Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

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

Re: Integrated Bumpers
 

Could you provide a picture?

Re: Integrated Bumpers
 

???

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.

Re: Integrated Bumpers
 

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?

Re: Integrated Bumpers
 

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

Re: Integrated Bumpers
 

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.

Re: Integrated Bumpers
 

Frank,
Yes, several times, as evidenced by splinters on the field. I saw somewhere between 10 and 20 bumper systems sheared off the robot this year. Some of the damage was surprising as threaded fasteners were pulled through the plywood, wood screws were stripped out, and mounting brackets broken. In at least one case there was subsequent robot contact on the unprotected portion of the robot that damaged the frame.
The crash tests were reported to LRIs and have been the topic of discussion with LRIs for several years. We continue to discuss this with new LRI trainees. Anyone can duplicate the test with a section of plywood, some pool noodles and a support that has variable width. What I would call "blunt trauma" would repeatedly cause cracking or complete failure of the plywood when supported at the ten inch interval. "Blunt trauma" would be a robot corner or other geometric protrusion, coming into contact with the bumper assembly. As I remember, Dave's tests were run with a stationary object and with a full robot with variable spacers behind the bumper. The test was run on their practice field.
Andrew, there was no way to run an event without this occurring. Any drive team will tell you that they were standing on rippled carpet by the third day of competition. Most events tried to make adjustments each day. It required peeling the driver's stations away from the carpet and then pushing the stations back into position and then reseating to the carpet. Of course this varied with location as some regionals are way more aggressive than others.

Re: Integrated Bumpers
 

Nope. See page three of this document.

I've seen this happen at every event I've been to. Ever notice the bunched up carpet (that I always manage to trip on) behind the glass?

Re: Integrated Bumpers
 

We had a relatively poorly supported bumper frame that met the letter of the rule (8 inches apart between supports) but only touched the bottom half of the bumper. We did not have cracked plywood failures, but we did have failures in the locations where we glued the plywood together at the corners. We made some quick L shaped gussets to get us through the weekend. No direct plywood splitting failures, though, and we took a lot of hard hits.

Re: Integrated Bumpers
 

We cracked the plywood and bent out frame im about 3 inches during Galileo finals. The frame came within 1/8" of our crio. In the future we will use harder plywood and take advantage of the bumper mounts for added support

Re: Integrated Bumpers
 

I know there are a lot of attachment failures including attachments pulling out of the plywood. I am interested in structural breakage like Spencer's.

Re: Integrated Bumpers
 

I instpected (and was LRI) a lot of events this year. I only saw a few failures of the plywood itself. 2 due to wrong material (0.5" plywood and regular pine board). I did not see the 3/4" plywood failure, but I did see the bent frame behind it. They had bent their frame utilizes a couple pieces of 1/8" think angled.
Most typically, I saw failed mounts, or failed joints due to poorly fabricated items.

With a note on "flip-flop" bumpers. I saw some beautifully constructed flip flop bumpers. They were wonderful to look at and use. I saw many poorly constructed flip-flop bumpers. Typical issue:
1. Not full coverage, IE ends still show significant amount of other color.
2. Flip flop so easy, the robot changes colors mid match!
3. Sagging flaps. When the flaps are down, they frequently have pieces that are clearly below the bumper zone. Refs ask me, and I explain it was in the zone during inspection, refs are clearly agitated, and I have to work with a team to make it better.

FYI: As an LRI or Head Ref: having a saggy bumper non-compliance at an event is a lot like hiking with a peddle in your boot. You don't notice it, and it will bother you at the least convienient times. Until you completely take care of it, it is a nuisance that will show up several times throughout your adventure...

Re: Integrated Bumpers
 

I've seen plywood bumpers splinter. I generally suspect primary cause is buying the cheapest "plywood" available, secondary to unsupported areas behind it.

Wetzel

Re: Integrated Bumpers
 

Here's a picture of the bare frame:
http://team1983.files.wordpress.com/.../wp_001144.jpg


The bumpers mount inset like this (cross section)
http://www.chiefdelphi.com/forums/at...7&d=1391102141

My powerpoint drawing isn't 100% accurate, The height between the frame flanges is about 4", and the bumper wood is 5" tall per rule, so in reality the bumpers extend beyond the top and bottom flanges and are backed directly by the frame as required by rule.

Re: Integrated Bumpers
 

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.
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.

Re: Integrated Bumpers
 

Tristan,
Your link to Dave's comment was a rehash of the actual testing.
To remind everyone why we have these rules. Prior to bumpers (yes there was such a time), robot frame damage that was severe enough to knock a robot out of competition occurred regularly. This fact was enough to make people at the top (Woody and Dean) cringe and look for a better solution. Dave's test and the current bumper rules are a direct result of that. Woody saw that the bumpers reduced damage to robots and that was good enough for him. I worked two double regionals and three single regionals plus the Champs this year. I witnessed bumper damage at every event. Rarely was the result simply a bumper being ripped off or dragging on the field. Rules being what they were, in some cases the robots were disabled.

If you have ever seen a student's face after their robot has been rendered useless, you know why I support the bumper rules. I am not interested in merely satisfying a rule, I want the students to drive in as many matches as they possibly can and good bumpers help them do that. Ike said it pretty well above. If you spent so much time building what you think is the best robot you can build, why would you sacrifice your creation by mounting a substandard or ugly bumper on it? Make it look pretty, make it functional and robust and don't let it fall off.

Re: Integrated Bumpers
 

Having built robots without bumpers, I'll second Al's comment about their value on the playing field. They have also eliminated the "wedge" robot designs that would just go around tipping other robots... there weren't many of them, but I'm glad they are gone from FRC. (Don't get me wrong... I think they are great for Battlebots, but FRC is "non-contact like basketball" as I often describe it.)

I also wanted to add that the requirement for bumpers has probably saved several thousand dollars in damages to school walls, doors, and the shins of slow-moving humans. For most of our robots, they spent far, FAR more time doing demos, test runs, and R&D back at the school and in the community than they did in competition. The bumpers make it easy to let kids take the robot for a spin, and turn the occasional error in autonomous mode testing from an "Oh... that's bad." to an "Ooops."

But on the main topic of the thread... we built our robot almost entirely of baltic birch plywood one year... the bumpers were backed by 1/2" ply. We never did intentional destructive testing with that setup... but I'm pretty sure that it was bulletproof as far as FRC applications are concerned.

Jason

Re: Integrated Bumpers
 

I'm suggesting that teams consider strengthening their robots by building robust bumpers (taking advantage of all that free weight and the inherent strength, stiffness and energy absorption of the plywood), and rely less on heavy frames to meet their robustness targets. I don't think that's at odds with the core objective you articulated.

Re: Integrated Bumpers
 

PINK had a fantastic idea IMO for bumper integration in 2014. They made a welded rectangle out of 1x1 extrusion and permanently mounted their bumpers to it. They had 2 rectangles, one for each set of bumpers. When bolted on, the rectangle became part of their frame. In talking to the team at Chesapeake, it made the bumpers very easy to change and allowed them more leniency with their actual drive frame. I think on the front & back it simply provided a double-barrier for impacts, yet they also didn't need the usual WCD "standoffs" on the side. To me this is a superior design since those standoffs, when welded, have cause my team's wheel base frame to do wonky things when the welder doesn't get it *just* right.

PINK had one rule misinterpretation when they went through inspection, however. They used the rectangle as the FRAME PERIMETER, yet it was weighed and inspected as part of the bumpers. Unfortunately, this caused them to violate the 8" rule for bumpers, even though the inspectors agreed that it was structurally sound. They found a way to appease the rulebook, but the situation does provide insight into how to update the design for next year, assuming the same rules. Technically, the bumpers have to be removable within 10 minutes - thus each rectangle can be a different frame perimeter "configuration", and a student can work for 10 minutes to demonstrate that the bumpers are removable from the rectangle with some effort.

Re: Integrated Bumpers
 

There was a lot of discussion in AL's 2013 robot inspection thread about bumper reinforcement & attachments. I think the upshot of it was a "robust attachment" could be stiffen the bumper as long as it function as the attachment & other bumper rules were not violated (such as weight). So it seems you could use Pink's method as part of the bumper as long as the attachment points on the robot satisfied the frame perimeter rules & the other bumper rules.

Of course in 2014 the GDC got real particular about the bumper definition. Us mortals will just have to wait & see what 2015 brings. :]

Re: Integrated Bumpers
 

If you look at 33's (frankly, brilliant) design, they fix this issue by adding a flange to their outermost "real" frame members which extends over the bumper mounted frame. Thus the frame perimeter is defined by this flange and the bumper frame tucks under it. There are plenty of ways to do this with WCD style frames using "cheater" structural members such as thin plate to extend out and form the frame perimeter. I imagine 233 did something like this.

Re: Integrated Bumpers
 

Zip ties.

Re: Integrated Bumpers
 

This would work, but for 233 it was Thursday afternoon when the issue was brought up by an inspector. There bumpers clearly met the intention of the rules, to be robust and protective, but did not meet the 8" "supported" letter of the rules. In following with the standard FIRST interpretations of "supported" as used on the field, vertical zip ties were used. This satisfied the letter of the specific rule to bring their study, robust, and otherwise legal bumpers into compliance in time for them to compete in all their matches.

Wetzel

Re: Integrated Bumpers
 

Something I've always wondered is why the bumper weight is not just included in the main robot weight? Putting more weight in the bumpers seems disadvantageous to me because it puts the weight much further out. That would make questions about what parts are weighed with bumpers, and what parts are weighed with the robot not matter. I still think size should follow the old rules though.

Re: Integrated Bumpers
 

As I see it, having no contact with the GDC, If the bumpers were weighted with the robot, it would give incentive to skimp on the bumpers & use the weight else where.

Re: Integrated Bumpers
 

Nobody but one or two teams used bumpers at all when bumpers were both optional and counted in size and weight. One of those teams is reported to have rigged their bumpers with weight-transferring devices.

The year that bumper weight was no longer included in robot weight (and the same for size) provided that the bumpers met a standard design, probably 2/3 of the robots out there carried 'em, and they were optional. The next year, 3/4 or more.