Pic: would this chassis shape be legal?

[Creator Mat]

OK my team wants to do something like this (see attached pic) for our chassis shape. we follow the bumper rules. Would this type of shape be legal when herding the balls? I think it is legal because the ball would be free to move within the indentation area and thus would not be possession. I want to find out what the rest of the FIRST community thinks. Also if you think this would break a bumper rule or some other rule beyond just the no possession rule please say something.

Note: the red strip on the ledge thing on the top is supposed to be the bumpers

[cziggy343]

I do not think so. but i could be wrong. i think that would be considered inside the bumper zone too far.

[EricH]

Provided that 1) the ball doesn't go more than 3" into the frame (<G46>, <R19>) and that 2) there is no gap in the frame (bumper rules, definition of frame perimeter), yes.

Clarification of 2): Frame perimeter is defined as:

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 FRAMEPERIMETER, wrap a piece of string around the ROBOT at the level of the BUMPER ZONE - the string describes this polygon.

The applicable portions of <R07>, the bumper rule, are as follows:

Originally Posted by <R07>

A. BUMPERS must provide complete protection of the entire FRAME PERIMETER of the ROBOT (i.e. BUMPERS must wrap entirely around the ROBOT). The BUMPERS must be located entirely within the BUMPER ZONE when the ROBOT is standing normally on a flat floor, and must remain there (i.e. the BUMPERS must not be articulated or designed to move outside of the BUMPER ZONE).
...
I. BUMPERS must attach to the FRAME PERIMETER of the ROBOT with a rigid fastening system to form a tight, robust connection to the main structure/frame (e.g. not attached with Velcro). The attachment system must be designed to withstand vigorous game play – nut and bolt fasteners are recommended. All removable fasteners (e.g. bolts, locking pins, pip-pins, etc.) will be considered part of the BUMPERS.
...
M. The entire length of the BUMPER backing must be supported by the structure/frame of the ROBOT (i.e. the backing material must not be in “free space” between or beyond attachment points) (see Figure 8 – 3).

In other words, that gap in the frame/bumpers needs filling.

[keehun]

What I had thought was that the robot needs to be in a rectangular configuration (though I saw a hexagonal configuration in the manuals?)... In any case, the ball can't be "hogged" by a robot...

[Kevin Sevcik]

Not. Re-read the frame perimeter definition. If you wrap a piece of string around that frame, you have short diagonal bumpers on the corners and a bumper across your little U thing. All bumpers must be rigidly backed, and you don;t have backing behind either the diagonals, or the U.

[jamie_1930]

Originally Posted by Creator Mat

OK my team wants to do something like this (see attached pic) for our chassis shape. we follow the bumper rules. Would this type of shape be legal when herding the balls? I think it is legal because the ball would be free to move within the indentation area and thus would not be possession. I want to find out what the rest of the FIRST community thinks. Also if you think this would break a bumper rule or some other rule beyond just the no possession rule please say something.

Note: the red strip on the ledge thing on the top is supposed to be the bumpers

The problem stems from

<R19> ROBOTS must be designed so that in normal operation BALLS cannot extend more than 3 inches inside the FRAME PERIMETER below the level of the BUMPER ZONE.

We had this discussion today and came to the conclusion and the fact is that since the perimeter is defined as

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.

It means that there are restriction on how deep that cut can be where you plan to hold the ball.

See the diagram on page 14 of Section 8 of the game manual for more clarification, if needed.

[ssa3512]

Originally Posted by Creator Mat

I think it is legal because the ball would be free to move within the indentation area and thus would not be possession. I want to find out what the rest of the FIRST community thinks. Also if you think this would break a bumper rule or some other rule beyond just the no possession rule please say something.

I believe you misread the rule on "Possession" and are confusing with "Carrying"

<G43> ROBOT BALL POSSESSION - ROBOTS may POSSESS only one BALL at a time. Violation: PENALTY.
<G44> BALL CARRYING – ROBOTS may not CARRY BALLS. Violation: 2 PENALTIES for each CARRIED BALL.

Possession refers to keeping the ball in the same position relative to the robot when turning the robot, etc. The ball is still in contact to the floor. This is legal.
Carrying is where the ball is possessed by the robot AND off the surface of the floor. This is not legal.

The rule you need to worry about is as follows

<G46> BALL Penetration Restriction – The BALL must not extend more than 3 inches inside the FRAME PERIMETER as defined in Rule <R19>. Violation: PENALTY for a basic infraction, plus a YELLOW CARD if no immediate attempt to remedy.

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.

In your design, the FRAME PERIMETER is a rectangle, even though you have that indent on the one face of the robot. The ball would not be allowed to penetrate more than 3 inches into that rectangle. Hope this helps

[Karibou]

I don't believe so.

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

Originally Posted by <R07>

A. BUMPERS must provide complete protection of the entire FRAME PERIMETER of the ROBOT (i.e. BUMPERS must wrap entirely around the ROBOT). The BUMPERS must be located entirely within the BUMPER ZONE when the ROBOT is standing normally on a flat floor, and must remain there (i.e. the BUMPERS must not be articulated or designed to move outside of the BUMPER ZONE).

(emphasis mine)

[Trent B]

Kara, he could alter his design to have a cross bar near the top with bumpers but the hole idea sorta fails for this problem.

Frame Perimeter is the polygon made by string wrapped around (Robot Definitions)
R19 and G46 if it penetrates Frame Perimeter over 3" you get penalized.

As long as it fits in 3" or less it could work in which case your hole is probably too deep.

Number crunching time

9" Diameter Ball, 4.5" Radius Ball

http://en.wikipedia.org/wiki/Circular_segment

Using this page.

h=R(1-cos(theta/2)) thus 3=4.5-4.5cos(theta/2)
-1.5=-4.5cos theta/2
1/3=cos theta/2
arcos 1/3 =70.53 degrees = theta/2
Theta = 141.06 degrees

Now Find the length of the Chord
C=2Rsin(theta/2)
C=9 sin 70.53 degrees
C =8.89"

Using radians for precision as wolfram alpha gets a lot of them you get 8.5"
Now this is the line C in the wikipedia page and there is some space if you extended c to the tangent line perpedicular to it (the ground)

9-8.5 = .5 .5/2 = .25" on top and .25 below so you need a bar at 8.75" if not lower to stop the ball from going in over 3"

[gburlison]

Originally Posted by Creator Mat

OK my team wants to do something like this (see attached pic) for our chassis shape. we follow the bumper rules. Would this type of shape be legal when herding the balls? I think it is legal because the ball would be free to move within the indentation area and thus would not be possession. I want to find out what the rest of the FIRST community thinks. Also if you think this would break a bumper rule or some other rule beyond just the no possession rule please say something.

Note: the red strip on the ledge thing on the top is supposed to be the bumpers

I don't think this is legal. If you filled in the gap on the part of the frame at the height of the bumpers, it might be a legal frame, but the frame perimeter will include this filled in area and if a ball protrudes more than 3 inches inside this frame perimeter, you may not pass inspection and will incur a penalty if this happens during play.

[ralcony]

I am relatively new to FIRST competitions so maybe this is a silly question butm I thought in the webcast they changed the bumper color by removing a piece of elastic fabric. How could you keep have a break in the bumper and use the piece of fabric for quick alliance color changes?

[EricH]

Originally Posted by ralcony

I am relatively new to FIRST competitions so maybe this is a silly question butm I thought in the webcast they changed the bumper color by removing a piece of elastic fabric. How could you keep have a break in the bumper and use the piece of fabric for quick alliance color changes?

What they did was called out in <R12>. You can have the bumpers be one color, then have a cover in another color. Keep the restraints strong and hidden.

How exactly you do it is up to you.

[Chris is me]

I didn't interpret the wording of "BUMPERS must wrap entirely around the robot" as "BUMPERS need to cover every surface of the BUMPER PERIMETER". Otherwise, why would they specify the minimum six inch bumper length, and empahsize that every corner needs to be protected? Those rules would be completely redundant and unnecessary, unless they assume people were planning robots less than six inches long.

I took "entirely around the robot" to mean 12 inches of bumper on every side and generally as much around the robot as possible. I'll ask the Q&A of course as I'm in the minority obviously and am probably wrong, and will assume so from now on.

[engunneer]

The manual states

100% bumper coverage
fully backed up bumpers (touching frame)
6" bumper segment length
3" ball intrusion max

In short, the proposed design by the OP is not legal on many counts.

the 6" bumper segment length also applies to chamfered corners, not just length and width of the robot.

the robot bumper perimeter (shape of the frame) only has to fit inside the 28x38 rectangle, and follow all bumper rules. Everything else is up to you - hexagon? Octagon? Circle? random 5 sided shape? All legal.

[jonzjos]

I think this would be legal. Frame perimeter follows the same shape as a string. A shallow recess (3" deep) falls inside the perimeter. So this 3" recess is the only zone that you can do any work to the ball (kick, spin, grasp). Of course you can generally herd the ball by pushing it with the bot all you want.