Gas springs and Q&A #Q695

[martin417]

I just read this Q&A:

Game Manual - Robot » Power Distribution
Q695 Q. R35 allows for "closed-loop COTS pneumatic (gas) shocks" on the robot. Would a closed-loop "gas spring" that contains oil within its sealed housing meet the requirement of R35 and not violate the R9 ban on hydraulic fluid?
FRC4276 on 2016-01-28
A. No, a shock containing oil, other than minuscule amounts for lubrication, is not considered a pneumatic shock.

It would appear that there is a misunderstanding as to how a gas spring is constructed, ALL gas springs contain oil, and more than a "minuscule amount". Gas springs have been legal in the past, but this answer seems to make them illegal. If you look at the attachment, you will see that there is more than a little oil in a gas spring, and in fact that oil restricts the way a gas spring should be used. (always rod down).

[Hadi379]

To me the oil is there to only keep the seal lubricated. It doesn't seem like there is a lot of oil. Its only about an 1/8 of the way filled from what I can tell.

[martin417]

Originally Posted by Hadi379

To me the oil is there to only keep the seal lubricated. It doesn't seem like there is a lot of oil. Its only about an 1/8 of the way filled from what I can tell.

The way the question was worded,

...that contains oil within its sealed housing...

Is pretty clear. All gas springs "contain oil within their sealed housing". The GDC did not define "a minuscule amount", but I would say that if there is a pool of liquid oil in the housing, there is more than a minuscule amount, and therefore this answer makes pneumatic springs in general illegal.

I don't believe that is the intent of the GDC, I just believe that there is a lack of understanding of the construction of a gas spring.

[notmattlythgoe]

The Q&A people seem to be using really really strict interpretations of rules lately.

Another one is with the vouchers and only getting credit for the items you specifically ordered with the voucher.

[MrForbes]

The brochure you link to appears to be an "artist's rendering" of what it really looks like inside a gas spring.

I think that the Q&A is talking about gas filled shock absorbers, and you are talking about gas springs. One has quite a bit of oil, and the oil is used for damping over the entire stroke, and the gas is used only to reduce aeration of the oil. The other has gas in it as the working medium, and oil is used only for lubrication.

Some folks just ask too many questions!

[martin417]

Originally Posted by MrForbes

The brochure you link to appears to be an "artist's rendering" of what it really looks like inside a gas spring.

I think that the Q&A is talking about gas filled shock absorbers, and you are talking about gas springs. One has quite a bit of oil, and the oil is used for damping over the entire stroke, and the gas is used only to reduce aeration of the oil. The other has gas in it as the working medium, and oil is used only for lubrication.

Some folks just ask too many questions!

I do understand the difference, but others might not. I know that the purpose of the oil in a pneumatic spring (gas spring) is to lubricate the seals (hence why the spring must be used rod down). But the answer given by the GDC is not clear and could lead some to believe that pneumatic springs are not legal.

[MrForbes]

You're probably right, and thanks for bringing it up!

[SenorZ]

Thanks for the discussion. I am the poster of that Q to the Q&A. This is the product I was referencing:
http://www.mcmaster.com/#4138t58/=10vr03y

Of course, when I bought them I didn't read the description thoroughly, because it seemed EVERYONE on CD said gas springs like those used in car hatchbacks were legal.

Then I saw that that they had oil in them, and that the oil is listed in the description under "Force Mechanism". Which implies a hydraulic dampener for the gas spring. Essentially the oil is there to slow the restoring motion of the rod.

Any refs out there? Have you told a team they are NOT going to pass inspection because they had this type of gas spring?

[Jon Stratis]

Originally Posted by SenorZ

Any refs out there? Have you told a team they are NOT going to pass inspection because they had this type of gas spring?

you mean inspectors

Personally, my team has used gas springs before, quite possibly the same ones you linked (another mentor obtained them, so I can't be sure, but they look the same to me!). I wasn't aware that there was any oil in them other than that needed for lubrication. I kind of want to get one now and cut it open to see how much is actually in there...

Maybe we can get Al to chime in here!

[MrForbes]

I think that you'd be hard pressed to find someone on a team who has ever seen the oil in a gas spring! I think there is a warning on them about "DO NOT OPEN THIS", you know.

[martin417]

Originally Posted by MrForbes

I think that you'd be hard pressed to find someone on a team who has ever seen the oil in a gas spring! I think there is a warning on them about "DO NOT OPEN THIS", you know.

If you go to any older SUV (like my 2003 Tahoe) and open the tailgate, take a look at the rods on the gas springs. I would bet that you would find plenty of oil on the rods, past where the seal wipes the rod. I know you can see it on mine.

Also, I know many wood-turners that swear by home-made lathe tools made from the rods of gas springs. Extreme car must be taken when "venting" the high pressure gas.

[MrForbes]

Hmmm....my older SUV was built in 1957, they hadn't invented that yet!

But that's a good point, if you use your robot daily for ten years, you might leak a drop or two of oil.