So before I ask the Q&A I wanted to run this by other CDers to see what they thought.
Using the KOP frame the proved axles are 3/8" bolts. This means that either the bolt head or the nut and bolt end rest outside the outermost frame rail.
In order to support the bumper along the entire length do we then have to mount another frame member above the chassis (with no bolt heads or nuts sticking out) running the whole length of the robot and sticking out from the chassis by the thickness of the bolt heads sticking out?
If you do ask, I’d love to know if one is permitted to machine small depressions into the back of the bumper, not exceeding 1/4" depth, exclusively to provide clearance for these fasteners so the bumper fits more snugly against the length of the chassis member/frame.
Official bumpers have aluminum angle top & bottom, so they might rest against the chassis and not wood.
In previous years, we have done that to our bumpers for that exact purpose, and they passed inspection. Of course, we have a whole new set of bumper restrictions this year, so I guess the best answer is to Q&A it…
They would not have passed tech on Galileo last year (several teams had to fix non-compliant bumpers) and should not have passed tech at any regional last year. Mind you, last year did specify NO holes regardless of purpose. This year’s Q&A may be more forgiving.
We asked that exact same question last year and the answer was no. I would think that the tremendous loss of strength due to those tiny pockets would be largely offset by the better support of the bumper by the entire chassis, but the GDC thinks otherwise, or at least did so last year.
Relevant sentence: “Small spaces, up to the thickness of the aluminum clamping angles retaining the fabric covering, will be permitted between the bumper backing and the supporting structure.”
As long as your bolt head is no thicker than the aluminum clamping angle, you’re all set.
This is one reason we decided to go with a wood chassis, with a 3/4" thick piece of plywood on either side of the wheels. The axle bolts can be countersunk, leaving a nice flat 5.5" tall, 26" long mounting surface for the side bumpers.
The kit frame is ok…but it leads to these fun problems…
How about adding a structural piece of 3/8" plywood along each side of the kit frame, with holes to make room for the bolt heads, and countersunk mounting holes on the outside to make room for flat head bolts that attach the wood to the frame.
Eight feet of 3" wide 3/8" thick plywood weighs about 2 pounds, that would be enough to provide a handy mounting surface for the bumpers around two thirds of the BUMPER PERIMETER.
Just an idea…use it, shoot it down, whatever you want
Kevin,
Before an inspector will look at the bumpers, the size (and weight) of the robot is checked. Anything that is part of the robot must meet the sizing rules, including bumper attachment points. Should your design include bolts whose head or shank stick out of the frame, those projections must also fit within the sizing rule. If a team uses an attachment as suggested (i.e. threaded fastener with an internal “t” nut inside the bumper, then the removable fastener passes through the robot frame and is not part of the robot size. See “Cross-section View Figure 8 – 1” in the manual.
Also…
E. BUMPERS (including any fasteners and/or structures that attach them to the ROBOT) must
weigh no more than 18 pounds.
So if we have a frame with say four uprights, the bumper can’t just attach to the uprights? The sides have to be solid? That’s what it looks like the rule says, but the Q&A answer was “Inspectors will be looking for structures sufficient to provide this function.” Thoughts?
Brian
Hey, if you figure out that answer post it here. We tried asking yet another bumper question on Q&A and believe that they are avoiding us.
We are like may who use square extruded aluminum like ITEM for our chassis. We believe that the new rule requires us to reconfigure our design to make sure that the chassis frame makes contact with all 4 “edges” (horizontal and vertical) of the bumpers (plywood backing). :ahh:
So we redesigned the entire chassis versus adding material and adding weight of the chassis.
Please know that the GDC is just as busy and perhaps more so than teams are at this point. They look at the questions (and there are a lot of them) and I would guess they have to make a decision as to which question best asks the question and how to answer it. I would not expect them to sit and wait for a question to be asked and then pounce on it. Please be patient.
There’s another bumper problem with the kit chassis while we’re on the subject. In the short and wide configuration, you end up with a gap in either two or four corners of the frame. (See attached image) This leaves you with a ~1.5" diagonal on the bumper perimeter that cannot be protected by a bumper. Which means it’s impossible to make the short and wide kit frame legal unless you build it 35.5" wide, or know to ignore the instructions, build it 36.5" wide and cut the outside bars long. Or other complicated things that rookies aren’t going to know about.
I’ve posed this to the GDC, and I’m desperately hoping that they rule it legal to wrap the bumpers around this corner or extend them an extra bit to cover it. If they decide that teams will just have to modify the frames to make it possible to legally mount bumpers… Then I’m going to be somewhat annoyed with them and the prospect of helping 50% of the rookies at our regional get their bumpers legal.
And Q&A has clarified that, for the 6"-max robot length requirement, you have to have the backing 6" long, but you can have soft parts extending beyond said length that are part of the bumpers but not counted in the length. http://forums.usfirst.org/showthread.php?t=11316
If you want to follow the letter of the law, by building the kit frame as illustrated in the picture, you have actually created a very short 45-degree angled face to your BUMPER PERIMETER - somewhere in the neighborhood of 1.4 inches. This face has no frame backing to attach the BUMPER to. Never mind that you can’t attach a 6" bumper to a 1.4" space.
Somebody please ask Q&A how to BUMPERize this corner. Following instructions given with kit parts should not lead you to violating the rules.
Yes, it is possible to build the KOP chassis without the corner gap, our frame does not have this gap. However, the directions do specify this gap and I agree with Gary that providing teams with a kit that requires significant modification outside the provided directions in order to be a competition legal frame is not overly helpful to veterans and may even be detrimental to rookies.
The heads of the axle bolts I mentioned in my initial post are also visible in the picture posted by Kevin. These bolt heads are significantly thicker than the angle we would be using to clamp the fabric to the bumpers. My uneducated opinion also says that mounting the bumpers with this frame rail as the “support” and those bolt heads being the only actual contact with the plywood would cause them to be much MORE likely to break not less. A large impact occurring near one of these bolt heads would transfer the force through the small area of the head itself which would likely cause the plywood to crack wouldn’t it?
Squirell, that sounds like it could be the easiest solution. Depending on what the GDC says regarding this question we will definitely look into this possible solution.
