Bumpers

[Hellfeier675]

My team has been trying to figure this year's bumper rules out. We have seen the pictures in the manual saying that you can't have bumpers cross a huge gap in your robot, but it doesn't say that we have to have bumpers all the way around our robot like last year either.

Does this mean that it is ok to have a cut-away in the robot chassis and have it not be covered by bumpers? Technically our whole frame perimeter is covered (the string around your robot test) Or does our entire robot have to be covered all the way around this year?

[Hellfeier675]

An example of what I mean can be found here.


http://www.chiefdelphi.com/media/photos/36641?

[notmattlythgoe]

BUMPER PERIMETER – the polygon defined by the outer-most set of exterior vertices of the
BUMPERS when they are attached to the HOSTBOT. (To identify the BUMPER PERIMETER,
wrap a string around the BUMPERS at the level of the BUMPER ZONE - the string describes the
polygon.)

BUMPERS must provide complete protection of the entire FRAME PERIMETER of the
ROBOT (i.e. BUMPERS must wrap entirely around the ROBOT). As part of the 100%
coverage, BUMPERS must protect all exterior corners of the FRAME PERIMETER. For
adequate protection, a full segment of BUMPER must be placed on each side of the corner
(see Figure 3-2).

Those right there answer the question. They must cover the entire perimeter.

[Hellfeier675]

Thank you, but that raises the question, if we have bumpers on all sides, then we are covering the whole bumper perimeter and have bumpers on all corners, however we still have a gap that isn't breaking rules cause it's not a gap larger than 8 inches covered by bumpers.

[notmattlythgoe]

The BUMPER backing must be supported by the structure/frame of the ROBOT (i.e. the
gap between the backing material and the frame must not be greater than 1/4” and no
section of BUMPER greater than 8” may be unsupported). See Figure 3-3.

This states the rules on the gaps BEHIND bumpers. You cann't have holes in your bumpers, but you may have a gap BEHIND the bumpers that is up to 8 inches.

[Nuttyman54]

Originally Posted by Hellfeier675

Thank you, but that raises the question, if we have bumpers on all sides, then we are covering the whole bumper perimeter and have bumpers on all corners, however we still have a gap that isn't breaking rules cause it's not a gap larger than 8 inches covered by bumpers.

The wording of the rule can be confusing. The FRAME PERIMETER and therefore the BUMPER PERIMETER is defined by the outermost set of vertices. In the example you provided, those would be the four outer corners of the robot. The FRAME PERIMETER does NOT include the two corners set back in the frame cutout, because those are not the outermost vertices.

Therefore, when you perform the string test, you get a rectangular loop of string which wraps around the four corners of the robot, and does not protrude into the cutout. It's a very long-winded way of saying you can't have part of your bumper perimeter which is concave.

With the string test above, you can see that the string goes across the gap, and therefore represents part of your BUMPER PERIMETER which does not have support for bumpers, and is illegal per rule <R07> K.

The rule is functionally identical to last year's bumper rules.

[Chris is me]

Originally Posted by Hellfeier675

but it doesn't say that we have to have bumpers all the way around our robot like last year either.

It absolutely says that. This has been known and discussed for weeks, and teams have been designing around it all year.

The entire FRAME PERIMETER doesn't have to be supported, but the entire FRAME PERIMETER must be covered by bumpers.

[Hellfeier675]

Our frame perimeter is covered bumpers.

Frame Perimeter: Wrap a piece of string around your robot at the level of the bumper zone, the string describes the polygon.

We would argue that having a recess in our frame, because the string does not touch that recessed frame member, that recessed frame member does not have to be covered by bumper.

We aren also basing this judgement off of past bumper rules, being that we only had to cover this bumper perimeter. These definitions are exactly the same as earlier years, and this year's height is identical to the height in the 2008-2009 definitions.

[notmattlythgoe]

Frame Perimeter: Wrap a piece of string around your robot at the level of the bumper zone, the string describes the polygon.

But when you pull the string tight you will have a rectangular shape, not a C shape.

[Hellfeier675]

But the rules are worded exactly the same as every other year, in which we were allowed to have a gap in the bumpers if there was a cut away in the robot.

[notmattlythgoe]

Except for the fact that this year it says 100%. The previous year it had a different percentage.

[Chris is me]

Originally Posted by Hellfeier675

But the rules are worded exactly the same as every other year, in which we were allowed to have a gap in the bumpers if there was a cut away in the robot.

This isn't true - rules were specifically written to allow part of the FRAME PERIMETER to be uncovered.

The entire "rubber band / string" of the FRAME PERIMETER must be covered, even if not all of the FRAME PERIMETER is backed by a structural member.

[Hellfeier675]

We just looked up the past rules and they are written exactly the same.

[notmattlythgoe]

BUMPERS must protect a minimum of 2/3 of the BUMPER PERIMETER. Teams are
encouraged to maximize the area of the ROBOT protected by BUMPERS. But up to 1/3 of
the BUMPER PERIMETER may be unprotected to provide flexibility in design options.

That was the difference in past years.

[Chris is me]

Originally Posted by Hellfeier675

We just looked up the past rules and they are written exactly the same.

The 2010 rule is the same, because it required bumpers around 100% of the robot.

The 2009 rule has this very notable difference:

Originally Posted by <R08-K>

BUMPERS must protect a minimum of 2/3 of the BUMPER PERIMETER.

Contrast this with the 2011 and 2010 manuals, which say 100% coverage multiple times.