I will attempt to provide some answers and hopefully clarity here. The previous (2022) rule (R408-C) stated:
“use a stacked pair of approximately 2½ in. (nominal, ~63mm) round, petal, or hex “pool noodles” (solid or hollow) as the BUMPER cushion material (see Figure 9-7). All pool noodles used in a BUMPER set (e.g. red set of BUMPERS) may not be modified (with the exception of cutting to length or cutting to facilitate mating pool noodles at the corners as required by R409) or deformed and must be the same diameter, cross section, and density (e.g. all round hollow or all hex solid). Cushion material may extend up to 2½ in. (~63 mm) beyond the end of the plywood (see Figure 9-8). To assist in applying the fabric covering, soft fasteners may be used to attach the pool noodles to the wood backing, so long as the cross section in Figure 9-7 is not significantly altered (e.g. tape compressing the pool noodles).”
The addition of the +/-0.25” “tolerance” in 2023 is to place bounds on “approximately”. It has been observed that, over time, the manufacturing of 2-1/2” pool noodles have strayed beyond what was intended as “approximately” or “nominally”. In essence, pool noodle manufacturers are now frequently “cheating” by advertising pool noodles as 2.5” or 2-1/2” when they are not even “close”. A 2” pool noodle (20% off the advertised 2.5”) was not originally intended to be “approximately” 2.5”. It was not that the pool noodles that teams used in the past that were 2” or 2.1” or 2.125” were “legal”. It was that there was no bounds placed on “approximately” or “nominally” so that distinction was open to interpretation from event to event, RI to RI, LRI to LRI. By now placing the +/-0.25” tolerance, there is an objective criteria in the rule that can be met without subjectivity. The FRC community requested that the robot rules be examined and edited such that there was as little subjectivity as possible. Responding to that, this is one of the areas that was clarified. Further, LRIs are trained, like I stated in this post that RIs shouldn’t be having teams tear apart their BUMPERs to measure the diameter of the pool noodle inside. If teams now know that they need to use pool noodles that are 2.5” +/-0.25” (between 2.25” and 2.75”) then they know what is expected of them. Previously a team’s and RI’s only measure of expectation was “approximately” 2.5”. If a team is super concerned they could keep a scrap piece of the pool noodles they used in their pit to show an RI and for easy measurement so no BUMPER disassembly should ever be needed unless an actual issue is discovered and needs to be corrected.
As to why the cutoff is specifically at 0.25”, first consider that the primary intent of the pool noodles in the BUMPERS is to provide protection. For this to happen a few things need to be regulated. First, the pool noodles must be of enough cross-section to adequately cushion the impacts. Second, the pool noodles must align for noodle to noodle contact. The intent of the BUMPER ZONE is to define that noodle to noodle contact zone on all ROBOTS. The BUMPER ZONE has changed some over time:
Pre-2007 BUMPERS didn’t exist.
2007 – 2-1/2” to 8-1/2” (6” tall) (in 2007 BUMPERS were optional)
2008 – 2-1/2” to 8-1/2” (6” tall) (in 2008 BUMPERS first became required)
2009 – 1” – 7” (6” tall)
2010 – 10” and 16” (6” tall)
2011 – 1” – 7” (6” tall)
2012 – 2” – 10” (8” tall)
2013 – 2” – 10” (8” tall)
2014 – 2” – 10” (8” tall)
2015 – No BUMPERS
2016 – 4” – 12” (8” tall)
2017 – Floor (0”) – 7” (7” tall)
2018 – Floor (0”) – 7.5” (7.5” tall)
2019 – Floor (0”) – 7.5” (7.5” tall)
2020 – Floor (0”) – 7.5” (7.5” tall)
2021 – Floor (0”) – 7.5” (7.5” tall)
2022 – Floor (0”) – 7.5” (7.5” tall)
Note that the BUMPER ZONE has not always extended to the floor as it has in the most recent years. In years past, it was common for teams to get penalties for their BUMPERS being “too low” when their bumper covers or reversible bumper flaps became dislodged during the course of match play and were dragging around on the floor. Altering the BUMPER ZONE in 2017 mitigated that issue.
In all of the history of FRC BUMPERS, the rules always called for use of a stacked pair of 2-1/2 inch “pool noodles”. The word “approximately” was added in 2013. But always the height of the BUMPER ZONE was 6” to 8” tall. This BUMPER ZONE height is directly related to the diameter of the pool noodles as I will attempt to describe below.
Please note that the blue box under R408-C goes on to say:
“All pool noodles used on a ROBOT must be the same in order to maintain the desired interaction between ROBOTS in the cases of BUMPER-to-BUMPER contact. BUMPERS containing pool noodles of vastly different construction may cause a “ramp” effect when interacting with other BUMPERS. Minor noodle compression as a result of smoothing BUMPER fabric or rounding a FRAME PERIMETER corner is not considered deformed. Any compression beyond that, e.g. for the purposes of flattening the pool noodle, is deformation and a violation of C.”
Given the allowed variation in the height (most recently 7.5”) of the BUMPER ZONE, the concern is, as noted in the blue box, a “ramp effect” being created by allowing too small of pool noodles. If ROBOT A builds their BUMPERS with a pair of stacked 2” pool noodles and mounts them in their BUMPER ZONE from 0” to 4” from the floor and then collides with ROBOT B who builds their BUMPERS with a pair of stacked 2” pool noodles mounted to their FRAME PERIMETER at the top of their BUMPER ZONE such that they are now 3.5” to 7.5” from the floor how much noodle to noodle contact would there be? Effectively only about 0.5” along the length of the noodles in the “impact zone”. And those forces are likely to cause a “ramp effect” as the higher mounted BUMPERS “ride up” over the lower mounted BUMPERS. And given the minimal 6” BUMPER length, if two “corner BUMPERS” were to meet in such a way there would be practically no “cushion” effect. In practicality, no team mounts their BUMPERS directly touching the floor. It would cause other issues like traversing cable protectors or whatever. So if we adjusted the scenario above up by 1” for some ground clearance then the top of the top pool noodle on ROBOT A and the bottom of the lower pool noodle on ROBOT B now align with more like 1.5” instead of 0.5”. Adjust that now from 2.0” pool noodles to the minimum 2.25” pool noodles and you have 2” of “overlap” and nearly upper pool noodle directly impacting the lower pool noodle with far less “ramp effect”.
I certainly understand teams frustration with now being informed that they need to be prepared to source “legal” 2.5” +/-0.25” pool noodles. So much so, I am personally searching for “legal” pool noodles and ordering them and measuring them and publicly documenting my findings so others can be informed without having to incur expense just to learn from something I/we could mitigate with the sharing of some information in this thread. I also understand the frustration teams have when they show up to a competition having built their BUMPERS with “approximately” 2.5” pool noodles only to have a “negative” inspection experience by being told their definition of “approximately” didn’t match the RI/LRIs. I certainly also understand the frustration an RI or LRI has telling a team something like that when everyone only has a vague, less than objective measure of “approximately” to go on. Al and I can and certainly do train the LRIs to exercise good judgement as I described in this post. However, “good judgement” is apparently still subjective and is no substitute for a tape measure.
I continue to endeavor to advocate for teams in the robot rules when and where I can. I take full ownership of this change request and did so in light of the request for the robot rules to be objective not subjective. I mentor a team as well. We are all in the same boat. My team has to make sure our pool noodles are up to spec now as well rather than just hoping they are “approximately” ok. If this change turns out to cause more problems than it solved, I will be the first in line lobbying FIRST HQ next year to go back to the old subjective way of defining what a legal pool noodle is and what isn’t in 2024. I advocated for a bit wider tolerance but for this coming year, as Collin has already let everyone know, this is what the plan is.