Bumper Wall Attachment

[aldaeron]

Hi all,

Just wanted to get a second opinion to make sure we don't show up at inspection and have this wrong. The attached image shows some angle aluminum that would be used to mount the bumper wall to the frame. It also show fastener heads off the back of the recommended aluminum angle used to hold on the cloth. Are these both legal per R-7N?

Also - I was curious if it was better to use angle as shown in green or use the Tee nuts that they show in the manual. This is my first year doing FIRST and I wanted to make sure this is a very robust connection.

Thanks!

[EricH]

Looks OK. The fastener heads will probably count towards bumper weight, but you almost have to try to get a 15# bumper, let alone a 20# one.

The tight and robust connection called for is up to you. If, for example, you fastened through the angle to the top of a frame member, that would most likely be a good connection, unless you did something wrong.

[The Megan 2207]

I'm not sure why you're specifically referencing <R07-N>, as this part of the rule only deals with how far the "hard" or "soft" parts of the bumper can extend from the frame perimeter.

My team has used a very similar angle attachment method for the past few years, but instead of attaching the angle to the bumper, we attach it to the robot and attach the bumpers by bolting through the angle. We find this is easier than trying to blindly attach the bumpers through the c-channel kitbot frame (we usually use that for our chassis).

From my understanding of the bumper rules, a protruding bolt head is perfectly legal, as it would only extend under your robot's frame. We normally just use wood screws to hold the angle in place, and we've never had a problem with that.

[JB987]

Your question is a good one that many would benefit from knowing an official answer to. Why not direct it (with included image) to the Q and A forum to establish a "legal" interpretation we may cite should an inspector have a different interpretation?

[aldaeron]

I forgot to draw the FRAME PERIMETER. Is it the red line or the black line in the new picture?

[Wayne Doenges]

Is it the red line or the black line in the new picture?

Red Line

[aldaeron]

Much obliged. That is what I thought, but I didn't want to get it wrong. There are a lot of nuances to all the rules and I don't want to be wrong.

[GaryVoshol]

You would want to be sure that any protrusions on the back of the bumper board don't interfere with a tight robust fit of your bumper to the frame.
Wood to frame = good
Bolthead to frame = bad, because of small contact area

[aldaeron]

I am trying to get an opinion on which of these options has worked better in the past. The light blue square is the box beam from the chassis.

[GaryVoshol]

Originally Posted by aldaeron

I am trying to get an opinion on which of these options has worked better in the past. The light blue square is the box beam from the chassis.

Of the two examples, the second is a more robust connection. The frame member is in the middle of the backer board. The one with the frame at the bottom of the board will have much greater forces on the connectors when it gets hit at the top of the bumper.

AndyMark sells some bumper kits, and you can see how pairs of the brackets used here: http://store.andymark.biz/am-0325.html
To see how the brackets work, look at the pdf link "Bumper Segment Example Layout" on that page.

They also sell c-channel brackets: http://store.andymark.biz/am-0317.html

Originally Posted by aldaeron

In the left design, would the green piece of angle count as part of the robot? I was planning to attach it with wood screws (the horizontal black screw looking thing) meaning it would not be meant to be removed. Then I would use bolts (the vertical black screw looking thing) to attach to tapped holes in the frame.

To me that seems like it falls under part G and I and therefore the weight counts as the bumper weight not the robot weight.

Al's the inspector, not I, but in my opinion if the brackets remain attached to the bumper, they are weighed with the bumper, as is the connector bolt or pin.

By the way, for anyone still reading, this is an example of a good way to ask questions. aldaeron did some research, drew diagrams, referenced the rules, and asked for confirmation. Much better than a terse "How do you think I should attach my bumpers?" query. Rep given.

[Al Skierkiewicz]

aldaeron,
The test we make when looking at the robot and bumpers involves a determination if the team is shifting robot weight to the bumper attachments. Our guide is the highlighted rule about bumper attachment structure and par J. Although you do not show the frame in your drawing, I am guessing it still exists at the top and bottom of the bumper. I ask in order to insure you have met with par M

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).

By now most teams are asking "why?" on the entire bumper section. This has been a evolution of rules making by the GDC to protect robots throughout the season. The success of this endeavor was evident in last year's competition and the lack of serious robot damage due to collisions with the field, trailers and other robots. Inspections are more difficult but the effect is better for all.

[Tristan Lall]

Under current rules (this wasn't true in 2008, for example), if the bumper bracket is not intended to be removed from the bumper, it counts toward the bumper weight and not the robot weight. (Note that in the case where the bumper bracket is both removable and structural with regard to the robot, and still serves as a fastening method for the bumper, you may encounter an inspector who instead interprets your design as a not-quick-enough bumper removal method—wood screws—and a robot structural member that happens to be removable. You may have to discuss your intent with him, and see if he agrees with your interpretation—there's a good chance that you'll receive the benefit of the doubt.)

Also note that if your wood screws (attaching the clamping angle) protrude from the bumper, you need to consider whether they lie on the frame perimeter, or whether the angle or plywood lie on the frame perimeter instead. By <R07I>, "BUMPERS must attach to the FRAME PERIMETER" (not the clearest directive, given what the frame perimeter is), but there's apparently no prohibition on penetrating the frame perimeter to do things other than attach.

You may also want to ask the Q&A about the 1 in limit of hard parts (measured from the frame perimeter). It appears that it doesn't apply in the inward direction (though the existing question and answer dealing with that might both have been clearer). This has significant implications for the design of "multi-part attachment systems".

[joek]

Originally Posted by aldaeron

Hi all,

Just wanted to get a second opinion to make sure we don't show up at inspection and have this wrong. The attached image shows some angle aluminum that would be used to mount the bumper wall to the frame. It also show fastener heads off the back of the recommended aluminum angle used to hold on the cloth. Are these both legal per R-7N?

Also - I was curious if it was better to use angle as shown in green or use the Tee nuts that they show in the manual. This is my first year doing FIRST and I wanted to make sure this is a very robust connection.

Thanks!

we used angle brackets last year and they work great

[martinswat1806]

What we have learned, and it all depends on the design of your robot, is to put a rectangle tube of aluminum on the back side of the bumper that fits into a slot on the frame of your robot then you just drill a hole from top to bottom and pin it in place using a long bolt. Hope it helps.

[Al Skierkiewicz]

aldaeron,
I just want you to be sure as I was a little confused when I first looked at your post. The angle aluminum shown in the bumper drawing is to secure the cloth covering to the plywood backing. It is not the attachment but is merely clamping the cloth in place. In the drawing, the bolt threaded into the blind nut is the attachment.
The drawings you submitted are both used by teams but the one using the additional angle is sometimes more easy to remove. However, the support angle is generally weighed as part of the robot.
From <R07>

G. Each set of BUMPERS (including any fasteners and/or structures that attach them to the ROBOT) must weigh no more than 20 pounds.
H. BUMPERS must be designed for quick and easy installation and removal, to aid in weighing and inspection (as a guideline, BUMPERS should be removable by one person in less than ten minutes).
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.
J. If a multi-part attachment system is utilized (e.g. interlocking brackets on the ROBOT and the BUMPER), then the elements permanently attached to the ROBOT will be considered part of the ROBOT, and the elements attached to the BUMPERS will be considered part of the BUMPER. Each element must satisfy all applicable rules for the relevant system.