I have gone through both the game manual, the admin manual, and the Q and A, and cannot seem to find how the 15 inch extensions will be measured. This is important for us because we have a arm that moves extremely quickly and we will not be able to measure it in its longest state.
I don’t imagine there would be documentation for that, as it’s usually “inspector’s discretion” or varies by region. You’ll likely need to make an easy and safe way to verify the length during inspection, likely just using a tape measure.
More details on your mechanism might help give a more specific answer.
This is a 15" extension from your frame perimeter in any direction. Look at the footprint to ensure its not past that. You can have more than one appendage extending past your frame perimeter at any given time.
If you have an appendage that can extend past it, you will have to demonstrate that it will not exceed that in a real match.
An arm extending outside the frame perimeter is usually measured by your inspector during inspection. They will typically ask you to extend it to it’s longest position and measure it there. If your arm is physically capable of extending over the 15", you will likely be asked to demonstrate whatever controls (software or otherwise) you have in place to ensure it stays in a legal state during a match.
You will need to be able to extend the arm to it’s full extension outside the frame perimeter during inspection, and the inspector will measure it at that point (personally, I like to use a tape measure on the floor with a plumb bob to make sure I’m looking straight, when it’s anywhere near close). As others said, being physically capable of further extension isn’t illegal, so long as you never go that far. But your inspectors will want to see the safeguards that keep it legal in cooperation so they can tell the refs what to look for in the field so they know when it is operating legally.
This question is relevant to an idea we’re discussing too.
We plan to design an extending mechanism to put a hook on the climbing bar and that mechanism lays-down along the length of our robot. It will be ‘stood up’ at the end of the match and extended, could be using a spring or maybe a surgical tubing. So the instant it starts ‘standing up’, it would likely start extending.
It will be 75 + inches tall with the hook when it’s vertical, but that 70-something inches will occur at some time, at some angle while it’s moving to vertical.
So we run the risk of being outside the 15 inches for just a short while–fractions of a second really. Robot is about 35" long and adding 15" means as long as it doesn’t break 50 inches horizontal, and 60 inches when at 20 degrees and 65 inches by 45 degrees…
I hope everyone can understand what I’m explaining here…
My gut feel is such an extension, no matter how fleeting, would be a rule violation. Is it?
yes, it is, no matter how brief. You’ll want to make sure there’s a way to prove it remains completely legal the entire time it’s extending/standing up (not just math, but Physical proof), and make sure it’s both clear and repeatable that it’s legal. The inspectors will want to take a close look at it, and they’ll tell the refs “it’s ok so long as it moves like this…”. That conversation will most likely happen while you’re on the field so the head ref can be watching you extend while the LRI is telling him it’s legal.
Breaking a rule for a fraction of a second is still breaking the rule, yes. It’s somewhat less likely to get called, of course.
If I were an inspector and I wanted some assurance that the controls on a mechanism were keeping it legal, I’d place the robot with the frame perimeter 15" from a wall and ask the team to actuate the mechanism. This is also a useful way to test such a mechanism yourself. If you hit the wall, you need to look at better ways to control your deployment.
In your case, you might have a pin that restrains the extension part of your mechanism that gets pulled out once the mechanism is at a tall enough angle that it can’t break the 15".
http://i.imgur.com/SLrE6HR.png
Hopefully that answers your question.
But maybe you’re asking how its assesed during inspection or a match? But it doesn’t matter how its assesed as long as you aren’t breaking the rule.
You should manually run that arm through its motion to see if it ever breaks the 15" rule. If something breaches that extra perimeter at any point, you need to fix that. Put in a physical stop, shorten it, whatever you need to do.
If your robot relys on breaking a rule to operate properly, it won’t see the field. The question is not will they notice, its how do I fix it?
Of course, you are assuming the wall sits at an exact 90 degrees relative to the floor 
Well no, they don’t usually. But they’re usually close enough for most purposes. I mean, if you have a 6WD with a center drop, then the frame isn’t going to be properly parallel to the ground either. Which is a fun thing to consider. Frame perimeter is defined relative to how the bot “normally” rests on the ground, but what does that mean if it rocks?
It means the teams, in collusion with the GDC, are trying to make life difficult for us poor inspectors!