Integrated Bumpers

[Orion.DeYoe]

This season one of the Ri3D teams, "Boom Done", did something interesting with their bumpers. They integrated them into their frame. The wooden part of their bumpers acted as a structural element of their drivetrain.
Is there any rule in this past year's rule book that prohibits this? I don't recall one off the top of my head but I could be forgetting.
According to the rules and standard operating procedure at a regional, you have to be able to weigh your robot and bumpers separately. However you only have to do this twice (assuming you play in elims) at each event. And with a bit of care put into the system it shouldn't be too painful to unbolt them for those two occasions.
In the past two seasons (by my estimation) there has been an increasing number of teams switching to reversible bumpers. I'm speaking of the type with a large flap that can be flipped over and velcroed into place to change bumper color. Reversible bumpers are feasible to integrate into your frame as they don't have to be removed every match.
All that being said. Doesn't it seem worth it to rely on 15 lbs of material that doesn't count towards your weight limit for structural support? If you made use of that 15 lbs and used some really good quality wood (something like oak or hickory) you can build a REALLY strong frame with the proper design.
This allows you to really lighten up your frame and possibly devote more structure to extra functions.

[thatprogrammer]

I'm fairly sure 179 has done this in the past, may want to ask one of their members.

[cadandcookies]

I believe 33 has experimented with integrating bumpers as structural elements, but I'm not sure if they've used it in competition. I'm sure they could tell you more. I believe they released a document calling it WASP drive or something of the like. You might try running a search for it.

[Joe G.]

Typically, robots with "structural bumpers" aren't at a complete loss of structure without their bumper -- they are still held together as one piece, and don't use the bumper to bridge frame members together. Instead, the bumper, or more specifically, their fastening system, is used to dramatically reinforce or prevent bending of frame members made with extremely light material, which would never stand up to the forces of FRC on their own, and the presence of the bumper is taken into account when sizing other frame members and connections between them. Bumpers may resist any kind of bending, including upwards bending as in the 179 flat panel chassis, torsional bending, or inwards bends from impact.

See here for a whitepaper on 33's system.

[AdamHeard]

It's legal as long as it's used as the mounting interface (not the literal rule, but the interpretation of the rules).

We tried this (but without making the robot frame itself weaker) for some things we're trying out this offseason. Since we run tubing frames, we can't really make them much lighter if we wanted to and still attach how we want.

Bumpers pictured in background.

[Nuttyman54]

1983 has done what you're describing for the past several years (2011 onward). We permanently mounted our bumpers to the frame with rivets using 1/16th" aluminum angle nested into outward facing flanges on a sheetmetal frame. This lets us use thinner sheetmetal on the frame and still be able to take (and deal) a hit.

The bumper cover is reversible velcro, so we only remove them for inspections and then rivet them in place for the duration of the tournament, effectively making them part of the frame structure.

[DampRobot]

Originally Posted by AdamHeard

It's legal as long as it's used as the mounting interface (not the literal rule, but the interpretation of the rules).

We tried this (but without making the robot frame itself weaker) for some things we're trying out this offseason. Since we run tubing frames, we can't really make them much lighter if we wanted to and still attach how we want.

Bumpers pictured in background.

Woah. I'm loving that frame Adam. I can't wait to drool over it at CC.

[Al Skierkiewicz]

Everyone,
Be careful here..
The rule states that bumpers must be mounted on the FRAME PERIMETER. The FRAME PERIMETER is explicity described in the rules and can have minor protrusions for boltheads, rivets and welds not to exceed 1/4". The bumper must be outside this perimeter (and mounted on it) but can have recesses to facilitate secure and robust mounting of the bumper system to the frame. Any method of using the bumper to hold parts in place must comply with this rule. If the bumper system is backed with metal plates and the plates are used to support other robot structure, than the plates become the frame perimeter and will be inspected as such.
See R2 and R3 and section 4.6 of the robot manual.
The First base kit when correctly assembled will have axle bolt heads that extend out of the FRAME PERIMETER but these are allowed (see above). When incorrectly assembled (bolts reversed), the bolt ends and nylon lock nuts would extend beyond the allowed FRAME PERIMETER protrusions limit of 1/4". The accepted method for determining FRAME PERIMETER is the string method as described in the rules.
Additionally, any parts that are FRAME must be weighed with the robot not with the bumper system. Bumper systems that use metal plate attached to the plywood/wood backing (for mounting purposes or other legal reasons) must meet all bumper rules including weight, and "hard parts" limits.

[Tristan Lall]

I've done the bumpers-as-structure thing before, and heartily recommend it. Use good, strong hardwood plywood (finish grade), and enlist the help of someone with quality woodworking tools (or a milling machine, if you're so inclined), so that it's exactly the size you want. The idea that the frame must provide substantial structural support for the bumpers (rather than the other way around) is nothing but a silly conceit—any support whatsoever satisfies the requirement (R26). But whatever you do, don't make your bumpers difficult to remove as a result—ideally, each segment should be removable by a single person in 10 s without tools.

Presuming the 2015 rules remain similar to 2014, there is very little guidance on what constitutes the part of the mounting system that forms part of the bumper, in contrast to the fairly specific (but slightly geometrically-challenged) frame perimeter rule. You can use that to your advantage, while still complying with the rule.

But you shouldn't let something that is clearly part of the rest of the robot overlap the plywood of your bumpers—that's asking for trouble. Under some years' interpretations of the bumper rules then in force, that's occasionally and inconsistently been ruled legal, but it's a bad idea to attempt it.

[BJC]

Originally Posted by Joe G.

Typically, robots with "structural bumpers" aren't at a complete loss of structure without their bumper -- they are still held together as one piece, and don't use the bumper to bridge frame members together. Instead, the bumper, or more specifically, their fastening system, is used to dramatically reinforce or prevent bending of frame members made with extremely light material, which would never stand up to the forces of FRC on their own, and the presence of the bumper is taken into account when sizing other frame members and connections between them. Bumpers may resist any kind of bending, including upwards bending as in the 179 flat panel chassis, torsional bending, or inwards bends from impact.

See here for a whitepaper on 33's system.

We ran this system in 2013 and it worked very well. The only reason we didn't run this system in 2014 was our drivetrain choice made torsional stiffness unnecessary. For 2015, if we choose to use a drivetrain that requires high torsional stiffness (such as 6wd or 8wd) we will definitely be using the bumpers as a central component of the frame. It's simply too much free weight to waste.

Cheers, Bryan

[zinthorne]

Originally Posted by Nuttyman54

1983 has done what you're describing for the past several years (2011 onward). We permanently mounted our bumpers to the frame with rivets using 1/16th" aluminum angle nested into outward facing flanges on a sheetmetal frame. This lets us use thinner sheetmetal on the frame and still be able to take (and deal) a hit.

The bumper cover is reversible velcro, so we only remove them for inspections and then rivet them in place for the duration of the tournament, effectively making them part of the frame structure.

Could you provide a picture?

[Al Skierkiewicz]

Originally Posted by Tristan Lall

The idea that the frame must provide substantial structural support for the bumpers (rather than the other way around) is nothing but a silly conceit—any support whatsoever satisfies the requirement (R26).

???

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.

[FrankJ]

Admittedly the 2014 game was probably the most aggressive for robot to robot contact since bumpers were required. IE wide open field, no protected areas. The game demonstrated the need for a robust bumper/frame system. Did any body see any plywood failures? Not bumper attachments, but actual cracked plywood.

Yes I missed Dave's tests. Is it published anywhere?

[Andrew Schreiber]

Originally Posted by Al Skierkiewicz

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.

Wouldn't this count as a field fault? What is the tolerance on that dimension of the field?

[techtiger1]

This is why my team insists on building overly rigid frames. I think in 09 we had a small part of the frame bend but it was above the bumper zone anyway.