Locking gas springs - legal?

[Jon Stratis]

I would assume they were legal, per the 2016 rules - They are a closed loop gas shock (R35 D). Out of curiosity, what sort of mechanism causes them to lock into place?

[nuclearnerd]

On the Bansbach page, there are a couple versions. Type B uses a valve that interrupts gas flow between one side of the cylinder to the other. They call this "spring locking", since the gas is compressible, and the cylinder locks with some springiness. The other types put the valve in an oil reservoir, which locks the cylinder rigidly (in one direction or the other or both).

The only concern would be whether the latter types would contravene R9, but I would tend to believe they don't count as "hydraulic devices" in the same way as they currently don't count as "pneumatic devices" (R77 blue box) for the purposes of the safety rules.

[FrankJ]

Until this Q&A I would have said that would be legal. But with the Q&A the GDC says maybe not.

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 | 2 Followers
A. No, a shock containing oil, other than minuscule amounts for lubrication, is not considered a pneumatic shock.

[nuclearnerd]

Well that sucks. These would have been such a useful product (easier to integrate than disc brakes for holding arms in place). Thanks for digging that QA up though. Is there a way to appeal for rule changes in future years... (The way quick exhaust valves were finally made legal this year R77)?

[Jon Stratis]

I think the described "spring locking" would be ok, as there's no oil involved. The other type, with oil, probably not as FrankJ pointed out.

Personally, I don't see them changing that in the future. Having a reservoir of oil on a robot really is only asking for trouble - a good impact or two and the thing splits open, releasing oil over your robot, other robots, and the field - can you imagine trying to get that cleaned up out of the field carpet so it doesn't impact future matches?

Your best bet at getting anything legalized in the future, I think, is to keep asking questions about it on the Q&A each year. Carefully think through the consequences to the field, other robots, and general safety and of ways rules could we written to mitigate those consequences, without requiring a significant amount of engineering from teams - for example, see R69.

[nuclearnerd]

Originally Posted by Jon Stratis

Having a reservoir of oil on a robot really is only asking for trouble - a good impact or two and the thing splits open, releasing oil over your robot, other robots, and the field - can you imagine trying to get that cleaned up out of the field carpet so it doesn't impact future matches?

A burst gas spring would be very bad, whether or not there is any oil present. these things store nitrogen at more than 1000 psi - any damage would make for a pretty scary bang! Does the oil lock make the risk of failure greater? What if we could prove (by manufacturer testing for instance) that the locking valve would fail under pressure before the cylinder did, protecting the integrity of the housing?

(these are hypotheticals of course. If the QA were open, I'd direct these questions to the GDC)

[EricH]

The other method would be to email frcteams (at) firstinspires.org with question, suggestion, and/or "what would it take to have these considered legal".

[GeeTwo]

FIRST takes both safety and inspectability by crews who don't quite know what they're looking at seriously. If you want to propose such a rule to FIRST, I suggest trying to craft a rule that both ensures safety and is inspectable by FRC inspectors at the current base level. If you can't meet both criteria with the same rule, the chances of adoption go way down.

[FrankJ]

Although it is clear that First does monitor CD, Erich's suggestion is the official path for rules change suggestion per numerous mentions in the Q&A. I think the Q&A response was poorly thought out. Poor definitions make the RI's job difficult and leads to different inspectors making different decisions. Shock absorbers use oil. Most COTS "Gas springs" use more than an minuscule amount of oil. Here is a CD discussion on the Q&A.

In either case you are far more likely to pretzel the rod than to rupture the cylinder.

[nuclearnerd]

Originally Posted by FrankJ

In either case you are far more likely to pretzel the rod than to rupture the cylinder.

To wit, here's the response from Bansbach I received today. The short answer is in most types the lock will fail before the cylinder, and a safety overload release can be specified:

In general terms the following describes the different locking springs

For K locking gas springs, if you exceed the locking force in compression, the valve will open and the gas spring will compress. Please note however that the valve will close back up if the force is removed and the spring will lock again.

For P locking, the same applies as the K locking but in the reverse directions. In this case, exceeding locking force in extension results in the valve opening

Please note however that in both cases, overloading the gas spring degrades the sealing mechanism of the spring and you may eventually have a failure where the unit no longer locks.

For KX locking, the force listed is the maximum force in both directions based on the material strength of the locking components. We advise you never exceed or plan to exceed the listed locking force in any of the gas springs as listed in our catalog.

Locking gas springs are not meant to function as shock absorbers.

If you need a gas spring that has a safety overload we can actually provide that as an integral part of the spring. We refer to this type of gas spring as a V-variation of the locking springs. For example, we can have a spring whose regular locking force is 1000N and if exceed will allow movement until the force drops back down.

As suggested, I will write an appeal sometime this summer and send it to FIRST HQ. In the meantime we'll unfortunately abandon this approach to modifying our robot for off-season events.

[AdamHeard]

I guess I'm missing something, how are these different in terms of the rules compared to the traditional gas springs teams have been using?

There was a QnA during season that confirmed they are legal even though they have a small amount of oil inside for lubrication and sealing.

[Jon Stratis]

Originally Posted by AdamHeard

I guess I'm missing something, how are these different in terms of the rules compared to the traditional gas springs teams have been using?

There was a QnA during season that confirmed they are legal even though they have a small amount of oil inside for lubrication and sealing.

Originally Posted by nuclearnerd

The other types put the valve in an oil reservoir, which locks the cylinder rigidly (in one direction or the other or both).

Adam, at issue is the "oil reservoir" some of them use - that is not a "minuscule amount for lubrication" as specified in the Q&A ruling.