Hello, the recent manual update has reworded SG14 to read “Once the Match begins, Robots may expand, but no horizontal dimension can exceed 36” (914.4 mm) at any point during the Match”.
I have discussed this with members of the community, but there exists an ambiguity in this wording that has led to confusion over what exactly “Horizontal dimension” is defined as.
There are two possible interpretations of “Horizontal dimension” -

A) Horizontal dimensions defined as all dimensions measured through each horizontal plane that slices through the robot.
OR
B) Horizontal dimensions defined as measured from the top down projection of the robot onto a single horizontal plane.

There is no standard definition of “Horizontal dimension”, but the combination of definitions for “horizontal” and “dimension” appears to agree with case A.
I have included an image below of the bounding boxes that could result from each interpretation of “horizontal dimension”

From definition A, the bounding box becomes that of an oblique cylinder. As shown by examining the image above, any horizontal plane that slices through the oblique cylinder will still contain no dimension greater than 36".
However, from definition B, a top down projection of an oblique cylinder would exceed 36", making the only viable bounding box the right circular cylinder in the above image.

So which definition of “Horizontal Dimension” does In The Zone use?
And if it is case B, (which it appears is the only definition that satisfies the intent of the rule) then why was it reworded if it is still bound by a cylinder with a diameter of 36" and infinite height as this is the only possible max bounding box that could satisfy case B?
I would like to petition that SG14 and VUG7 to be changed in the manual to remove this ambiguity and reflect your answer presented here.

We apologize for any ambiguity or confusion that the update may have introduced - this was definitely not our intent. The update was aimed at making robot design and enforcement more straightforward. The short answer is that your case B is correct, not case A. For the long answer, allow us to explain our rationale a bit further.

Yes, a cylinder with infinite height makes sense for robot expansion theoretically and in CAD. However, after further review and feedback, we determined that it was not practically enforceable in the VEX Robotics Competition.

By making the maximum dimension a “point-to-point” width, rather than a true cylinder, it can be easily visually estimated using a standard yardstick or the diagonal of a standard VRC field tile (which is roughly 34"). The new Robot Expansion Sizing Tool that will be used by Event Partners this year is a “maximum width” tool, as seen here. Using this tool, there are some fringe cases (non-round shapes of constant width) that would not technically fit within a cylinder, but would still appear legal. See the image attached to this post for one example.

Ultimately, you are correct - a cylinder and a shape with “maximum horizontal dimension” are very similar. Thus, we feel that the majority of robot designs will not be affected by this change. However, the consistency with which robot expansion can be judged is now much more guaranteed. One of the primary goals of the Game Design Committee is always to ensure a consistent and fair experience for all teams involved in competition, and we believe that the revised expansion rule accomplishes that goal much more effectively than the original.

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