Quote:
Originally Posted by Al Skierkiewicz
Tristan,
I am confused by your response, the FRAME PERIMETER is a series of planes, that are essentially perpendicular to the floor when the robot is in the Starting Configuration. As such, the backing of the bumper system that is mounted on the FRAME PERIMETER must also be perpendicular to the floor. There is no occasion where any part of the bumper system can be skewed or angled with respect to the plane(s) of the FRAME PERIMETER. The FRAME PERIMETER is determined by the outer most section of the Frame as determined by string test in the bumper zone. Once the FRAME PERIMETER has been established, it can be measured and the bumper system can be inspected. It is not possible to meet the rules with respect to bumper mounting (i.e. backed by frame with no gap greater than 1/4" be wider than 8" and supported at the ends by at least 1/2") on a skew polygon unless said polygon was skewed vertically by 1/4" or less in the bumper zone.
|
The frame perimeter definition refers specifically to a polygon, not to a series of planes:
Quote:
|
Originally Posted by Section 6.1
FRAME PERIMETER: 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.
Note: to permit a simplified definition of the FRAME PERIMETER and encourage a tight, robust connection between the BUMPERS and the FRAME PERIMETER, minor protrusions such as bolt heads, fastener ends, rivets, etc. are excluded from the determination of the FRAME PERIMETER.
|
Perhaps the series of planes to which you refer is the "vertical projection of the FRAME PERIMETER" (although that could include curved segments which are not strictly planar):
Quote:
|
Originally Posted by Section 6.1
STARTING CONFIGURATION: The physical configuration and orientation of the ROBOT when the MATCH is started. This is the state of the ROBOT immediately before being Enabled by the Field Management System, before the ROBOT takes any actions, deploys any MECHANISMS, or moves away from the starting location. This configuration is static, and does not change during a single MATCH (although it may change from MATCH to MATCH). In the STARTING CONFIGURATION, no part of the ROBOT may extend outside the vertical projection of the FRAME PERIMETER, with the exception of minor protrusions such as bolt heads, fastener ends, rivets, etc.
If a ROBOT is designed as intended and pushed up against a vertical wall (in STARTING CONFIGURATION and with BUMPERS removed), only the FRAME PERIMETER (or minor protrusions) will be in contact with the wall.
|
Since the bumper rules refer to the frame perimeter, but not to its vertical projection, I have to assume that they should be evaluated with reference to that polygon (whether it be rectilinear or curvilinear, and planar or skew
1).
To expand on what I'm talking about, consider a robot with four sides, each with an outermost edge running the whole length of the side within the bumper zone (i.e. the major protrusions relevant to the frame perimeter). If in the starting & playing configurations, the left and right edges are at 9.5 in from the floor, and the front and back edges are 2.5 in from the floor, there's no
planar polygon that can satisfy the string test. I'm skeptical that FIRST means for that robot to be illegal, and the only way to maintain any measure of fidelity to both the rules and geometry is to allow a skew polygon—i.e. a figure composed of segments that do not necessarily lie in a plane.
That's the "skew" to which I refer, but when I speak of "twist" I mean something else. When I describe a twisted bumper, I conceive of one in which the backing material is bent out of the vertical plane. I argue that if the bottom edge of the bumper backing lies on the frame perimeter polygon, and the top edge lies inside of it, then R21 is satisfied,
except—depending on interpretation—for the part about the vertical cross-section (including figure 4-8).
Now, as for the vertical cross-section, R22's blue box offers a suggestion about how to interpret figure 4-8 in a different context:
Quote:
|
Originally Posted by R22
BUMPERS must be located entirely within the BUMPER ZONE, which is between two (2) and ten (10) in. from the floor, in reference to the ROBOT standing normally on a flat floor.
There is no explicit requirement that BUMPERS be perfectly parallel to the floor, however the requirement that BUMPERS be constructed per Figure 4-8, the vertical cross-section, does implicitly mean that a BUMPER should not overtly deviate from this orientation.
|
I think it's fair to apply the reasoning found there to R21, even though the blue box is attached to R22. After all, they're referencing the same figure and FIRST has never given any indication that they mean for a distinction to exist. The Q&A seems to be consistent with that interpretation of the constraints imposed by R21.
But note the distinction between "may not go inside the FRAME PERIMETER (see Figure 4-5)" and "should not overtly deviate from [vertical]". Figure 4-5 does not establish any constraint upon verticality (or flatness, for that matter). If they meant instead to refer to figure 4-8, and we interpret it as above, we're still left with a question of how much deviation is overt. That's why I express concern about consistency of enforcement: if it's 10° at one event, and then 2° at another event, we might have a bit of a problem.
Finally, "may not go inside" is phrased very strongly (compare "should not overtly deviate"), and this is an impossible constraint if there's any twist at all—as one might expect in a real physical part. I therefore contend that the Q&A is probably wrong in that respect, because we can't reasonably presume an intent to impose a practically impossible constraint upon a mandatory feature. Accordingly, I fall back on the necessity for officials to judge overt deviation.
1 To avoid skew polygons (and other issues), I've previously suggested that the frame perimeter definition could be improved if it were based upon the convex figure formed by the projection of the outermost extents of the robot (within the bumper zone) on to the floor, in the starting configuration.