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).
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.
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.
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.
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.
Thanks for the discussion. I am the poster of that Q to the Q&A. This is the product I was referencing:
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?
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…
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.
As a robot inspector, absent better guidance, I was accept something labeled as a gas spring as a gas spring. To me. the Macmaster Carr is a gas spring. As opposed to a mountain bike gas shock, which is also a gas spring, but the QA has ruled the oil shock part makes it illegal. A little strange because the rule specifically allows a gas shock. All the gas shocks I know of use oil as the energy absorption mechanism required for shock absorption. So before today I would have considered a mountain bike shock legal. Your inspector may vary.
Lets hope somebody makes this clearer. This kind of vagueness isn’t fair for teams or inspectors.
I don’t think they meant to outlaw gas springs like those from McMaster. Teams (including mine) have been using them for years to counter balance arms, or make passive mechanisms (after match climbs, etc).
I’m not sure why they would outlaw sealed gas shocks either, like those on mountain bikes, seems pretty hard to get the fluid out of those by accident but I guess in some cases I could see why they could be ruled illegal.
They definitely need to clarify this. We have a couple places on our robot where we are considering gas springs, if we have to make some other linear spring mechanism it will be a lot more work.
It seems that my question was not specific enough for the Q&A. I tried to avoid the response of ‘we don’t comment on robot designs’. Perhaps I should have included a link to the McMaster site.
From what I can see from the limited number of diagrams online, none for the SUSPA Gas Spring I bought or very helpful, the oil inside is just for lubrication, and not for mechanical advantage.
I guess I’ll either submit another Q or keep my fingers crossed.
Tom,
The response to your Q&A appears to be a perfect definition of the linked McMaster product shown above. It is at least one of the products we discussed when this rule went into the robot rules. The linked page showing cross section is in my opinion, a ‘not to scale’ drawing to indicate the correct use of this product based on seal lubricant. The lubrication of the seal is essential to the expected life cycle of the shock. This “lubrication oil” is under the same rule as other lubricants in R17.
This answer does point to fluid filled shocks which do not meet the rule.
