The law of un-intended consequences: rule re-interpretation

[martin417]

Sometimes, rules that are unclear, poorly thought out, or "re-interpreted" have consequences that were not expected or intended, and that go beyod the year they were implemented.

Case in point: Last year, the rules stated that all pneumatic valves had to have an operating pressure of at least (edit) 125 PSI. We found such valves, ordered them ($400.00 cost, 4 week lead time from Japan) and used them on our robot. During the build season, many other teams complained that 125 PSI valves were hard to find, so the GDC decided that as long as the valves didn't fail catastrophically at 125 PSI it would be OK to use them. Too late for us, we had already spent the money and committed to the valves.

all last year we had a leak in our pneumatic system, we never could find it. This year we planned to use the same valves. Again the leak problem. We finally found out that the valves leak a small amount of air to the exhaust port all the time. This is because they are 150 PSI valves that use metal seals instead of compliant seals. We had to ditch the valve and scramble to find something else at the last minute. We ended up with the Festo valves from 2008.

The point of this story is that since we complied with the letter of the rule last year, we ended up at a disadvantage to teams that waited until the rule was changed. We wasted $400.00 on valves that we won't be able to use. we lost several matches we would have won except that a long field delay allowed out pre-charge to leak out so our autonomous failed.

I know the GDC does the best job it can do to lay out the rules before the season. I understand that sometimes the rules need "tweaking". I just find it frustrating when those changes cost us money or put our team at a disadvantage.

[Brandon Holley]

In reference to rules that call for specific ratings, or sizes of parts, its important to utilize market standards. The 150 psi rating valve is a perfect example of this. I'm by no means an expert, but I don't believe that is a market standard that manufacturers work towards. I believe a similar issue arose this year regarding pneumatic tanks and working pressures vs. burst pressures.

[ebarker]

There was an amendment to <R72> here: http://usfirst.org/uploadedFiles/Rob...Update%205.pdf

that allowed the use of an inexpensive relief valve on the low 60 psi side of the circuit to relieve the requirement for an expensive solenoid valve.

In other words you can you a $ 40 solenoid valve in conjunction with a relief valve.

[martin417]

The change I was referring to was in this Q&A:

Documentation for 125 psi rating
Posted by FRC2973 at 02/05/2010 11:50:06 am
In reference to Update #5 and Rule R72-c, I have received confirmation from SMC that their SY3000 series solenoids are "rated" at 125 psi even though their operating pressure is listed at ~100 psi. The documentation is outlined here:http://www.chiefdelphi.com/forums/sh...ad.php?t=81946
Is this documentation sufficient to show that these valves do not require an additional pressurerelief valve?


Re: Documentation for 125 psi rating
Posted by GDC at 02/10/2010 02:07:28 pm
Documentation from the manufacturer is acceptable proof that a part meets specific criteria.
Please make sure to bring a copy of the documentation with you to Inspection.

Which adds an interpretation that even though the operating pressure is below the 125 PSI minimum, it is OK to use a valve that won't fail at that pressure.

An important note: the valve they are talking about (SMC SY300) IS AVAILABLE in a 150 PSI model (the K option). That is the valve we used. It is more expensive, and has a long lead time, but it meets the letter of the rule.