Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

1/4 inch Styrofoam bumper spacers may be pretty popular
this year, considering the vagaries of the rules and fact that
robots are almost always weight challenged. We will see
what happens.

Eugene

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Kika and others,
The bumper design is intended to protect your robot. The GDC looked very hard at the effects on last year's damage and saw that bumpers, as designed, indeed protected our robots. Part of that design is the backup frame structure that prevents the bumpers from damage due to extreme flexing. Robot inspectors will evaluate each bumper implementation to determine if, in their opinion, the bumpers satisfy the rule. If anyone thinks that a 3/4" slab of plywood can absorb the hit of two 150 lb objects by itself should look for a post from Dave Lavery last year on this subject. The bumper system includes the backing frame structure and will be evaluated with that in mind. To that end, the GDC has allowed you to "pocket" the bumper (not drill holes through the material that will weaken the plywood) to allow the bumper to use the backing of the frame to strengthen the system. If you have two bolt heads at each end of the bumper that cause it to be separated from the frame for 35", some failure will occur. If your inspector asks you to make four small pockets, I don't think he/she would be out of line. Please be prepared to remount your bumpers during the inspection process following weigh and size. This step will be needed to evaluate the bumpers, check for height and ball intrusion and kicker extension if any.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

If the GDC has looked very hard at the bumper design, then how is it they overlooked the most critical element - the plywood? There's a whole lot of difference between the 13 ply Baltic Birch plywood we use and the 5 ply soft-wood junk they sell at Home Depot. The ruling spends just one word, "plywood", on the most important part, but goes into great detail and updates about trivial air gaps. It just doesn't make sense!

Al - I'll bet you a dollar to a doughnut (no Krispy Kreme please) that a 35" slab of our plywood will take that hit. ;)

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

In 2007 we had a bumper of high quality plywood unsupported over about 30 inches. It snapped like a twig our first match. We replaced the wood and it happened again so we played the rest of the regional with a broken bumper. At our next regional we replaced it with cheep Lowe's plywood and it lasted almost the entire regional before it broke (it had more spring.)

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Ah - there's our mistake, we should go to Lowes instead of Home Depot. :)

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

No comment...
Agreed on plywood type. Most teams are going to opt for the cheapest available or what ever is left over from another construction project. Sam's experience is what the GDC is trying to avoid and what we are trying to inspect.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

I'll take your bet ;)

In 07 we snapped our front bumper 3 times, including once with 4 pieces if 1/2" angle aluminium. It took less than 30 seconds to snap it and we couldn't move faster than 6'/sec.

* Bumper was unsupported across 35" of frame giving a 1" space behind it.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Not that I don't like Home Depot I just cant stand all that orange.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

I would rather deal with sickening orange than the terms "FRAME PERIMETER" and "BUMPER ZONE"...

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Maybe I should have stressed more that issues in life like this are never white-and-black, but usually blurry grey areas that need context on a case-by-case analysis.

Doing any kind of classified work with need to know basis obviously means you don't ask questions and just do your job. But for non defense/classified work, I've seen first hand or heard of many other stories where the given specs were indeed misguided, and upon further back-and-forth questioning, a mutually beneficial agreement was found.

One such case a professor of mine told me recently, was of a large manufacturing corporation contracting out work for a french fry sorting machine. But when one did the math, their requested weight tolerance for the bag of french fries was 1/4 the weight of a single french fry. How would you bag something as multifarious as french fries and keep a weight tolerance of 1/4 of a french fry? Had my professor's company simply accepted these specs without asking questions, they would have had to create an unnecessarily complex sorting machine to sort individual french fries by weight and bag them one at a time, possibly with a french fry slicer to cut fries in half to get within the given weight specs. This would have been a much slower and more expensive machine than would have been necessary, and would have cost the client more money (both initially and in annual O&M costs) and possibly would have cast the contracted company in a bad light for coming up with an unnecessarily complex and expensive solution. But...

When they asked their client and showed them the math that the given specs were +/- 1/4 of a french fry, the client acknowledged the error and redid the specs to allow a wider error range.

For myself personally, I've worked for a company which produced an integrated system for clients that lacked X feature which all competitors had, but only because our integrated system was better designed to eliminate the need for X feature without any side effects other than a cheaper bottom line. Because most competitors had X feature, bids would often come in requesting this given feature, despite the fact that X feature was notorious for never actually working in the environment they were subject to. Nearly all of the time, when we talked to the clients and explained that our system was designed in a way to eliminate the need for X feature, saving initial and O&M costs, and that most competitors' X feature would almost always fail within three months of installation (and would then be bypassed anyway by the client's technicians), the clients would come to a mutual understanding and accept our bid.

Thus, it's all about context. Sometimes it's appropriate to question the given specs to better serve the customer (potentially saving them money), other times just do your job and don't ask questions.

Both can be done without negatively affecting each other. And I understand your reasoning on this; plenty of times in the past I've posted that teams shouldn't whine when other teams have "better" robots or "better" facilities, but they should instead work harder to become one of those said teams. But for those cases, that's an example where the cause for the individuals' whining can be directly attributable to their own specific actions (e.g. if they work harder, they can fix the situation they are in). In this case, no matter how hard one works, the bumper rules are still the bumper rules, and thus it's acceptable to "whine" to make sure those who could rectify the situation have a true understanding of the impact of said rule on the community at large.

I've personally always been one who calls things like they see it. Maybe it's blunt, but it's better to get right to the point than dance around the tree sugarcoating problems and hiding how they truly impact the affected people or entities. Bolt heads behind bumpers are completely understandable, and so is the allocation for small pockets in the plywood backing to allow bumpers to sit flush for strength reasons.

But when the rules as written would not even allow for a 1/16" high button-style rivet head above or below the bumpers... that's just a needlessly restriction on FIRST teams. 50-75% of robots should not show up at their first event unknowingly illegal; if it does occur, then that's obviously a sign the rules were too bloated and/or full of ambiguities to be comprehended by the average Joe FIRSTer.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Robots shall have a base-plate of prefabulated plywood, surmounted by a malleable logarithmic casing in such a way that no two spurving bearings can be in a direct line of contact with another robot's pentametric fan. ...:D

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

At risk of going even farther off on a tangent, I thought I’d clarify this sentence. Working in this type of environment does not prohibit communication instead it limits how and with whom that communication occurs. If anything, communication within these projects can be even more crucial because we are frequently pushing the envelope of technological feasibility. My experience across a spectrum of projects with security restrictions is that engineers maintain an almost constant dialog with program management, peer engineers, customer engineers, R&D labs, subcontractors, etc. Within really complex systems, it is nearly impossible for any one person to be an expert in all detailed aspects. Thankfully, we work in integrated teams so that we don’t have to. There are definite down sides of working in restricted environments such as this but you can also do some really cool engineering.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

The requirement for 100% full, CONTINUOUS, intimate contact of bumper plywood with the entire perimeter of the frame is rather excessive. Especially when there is no similarly draconian requirement for exactly where within the 5" height of the plywood that the frame makes contact. If frame only touches at the top or bottom 1" of the plywood, the bending torque force with a 4" cantilever of unsupported plywood at middle of side is also very serious with dynamic impacts!
It would make much more sense to have a simple spec for a maximum allowed spacing distance between points of support of frame in contact with bumper's plywood. If this spacing distance was between 3-6" the chance of breaking plywood would be minimal.

We currently have three aluminum plates on all four of our bumpers, one at each end and a 3rd in the middle. They are mounted with flat head screws going both ways, outward into T-nuts on plywood and inward into T-nuts inside frame slots. Screw heads are all countersunk into the thickness of the aluminum plate. The plates also stick up higher than the top of the bumper so that we can access the mounting holes for the plate-to-frame screws.

We were assuming that these plates were part of the bumper, since they fit within the 1" max. thickness of plywood plus mount H/W, but now we have the issue of plates only giving intermittent contact with frame-to-plywood. We also have the issue of plates sticking up past plywood. Is this still legal, as long as the aluminum plates still remain within the 10"-16" above floor bumper zone?
Perhaps we should consider treating the plates as part of the frame, and then filling in the gaps between the plates with similar thickness aluminum bar along the frame face, to give a 5mm expanded frame perimeter. Fortunately, we are not at the max 28"x38" size already and have some room to do this.
-Dick Ledford

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Somehow, I prefer the days of battle scars to the bumpers of today.

Re: legality of bolt and screw heads breaking plane of chassis meeting bumpers
 

Dick,
I am your Lead Robot Inspector in Chicago. I will lead you through the fine points in two weeks. We will get you playing, guaranteed.
BTW, I assisted the original Francis Parker team, Frank's Garage and came to the school then to check on progress.
See you in a few weeks or you can come up to Milwaukee next week and see how things go at a regional event. If nothing else, come up on Saturday and check out other teams and watch the game play. I will be inspecting there as well. Just ask for Big Al and someone will point me out.