# Question on 3 inch perimeter rule

I have been wondering how the word perimeter will be interpreted. I would like to know if you could build a u shape robot that the ball could go into the center as long as they did not invade over 3 inches in the robots actual perimeter. I was also wondering if they would interpret it a the larest square the robot can sit in. I also would like ot know if you have wheels out side the frame do they count? any help would be very apprieciated!!! thanks:)

they define it pretty well, and give an example. If you wrap a string around the robot then the string describes the perimeter.

String goes across U shaped openings, so the perimeter also goes across the opening, not into the U.

Last I remember from the rules, the perimeter is defined as taking a piece of string and wrapping it around the robot.

So it is basically the smallest square the robot could fit in (assuming your robot is square and not a different shape all together)

EDIT: beat againâŚ Iâll get it next time!!! runs off

FRAME PERIMETER â the polygon defined by the outer-most set of exterior vertices on the ROBOT (without the BUMPERS attached) that are within the BUMPER ZONE. To determine the FRAME PERIMETER, wrap a piece of string around the ROBOT at the level of the BUMPER ZONE - the string describes this polygon.
Sorry, but itâs the frame perimeter that is important.

If you have wheels in the bumper zone, Iâd guess theyâd be some of the biggest in FRC historyâŚ

BUMPER ZONE â the volume contained between two virtual horizontal planes, ten inches above the floor and sixteen inches above the floor.

If the U is deeper than 3" it would not be legal.

I would have to argue from a geometric point of view the the string would not merely cross the opening of the âUâ however loop around inside and measure the âperimeterâ. This is our first year participating and we are new to first so this may be something that has been recognized or acknowledged in the past, however I believe the âstring around the robotâ idea is just a basic concept that covers most generic robot shapes. The manual give this definition for the bumper perimeter: âBUMPER PERIMETER â the polygon defined by the outer-most set of exterior vertices of the BUMPERS when they are attached to the ROBOTâ. The frame perimeter is defined as such: âFRAME PERIMETER â the polygon defined by the outer-most set of exterior vertices on the ROBOTâ. While it does go on to talk about the string, they give an exact definition for each, which further convinces me that the string is no more than a concept. I am not interesting in starting a fight, however this seems like a debatable point which is of interest to me.

Emphasis mine.

These words indicate that the string does not loop in a crevice or space in the robot but travels from exterior point to exterior point, making a general shape of the robot.

Yep, and because it is âexterior verticesâ, the inner U is not part of the frame perimeter, because it has 4 vertices: 2 are exterior (at the front of the robot) and 2 are interior (the inner side of the U).

One method that weâve been using to describe this is instead of string, use a rubber band. Wrap it around the robot (in your mindâthatâs a huge rubber band!) in the bumper zone. Follow the rubber band; thatâs your frame perimeter.

As for the string being able to be pulled into the U, I believe they meant to say, âwrap a string tightly around the robot at the level of the bumper zoneâ.

As you guys are rookies, you probably donât know about the massive debates we had last year about what was and wasnât a legal bumper configuration. It was so bad that at one point someone posted a legal configuration and the comment was made that they couldnât do that because then weâd have nothing to talk about. Look it up and see just how discussed it wasâitâll be informative at worst and enlightening at best.

ahh, thanks to both of you for clearing that up (before we had to debate it on the team). You would think the perimeter would be the geometric perimeter but I guess this is one of many things weâll have to learn. Cheers for the advice!

no problemâŚ I remember how much trouble the âperimeterâ was last yearâŚ would hate to start it up again

thanks for the help! have a great FRC season!

All of this is really academic. It doesnât matter. The FRAME PERIMETER is defined at the BUMPER ZONE height, 10 to 16 inches off the ground. Thatâs above the ball. If you want an indent below the BUMPER ZONE to channel the ball, itâs perfectly legal. The ball will fit under your bumper.

If I understand you correctly I think you are mistaken.
step 1) define frame perimeter (e.g. using the string method)
step 2) ball may not enter more than 3" into frame perimeter, when viewed from the top. (i.e. may not enter more than 3" into the projection of the frame perimeter to any surface parallel to the floor)

The frame perimeter also projects downward onto the floor. This is the boundary which is used for both the 3" incursion rule and the 2 second âkicker zoneâ rule.

<R19> ROBOTS must be designed so that in normal operation BALLS cannot extend more than 3 inches inside the FRAME PERIMETER below the level of the BUMPER ZONE.
(emphasis mine)

But

<G46> BALL Penetration Restriction â The BALL must not extend more than 3 inches inside the FRAME PERIMETER as defined in Rule <R19>. Violation: PENALTY for a basic infraction, plus a YELLOW CARD if no immediate attempt to remedy.

They really should have repeated âbelow the BUMPER ZONEâ here, instead of just referencing <R19>.

Nevertheless, this is the way it has to be interpreted. Else, whenever an airborne ball went above your robot, youâd be in violation.

Yup. thanks for the correction!