legality of bolt and screw heads breaking plane of chassis meeting bumpers

[windell747]

Hi,

I should have thought of this earlier, but our robot design is such that our wheel brackets are flush against the surface of the chassis of our robot. To assemble the wheel brackets, we use 1/4-20 cap screws and 3/8" bolts and such. Our bumpers mount to the chassis such that the plywood is flat against the C-channel.

When the wheel brackets are mounted to the chassis, the heads of the bolts holding the wheel brackets together extend into the plane that is between the bumper plywood and the chassis. Is this going to cause a problem with the rules?

I really hope not...because only the bolt heads go through this plane. Even with the bolt heads, our robot (wo bumpers) is within the volume restrictions.

Thanks for your time!
windell

[Mike Martus]

There was an update regarding this issue... main concern here is that you can fit within the sizing box. The other issue is covered in the update.

[artdutra04]

Originally Posted by windell747

Hi,

I should have thought of this earlier, but our robot design is such that our wheel brackets are flush against the surface of the chassis of our robot. To assemble the wheel brackets, we use 1/4-20 cap screws and 3/8" bolts and such. Our bumpers mount to the chassis such that the plywood is flat against the C-channel.

When the wheel brackets are mounted to the chassis, the heads of the bolts holding the wheel brackets together extend into the plane that is between the bumper plywood and the chassis. Is this going to cause a problem with the rules?

I really hope not...because only the bolt heads go through this plane. Even with the bolt heads, our robot (wo bumpers) is within the volume restrictions.

Thanks for your time!
windell

According to the FRAME PERIMETER rules this year, these bolt heads will not be allowed. You will have to artificially inflate your frame perimeter (by gluing strips of wood, plastic, etc) around your chassis so the bolt heads that aren't within the BUMPER ZONE are within the FRAME PERIMETER.

It's a pretty dumb rule, but it is what it is. Hopefully it will be amended next year.

[Mike Betts]

Here is a picture I made for training my inspectors...

[rsisk]

Mike,

You should add one more element to your excellent picture

The wood backing of the bumper sits on top of the bolt head without any kind of indention. In other words, the bumper is not firmly backed by the frame.

<R07> 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).

[Coach Tom]

Judging from the many robot photos already posted, many teams have misinterpreted R16:

" During normal operation no part of the ROBOT shall extend outside the vertical projection of the FRAME PERIMETER, except as permitted by Rule <G30>.
a) Exception: To facilitate a tight, robust connection between the BUMPERS and the FRAME PERIMETER, minor protrusions such as bolt heads, fastener ends, rivets, etc that are excluded from the determination of the FRAME PERIMETER and are within the BUMPER ZONE are permitted."

I am afraid that teams read the "minor protrusions such as bolt heads, fasteners, ..." independent of the BUMPERS -- like last year's rule.

My guess is that 50% of the robots will arrive to week one events out of spec.

[Mr. Lim]

Okay, some responses in this thread are causing me to be confused. I thought this year fastener heads and small protrusions were NOT considered part of the FRAME PERIMETER as per the definition provided in Section 8, Page 4:

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.

Now my interpretation is that this means that bolt and screw heads are OK if they extend past the FRAME PERIMETER - regardless of whether they are within the bumper zone or outside of it (i.e, this exception is not limited to bolt heads and screw heads between 10" and 16" above ground level).

Why would I interpret this in this way?

1) Because the definition doesn't explicitly say the bolt head exclusion is limited the bumper zone area.

2) If the bolt head exclusion only applied to the bumper zone, robots with extended bolt heads above or below the bumper zone would just shim their frames to artificially extend the FRAME PERIMETER - exactly what Art Dutra suggested above - and completely counter to the intent of "encouraging a tight, robust connection between the BUMPERS and the FRAME PERIMETER."

However, these bolt heads and screw heads must STILL comply with the overall 36" x 28" maximum dimension. Meaning you might have bolt heads that stick out of your frame, but you still must FIT IN THE BOX.

[Joe Ross]

Originally Posted by Mr. Lim

Now my interpretation is that this means that bolt and screw heads are OK if they extend past the FRAME PERIMETER - regardless of whether they are within the bumper zone or outside of it (i.e, this exception is not limited to bolt heads and screw heads between 10" and 16" above ground level).

Why would I interpret this in this way?

1) Because the definition doesn't explicitly say the bolt head exclusion is limited the bumper zone area.

It says that the frame perimeter is defined inside the bumper zone (first sentence).

See also <R16>.

[Mr. Lim]

Originally Posted by Joe Ross

It says that the frame perimeter is defined inside the bumper zone (first sentence).

See also <R16>.

Thanks Joe, having one of those days...

And yes Coach Tom, you're probably right that many teams will show up with illegal robots - it looks like I'm a prime example of one of those people who were confused!

But to avoid sidetracking this thread, I'd like to know then if the OP's situation is in fact LEGAL assuming all extended bolt heads are within the bumper zone, and the bumpers have been counterbored to allow the bumper to sit flush against their frame.

[sgreco]

Ok, I'm a bit confused.


Frame Perimeter

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.

R-16

Exception: To facilitate a tight, robust connection between the BUMPERS and the FRAME PERIMETER, minor protrusions such as bolt heads, fastener ends, rivets, etc that are excluded from the determination of the FRAME PERIMETER and are within the BUMPER ZONE are permitted.

Note Under R-16

Note: This means no “mushroom-bots.” If a ROBOT is designed as intended, in normal operation you should be able to push the ROBOT (with BUMPERS removed) up against a vertical wall, and the FRAME PERIMETER will be the only point of contact with the wall.

These Three parts of the rules completely contradict each other.

The definition of frame perimeter is consistent with the first part of R-16, which would make bolts protruding perfectly legal.

The note under R -16 completely contradicts everything. I would be more inclined to believe that a part of rules would be more correct than a note underneathe, and I would also be more inclined to believe that something that appears in the rules twice would be more correct than a note that occurs once. Based on what I've seen and read I have no reason to believe that protruding bolts are illegal; true there is some gray area, but since two distinct sections say it is legal, I would think that I can fairly assume that it is legal.

To me the rules pretty clearly allow the bolts to protrude as neither of the first two quotes I posted have been removed from the rules.

[EricH]

Remember, notes are meant to clarify. They are not rules.

If the bolt and screw heads are in the bumper zone, you're fine. Just make sure the bumpers are pocketed to take the bolt heads.

If the bolt and screw heads are above or below the bumper zone, you're not fine and will have to either expand the frame perimeter or reduce the bolts' protrusion to zero.

[sgreco]

If in fact a robot had bolt head extending out of the frame perimeter, but inside the bumper zone, then when the bumpers were removed and the robot were pushed against a wall, the bolt head would hit the wall and not the frame perimeter, which would make this note not make sense.

Note: This means no “mushroom-bots.” If a ROBOT is designed as intended, in normal operation you should be able to push the ROBOT (with BUMPERS removed) up against a vertical wall, and the FRAME PERIMETER will be the only point of contact with the wall.

[Mr. Lim]

Originally Posted by sgreco

If in fact a robot had bolt head extending out of the frame perimeter, but inside the bumper zone, then when the bumpers were removed and the robot were pushed against a wall, the bolt head would hit the wall and not the frame perimeter, which would make this note not make sense.

I think the note was a good example in illustrating the general application of the FRAME PERIMETER, which was its original intent. It's not as good in illustrating the protruding bolt head exclusion, which was added later in a Team Update(?).

The note clarification does make more sense if you interpret that the protruding bolt heads in the bumper zone "simply disappear" because they are excluded from the FRAME PERIMETER. By magically pretending the excluded bolt heads no longer exist, your FRAME PERIMETER should be the first thing to touch a wall.

(That also means any protruding bolt heads above or below the bumper zone will cause a problem - they are NOT excluded, and still have to be taken into account in the example)

Kind of a weird assumption, and I've already shown in this thread that making assumptions is generally a bad idea. However if you do this, the scenario seems to better the reflect the actual rules as written.

[Al Skierkiewicz]

I know that this is a complicated area of the robot rules. You must look at all the rules and the bumpers must satisfy all the paragraphs in R07. Fasteners and bolt heads inside the bumper zone are permitted to extend beyond the FRAME PERIMETER and in R07, par D, holes and pockets are allowed to be made in the backs of the bumpers to facilitate secure mounting of the bumper system. In no configuration may any part of the robot exceed the maximum dimensions of R10 whether that be inside or outside the bumper zone. As pointed out above those fasteners in the BUMPER ZONE that project outside the FRAME PERIMETER are permitted. Similar fasteners projecting the same amount beyond the FRAME PERIMETER but outside the BUMPER ZONE are not permitted.

[sgreco]

I'm sorry to keep dwelling on this topic, but does anyone know the intent of this rule? What changed from last year to this year, or any other year that made this rule need to be changed?

I can't see anything harmful about having a bolt extend a little underneathe the bumpers. The only thing I can see is if they were sharp, but that is covered in R-04 and thus shouldn't make a difference in the determination of this rule.

(That said the rules are the rules and we have to follow them, I'm just curoius if anyone knows the intent)