Quote:
Originally Posted by Tristan Lall
There seem to be some errors in the information being given here. Let me try to clarify.
Flow control fittings are permitted (if they are "connecting fittings"). Flow control valves (and check valves, incidentally) are not permitted (because they're not any of the things permitted by <R66> and the rest of the pneumatics rules).
The fittings Chris was referring to are like an NPT-to-tubing elbow connector, with a needle-type adjustable flow control screw built in. Those are almost certainly legal, because they are usually understood to be a type of fitting. A flow control valve, that isn't also a fitting, is almost certainly illegal.
At an off-season event, do whatever the organizers require. If they're alright with teams taking reasonable liberties, go right ahead. (Usually there's no inspection.)
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Tristan: That makes a lot of sense to me. Thanks for pointing out that distinction between flow control
fittings and flow control
valves. This afternoon, we ordered some flow control
fittings, with 1/8" NPT ports that screw right into the exhaust ports on the Festo valves. As fittings, those would seem to be within the spirit of the rules.
Interestingly, there was actually a
question on the official Q&A about the legality of using flow controls. The questioner pointed out that in the
Pneumatics Manual Rev B for 2011, the sample pneumatics diagram on Page 8, and the photos on Pages 9-10, show flow control fittings screwed into ALL of the cylinder ports. These are the NPT-to-tubing fittings with the needle-type flow control screws that you referred to above. But somewhat confusingly, <R66> seems to say that only the items it specifically lists are allowed in a pneumatics circuit on the robot, and flow controls are not specifically listed in <R66>. The questioner
asked for a clarification on this apparent contradiction from the GDC. Unfortunately, the GDC's response was simply that "All pneumatic valves must comply with Rule <R66>," which still (to my mind) would seem to leave the answer ambiguous.
The wording of <R66> seems to add to the confusion, since it simply provides a list of "pneumatic system items" that are "specifically permitted," and <R67> lists pneumatic items that are prohibited. But what about the pneumatic items that are in the "no-man's land"; i.e., not shown on either the <R66> list or the <R67> list? Strictly speaking, it would seem that both flow control fittings and flow control valves are in this no-man's land.
However, <R66> Paragraph E does allow for unaltered COTS "connecting fittings" with a working pressure of at least 125psi. Does a flow control fitting that also provides connection to a tube count as a connecting fitting (which is legal), or is it a pneumatics part that provides extra functionality and thus it not permitted because it is not specifically listed as permitted in <R66>?
The point is mostly moot, because the official competitions are over for the year, and as you point out, most off-season competitions don't even do inspections. So, we'll feel free to use flow control fittings and not worry about it. But I kind of wish the GDC had made an explicit ruling to allow them. Maybe this ambiguity will be cleared up in next year's competition.
Thanks again for your thoughtful (and helpful) response, and for clarifying the difference between the two types of flow controls.