The age old question - bumper mounting

[bachster]

Originally Posted by Dave McLaughlin

For the last few seasons 1983 has recessed our bumper backing into the frame and then pop riveted through the top and bottom to secure it. We think that the end result is not only aesthetically clean, but it adds to the structure of the frame. The recess is created by extending the upper and lower sheer panels past the vertical walls of the frame. If you look closely you can see the thru holes for the rivets in the attached picture.

http://team1983.files.wordpress.com/.../wp_001144.jpg

Dave, this looks like a very slick way to attach bumpers, but my initial reaction is that it would be in violation of R21-F (must attach to the FRAME PERIMETER of the ROBOT ...) and/or R26 (BUMPERS must be supported by the structure/frame of the ROBOT (see Figure 4-10). To be considered supported, a minimum of ½ in. at each end of the BUMPER must be backed by the FRAME PERIMETER...)

Since your FRAME PERIMETER (definition copied below for reference) is the top/bottom horizontal plate, it seems your BUMPERS are backed by an interior part of the robot, not the FRAME PERIMETER. Alternately, if you intend to define your FRAME PERIMETER as the vertical face which backs the bumpers, then the robot is in violation of the STARTING CONFIGURATION requirement.

Can you (or any experienced inspectors) help me understand how this attachment method is legal?


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.

[dellagd]

We just attach them in some solid yet semi-removable way. We dont actually ever take them off in competition because we just use reversible fabric on the bumpers. SOOOO much easier to just pull some velcro and flip the fabric instead of taking the whole thing off. We actually just did it in que.

[Tristan Lall]

Design your bumpers so that each segment is removable by one person in less than 10 s, yet won't shift or fall off during a match. This is easy using a locking pin system (if you pay close attention to hole tolerances and alignment), but a bit harder if using threaded fasteners (try wing screws and threaded inserts for woodworking).

For bonus points, consider using the bumpers as robot structure (plywood can be quite strong). In that circumstance, a little extra effort to remove the bumpers (like 60 s per segment) is perhaps justifiable.

[Lil' Lavery]

For mounting the bumpers, 1712 has essentially used the same method for a while. We have 2-3 pieces of aluminum angle per side of the robot, with a slightly oversized 1/4" hole in them. Through these, we secure the bumpers with 1/4"-20 threaded knobs that thread into threaded inserts in the plywood of the bumper. It's not quite as fast as some of the pinned-removal systems, but it's easy and secure.

For the past few years and this year, we've had 100% bumper coverage of the frame, with one segment for each of our four sides. Prior to 2013, the bumpers were red and we had one blue removable "skirt" that we fitted around all four bumpers for when we were on the blue alliance. The skirt was secured with hook & loop straps. In 2013, two adjacent bumpers were red and the other two adjacent bumpers were blue. We then had a reversable "skirt" that could be fitted over either two segments of bumper to complete the color we needed for that match.

[Nuttyman54]

Originally Posted by bachster

Dave, this looks like a very slick way to attach bumpers, but my initial reaction is that it would be in violation of R21-F (must attach to the FRAME PERIMETER of the ROBOT ...) and/or R26 (BUMPERS must be supported by the structure/frame of the ROBOT (see Figure 4-10). To be considered supported, a minimum of ½ in. at each end of the BUMPER must be backed by the FRAME PERIMETER...)

Since your FRAME PERIMETER (definition copied below for reference) is the top/bottom horizontal plate, it seems your BUMPERS are backed by an interior part of the robot, not the FRAME PERIMETER. Alternately, if you intend to define your FRAME PERIMETER as the vertical face which backs the bumpers, then the robot is in violation of the STARTING CONFIGURATION requirement.

Can you (or any experienced inspectors) help me understand how this attachment method is legal?


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.

Yes, the picture Dave attached doesn't really tell the whole story. I didn't understand how it was legal until I saw it with half the bumpers mounted. Look at the attached cross section and it'll make a lot more sense.

[bachster]

Thanks for the clarification, Nuttyman54. It still seems to me like this doesn't meet the intent of "backed by the FRAME PERIMETER..." as my definition of "backed" would be surface to surface (or perhaps surface to edge). In this arrangement, there is still no part of the bumper wood directly touching the outside edge that defines the frame perimeter (or within 1/4"). Yes, there are bolts/rivets just interior to the frame perimeter holding a bracket in shear, but in my mind that's not the same thing. If the C of the frame was less than 5" tall, such that the wood directly contacted the outside edge which forms the frame perimeter, that would be more obvious to me that it meets R26. (Or even if the C was just a little bit shorter, and the brackets went to the outside rather than the inside, assuming the brackets are less than 1/4" thick).

If I were to speculate on the intent of R26, it would be that if the robot was hit hard in the bumper zone, the bumper would be prevented from moving relative to the robot (or at worst, would only move 1/4") by the wood surface compressing to the frame perimeter. In this example, the wood is prevented from moving inward by the shear strength of the bolts/rivets, not by the rigid frame perimeter. It is perhaps further prevented from moving by the length of the brackets which closely match the depth of the "C", but you could easily have shorter brackets or a deeper "C" and lose that feature. If I was inspecting this design, I would challenge that it meets the intent of the rules.

Thanks for sharing this example of a different form of implementation and rules interpretation. As a robot inspector, I'm interested in making sure I understand how the rules are and should be interpreted prior to the events. I would be interested in any LRIs' thoughts on this.

Katie

[Nuttyman54]

Originally Posted by bachster

Thanks for the clarification, Nuttyman54. It still seems to me like this doesn't meet the intent of "backed by the FRAME PERIMETER..." as my definition of "backed" would be surface to surface (or perhaps surface to edge). In this arrangement, there is still no part of the bumper wood directly touching the outside edge that defines the frame perimeter (or within 1/4"). Yes, there are bolts/rivets just interior to the frame perimeter holding a bracket in shear, but in my mind that's not the same thing. If the C of the frame was less than 5" tall, such that the wood directly contacted the outside edge which forms the frame perimeter, that would be more obvious to me that it meets R26. (Or even if the C was just a little bit shorter, and the brackets went to the outside rather than the inside, assuming the brackets are less than 1/4" thick).

If I were to speculate on the intent of R26, it would be that if the robot was hit hard in the bumper zone, the bumper would be prevented from moving relative to the robot (or at worst, would only move 1/4") by the wood surface compressing to the frame perimeter. In this example, the wood is prevented from moving inward by the shear strength of the bolts/rivets, not by the rigid frame perimeter. It is perhaps further prevented from moving by the length of the brackets which closely match the depth of the "C", but you could easily have shorter brackets or a deeper "C" and lose that feature. If I was inspecting this design, I would challenge that it meets the intent of the rules.

Thanks for sharing this example of a different form of implementation and rules interpretation. As a robot inspector, I'm interested in making sure I understand how the rules are and should be interpreted prior to the events. I would be interested in any LRIs' thoughts on this.

Katie

I believe the wood is actually backed the frame perimeter flanges, but that's not captured in my very un-precise powerpoint sketch. Both the frame and angle are made from 1/16" 6061 aluminum.

1983 has run this setup since at least 2011 at regionals and champs and never had an issue with inspections. I believe it also most definitely meets the intent of the rule, which is to provide a robust mounting system for the bumpers to attach to the frame perimeter of the robot and protect our robot, other robots and people from damage. It's one of the most secure bumper attachments I have ever seen.

EDIT: After looking at the robot last night, the top piece of AL angle goes on top of the chassis C, not nested inside, so the angle itself is backed by the frame perimeter. That should clear up any confusion about how it complies the rules.