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#31
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Re: Are we allowed to use helium?
Helium is mined.
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#32
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Re: Are we allowed to use helium?
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Maybe one day we'll be able to harvest it from fusion reactors as well (or the sun). |
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#33
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Re: Are we allowed to use helium?
which brings us to...
do you REALLY need to use that helium?? SAVE THE HELIUM!!! ![]() |
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#34
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Re: Are we allowed to use helium?
Quote:
Last edited by ToddF : 29-03-2013 at 21:58. |
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#35
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Re: Are we allowed to use helium?
...Now i'm wondering if I could put enough helium in a pneumatic tire to make it float. R78 doesn't say the pneumatic wheel has to be serving a 'wheel' purpose, and a floating pneumatic wheel would be just as effective as a balloon at getting in the way.
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#36
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Re: Are we allowed to use helium?
Even if there isn't a rule about it, I don't see a point in it. If you're over on weight, start making swiss cheese.
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#37
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Re: Are we allowed to use helium?
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It would take ~46 cubic feet of Helium at NTP to raise a 3 lbm wheel. |
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#38
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Re: Are we allowed to use helium?
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I realize I'm lawyering, but that's kind of the point of this discussion, no? I would tend to agree with Tristan's view that using a balloon *may* not constitute a violation of the pneumatics rules, but its certainly a grey area. For years, the pneumatics rules forbade pneumatic wheels without specifically calling out an exception, but teams USED pneumatic wheels. Nobody noticed that the way the rules were written forbade them, because nobody thought of a pneumatic tire as being a pneumatic device. |
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#39
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Re: Are we allowed to use helium?
Interestingly, adding helium to a fixed volume will make it LESS likely to float. In the case of a mylar bag, the maximum lift potential happens when the bag volume just reaches its maximum. If you keep pressurizing the bag, you are adding more gas mass, but keeping the volume fixed. Density increases, causing a loss of lift. If the bag were strong enough, it would be possible to pressurize the bag to the point where the mass of helium in the bag would be greater than the air it displaced, actually making the bag sink, rather than rise.
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#40
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Re: Are we allowed to use helium?
Quote:
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#41
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Re: Are we allowed to use helium?
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?
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#42
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Re: Are we allowed to use helium?
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Also, the 1 atm specification you mention—although reasonable—is not stated in the rules, and to my knowledge has never been articulated by FIRST. As a result, teams may wonder why other indications of FIRST's intent aren't really in harmony with that specification:
By the way, since I didn't really explain my rationale earlier: the energy source rule covers forms of energy that are "used" (I presume this means intentional energy release during a match). Every robot can catch fire: that doesn't mean we prohibit every single robot because it's a source of (chemical potential) energy not enumerated in the rules. By the same token, if popping a balloon is an unintended failure mode, there's an equally good case that that energy release is not use, and thus not subject to the energy storage rule. The safety rule covers it adequately. With regard to the compressed air source rule, it uses the word "air", and so I have a hard time accepting that it covers gases that are not (in any conventional sense) air. As others have noted, calling commercial-grade helium air is as bad as calling it natural gas, uranium or starstuff. Quote:
I distinctly remember a team using the Skyway Ø8 in pneumatic wheelchair wheels in 2001, and many teams using them thereafter. (I suppose they could have been filled with something else, but I kind of doubt it.) I think the flowchart was called out as enforceable by a numbered rule in some years, but in others it was merely appended to the manual and was ruled advisory (like a Q&A response). |
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#43
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Re: Are we allowed to use helium?
Alan,
Whenever a team used a part that was not covered by the rules, the inspectors used the flow chart to determine it's legality. Remember that materials were far more restricted in the past than they are today. Teams actually used packing material in the KOP because anything in the kit was legal. 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. As to robot rules, I have electronic copies back to 2001 and in that year materials you could use on the robot were limited... 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". 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) Last edited by Al Skierkiewicz : 30-03-2013 at 09:08. |
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#44
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Re: Are we allowed to use helium?
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Pressure is the sum of the forces from all gas molecules hitting the container walls, divided by the walls' area. Thus, it is proportional to the number of collisions per unit area, and the velocity of the particles. The latter is temperature, which we're ignoring. The former is based on the container surface and the number of gas molecules. In elastic balloons, these two do not rise proportionally, because the internal pressure is balancing not just the external pressure, but also the the elastic potential energy of the balloon. In a mylar balloon (not overly inflated), the internal pressure is not compensating for elasticity, so the two pressures are in fact equal--the increasing volume exactly compensates for the increasing number of gas molecules. So it's not that there's no force acting on it, it's that the force in P=F/A is increasing exactly proportionally to A. ...Maybe. <Is about to be killed by Ether> EDIT: Hey, hey! It's seems that someone actually did this experiment. See page 3, it is indeed constant at 1atm. Who'da thunk? I was not expecting to get that right. Last edited by Siri : 30-03-2013 at 10:42. |
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#45
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Re: Are we allowed to use helium?
Siri,
Thanks for trying. What I am trying to understand is this. You have a volume of gas at 1 atm. You have a deflated balloon, flat, no internal volume. The inside and the outside of the balloon are also at 1 atm. The volume of gas is connected to the balloon with a hose or tube. Explain how the volume of gas will somehow expand the balloon and fill it if all pressures are equal. This is what was proposed earlier in the thread. I see no force that will impel the balloon to inflate and for the gas to pass from one volume to the other. |
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