http://usfirst.org/uploadedFiles/Team%20Update%208.pdf
All I can say is** Bumper Clarification!**
And Bill’s blog post on the topic has been made official. Sorry to those who were debating configurations, but you got your wish for clarification.
I guess a lot of what we’ve inferred and speculated is now written in stone. I’d like to see how many teams have to change designs because this update.
Thanks, Eric, for posting the update. BCR’s bumper design is good to go.
It’s nice that they issued a series of clarifications. I wonder if they were getting tired of the discussion, or just concerned that teams might get the wrong impression? (Or, in fairness, were they motivated independently?)
However, (isn’t there always a “however”?) the definitions of corner and curve presented there are inconsistent with conventional usage. Geometrically, a corner is analogous to a cusp in Cartesian geometry (a discontinuity in the radius of curvature), where the adjoining segments are not mutually tangent at their intersection. By contrast, a (smooth1) curve has a continuous radius of curvature function. Given these very standard definitions, it’s more than a little confusing to invent the fiction that a curve is a corner (or even a series of corners).
Now, I understand the reasoning: we’re looking at a curve as a series of segments, sort of like we do in calculus. But that’s an approximation of a mathematical construct. In math, it’s properly described as the limit of that relationship—which is most assuredly not piecewise for a smooth curve, but rather a continuous function. And in the physical world, infinitesimal segments lying along a curve do not accurately represent the microscopic structure of an object. Either way, it’s a poor approximation: a smooth curve is not actually a series of segments—to contend otherwise is like saying that because we can represent the Earth’s surface as flat on a map, we should assume that in law, the Earth is flat.
Even accepting the idea of a large number of small segments, consider that as the number of corners goes to infinity, the angle of the infinitesimal corners goes to 180°—this is a series of flat surfaces of infinitesimal length, with corners infinitely close to 180°. You might argue that 180 − ε is not really a corner, since it can’t be directly percieved as a corner to an astute observer (the test proposed and repeated by the Q&A).
But I guess we shouldn’t mathematician the rules.
And more importantly, since each flat surface has infinitesimal length, there’s no way to stick a single 6 in segment of bumper on it. If you’re using the many-segments definition of a curve, there’s nothing within the rules that would relieve you from the minimum segment length requirement. So you must accept that a single segment of bumper can span multiple facets of the bumper perimeter, as would be necessary to allow curves made of infinitesimal segments. It would follow, then, that you could also bend a 6 in piece of plywood2 around any other corner (90° or otherwise), leaving 3 in on either side? But, no, the Q&A has ruled against this scenario as well.
And then, even if you accept the idea that you can bend the bumpers around these infinitesimal faces with a single segment, there’s still the problem of the statement that a curve must be “flanked by two six-inch [or longer3] segments of straight bumper”. All of the “corners” within the curve don’t need two adjacent segments of bumper (and couldn’t have them, because the faces are infinitesimally long)—what makes the tangent points (or the nearest “corners”) different? Why do these ones need to be flanked by separate segments, and not the others within the curve?
For so many reasons, this small portion of the update is hugely flawed.
What does this all mean, practically speaking? The update titles this section a clarification, and calls the bumper information guidance to inspectors—as distinct from a rule for teams to follow. While that’s great to know, I want to know what the enforceability of this is. Does FIRST intend for teams to be declared in violation of if they do not heed the “guidance that will be provided to the Robot Inspectors”? If it’s a rule, say it’s a rule—this was a perfect chance to just say so, plainly and clearly.
I’m a little disappointed with the way the bumper rule evolved over the course of the season so far. At the beginning of the year, I was quite happy to see the modifications to the bumper rule, which addressed a few major sticking points from previous seasons. But it looks like the desire to leave unchanged (the fact that it remains unamended was repeatedly mentioned in the Q&A forum and again in this update) has caused the window for a practical rule change to close. It’s now pretty late in the build season; frames and robots are nearing completion. It’s awful policy to spring a non-obvious interpretation like this on the teams at this late stage. Even if FIRST feels justified in defining corners and curves in the manner presented in this update, there’s a real need to consider whether the teams were also operating under the same definitions. Given that FIRST departs from mathematical convention in the update, I don’t see how it would be justified to assume that teams could have expected this interpretation.
There will be a small number of teams that will be forced to redesign their bumpers and frames at this stage, despite having followed the previous Q&A guidance and the rules. These were abundantly clear that there was nothing to prohibit curved bumpers, and provided a straightforward test to compare a curve and a corner. Given that at least one of these understandings appears rescinded (depending on your interpretation of the particulars of Update #8), FIRST may have subjected these teams to an unwarranted and potentially major inconvenience.
1Technically, even a piecewise function is a curve, so I clarify it with “smooth”, to put it into the proper context.
2I realize that bending plywood is difficult; that’s immaterial. Let’s say for argument’s sake that the team is using balsa plywood, or lots of steam and pressure.
3We can probably assume this.
I’ve said it before: instead of chewing on the rule and complaining that you don’t like the taste, just swallow it already and be done with it. It serves no constructive purpose to insist on reading the “guidance” with lawyerlike precision and finding ways to show it to be flawed. If, on the other hand, one accepts it as a given, it’s easy to find ways to justify its wording.
(For example, consider each of the infinite number of assumed corners on the curve. Recognize that a six-inch bumper segment is required on both sides of that corner. That automatically yields the description of a bumper covering the whole curve plus at least six inches of straight line on either side. Simultaneously recognizing that the assumed corner is nearly a straight line gets away from the problem of prohibiting “hard stuff” in the part of the corner between the sides.)
I’m a little disappointed with the way the bumper rule evolved over the course of the season so far.
Evolved? As you point out a sentence or so later, <R08> has not changed since the manual was first released.
Eric,
Be a little careful with those types of observations. The rules are the rules. The FIRST Q&A, Bills Blog, et cetera, are elaborations or clarifications or even pleas for rational thought but they do not change the rules.
Just clarifying what “official” is…
Regards,
Mike
I won’t speak for Eric, since he does a fine job on his own! But I don’t think he was saying that Bill’s blog was “official” - but that the subject of Bill’s blog regarding bumpers “Bumper Musings”](http://frcdirector.blogspot.com/2009/01/bumper-musings.html) had now been made official in Update #8!
Steve is correct. I was referring to that post, and only that post, and only the content thereof. Because that post was copied into a Team Update, it is now official and should be treated as such. No other post has this distinction at this time. (Note: That particular post had already been referenced by Q&A multiple times. That doesn’t make it official.)