[Tristan Lall]

Originally Posted by Al Skierkiewicz

???

Perhaps you missed the report on tests performed by Dave Lavery and his team that tested various materials, methods of attachment and robot structure backing. The current rules are an outgrowth of that testing. Yes, even 3/4" plywood cracks and fails when struck by a 150lb robot running at the speeds we encounter except when supported by substantial robot structure at least every 8". Even then, repeated hits, the angle of the collision and a variety of other factors (i.e. running into or being forced into the low goal corner) can lead to bumper failure and damage to the robot. Anyone who witnessed this past game, especially in the early weeks of competition, know that even accepted practice in bumper construction failed from time to time. Teams that used a particular style of support (typical in WCD) found that repeated hits to the bumper system caused the standoff style support to punch holes in the plywood or fail altogether. The resulting failure damaged drive axles and wheels.
Due to the repeated impact and the energy imparted this year, fields regularly grew by up to three inches each weekend, as the player stations were driven apart.

I'm saying that as long as your bumper is considered supported (according to the R26 definition), you have satisfied the rule, and have nothing to fear from an inspector, no matter how weak your frame. Furthermore, as long as your bumper is also constructed well, you have little to fear in a collision—but what risk exists is yours to take, and will depend on your design.

Given these constraints, it's silly to believe that a robot's frame must always be the main support member for the robot, when there's also a perfectly good bumper there.

Originally Posted by 2014's 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. Additionally, any gap between the backing material and the frame

1. must not be greater than ¼ in. deep, or
2. not more than 8 in. wide.

If the bumper is legally mounted, it is supported more robustly than the one in Dave's test. Did 116 perform other, more rigourous tests that I don't recall? Also, the bumper support rule (in general form) appears to predate the test.

On the general issue of failure modes, I think we've discussed this before. No matter how they're legally supported, hardwood plywood bumpers will rarely fail catastrophically when struck with other legal bumpers (and many other robot mechanisms), especially if they're constructed using the permitted aluminum clamping angle (e.g. 0.125 in thickness and 1 in leg length). When they do break, the damage is typically delamination and partial cracking. That kind of damage is not even a minor (human) safety risk. The field damage and robot damage risks are not unusually large, and are handled the same way as always: penalize it and/or kill it remotely. Bumper repairs will in most cases be simple, legal and mechanically adequate. Teams obviously expose themselves to some risk by legally building their frame weaker than the bumper itself, but that's no different from any other mechanical optimization that a team may elect.