are specifically excluded, other devices that contain pressurized gas are not excluded and therefore not legal for use on the robot.

I think the only mixture of gases the rules refer to is air, which isn't an arbitrary mixture, but one with a reasonably-well-defined range of compositions. I'm contending that there is an implicit distinction between air and all gases not mentioned.

Quote:

Originally Posted by Al Skierkiewicz (Post 1254556)

The materials that you are allowed to use to build the robot are limited. There are three sources of
materials:
Sources of Robot Materials Location
1. Parts found in the Kit of Parts Appendix B, Inventory list
2. Parts from SMALL PARTS, INC. SMALL PARTS, INC. Catalog
Appendix D, Ordering information
3. Parts from Additional Hardware List Appendix C

Now I don't have a Small Parts Catalog from that time but I don't remember them selling pneumatic tires. Wheels provided in the kit (and listed in Appendix C) were specifically "5"-8" Ø, Up to 6 non-pneumatic".

I actually just looked back at the 1999 rules, and they suggest that the wheels came from Small Parts—which is not how I remember it either (and a slightly-newer Small Parts catalogue doesn't list them). Skyway provided wheels in some of those years via something like a PDV.

Also, in 1999 there was no language about "non-pneumatic" wheels—so I guess it did arise as an issue at some point.

Re: Are we allowed to use helium?

Quote:

Originally Posted by Al Skierkiewicz (Post 1254556)

Alan,
As to the 1 atm, will someone please explain how a deflated mylar balloon would magically fill up if the pressure inside and outside the balloon are the same? Assuming that gravity and temperature are ignored, convince me that helium gas would magically move to the interior of the balloon and fill it with no other force acting on it. And if that is the case, why would the balloon deflate when it is opened? (Ignoring of course the lighter than air helium gas)

By changing temperature. Helium is pretty close to an ideal gas as far as approximations go, so it will follow the law PV/T = constant. Since the P is being held constant, when the volume increases, the temperature will decrease, assuming the process is conducted instantaneously with no heat transfer. Since the balloons conducts heat, and because the process takes time, you won't see as significant a temperature drop as the naive law predicts because heat will start transferring into the gas as soon as there is a temperature differential.

The force is generated from the difference in concentration of the gases. http://en.wikipedia.org/wiki/Diffusion.

Re: Are we allowed to use helium?

Al is correct about the 1 atm thing, but only in a painfully pedantic way. It does take a tiny (and I do mean tiny, neglecting any fill valve characteristics) pressure differential to cause gas to flow into an uninflated flat Mylar balloon... because the pressure inside the balloon must lift the "top surface" of the mylar as the balloon changes shape from flat to an oblate spheroid. In an earlier post I gave an estimate of the theoretical pressure differential required to do this.