Cantilever Wheel Bumpers

[JesseK]

Originally Posted by Madison

Unfortunately, the inspectors are not typically qualified to determine what may or may not be a structural member. A plate, no matter how thin, will in some manner affect a frame's rigidity and strength.

Who is the ultimate arbiter of "structure" and of what represents sufficient contribution to the durability of other structures?

I agree.

To stay in compliance with this rule we're using 1/8" thick honeycombed fiberglass plates, and the gaps themselves are relatively small (7" max). We know that this is structurally sound, but to the typical person "that stuff is too thin".

[Kevin Sevcik]

Ultimately, the teams will probably have the final say in whether something counts as structural support for a bumper. But I think everyone should note the GDC's caution that they implemented this because unsupported bumpers were breaking or splintering under impacts. So teams should probably expect to get away with "structure" that doesn't look too incredibly flimsy.. But they should also expect bumpers to be closely examined for damage and for robots with damaged bumpers to be banned from the field until the problem is fixed.

Originally Posted by Tom Line

Calling it structural doesn't make it structural.

1/8 aluminum is pretty thin, and I doubt you'll actually be relying on it for any structural support for the robot - especially not in a single thin strip.

Definitely Q&A this, because as I see it, if you had a judge that understands robot design, they'd take one look at that 1/8 inch thick strip of aluminum and tell you it doesn't meet the rule.

Sure it does.

Anyone see the plastic coverings on the sides of 254 for 06, the last year before bumpers were required? I recall them only using some (fairly) thin polycarb, and they were fine....

[waialua359]

Lets all not forget that the most sound structure on the perimeter is the bumper themselves. Adding an additional thin sheet as the backing is bonus.
I have yet to see a bumper break completely in half due to impact.
If it happened, I bet rarely.
Mandatory bumpers (in how they should be made and mounted) in itself should be self-sufficient. If not, why make them required (considering the purpose is to protect robots)?
If the new rule implies that the bumper themselves may not hold up during a competition, then the rules for how to make them should be modified to meet its objectives in any situation.

[qwertyuiop[]\]

Does the back have to be completely covered? we are planning just to bolt our bumpers on to the second layer of our 8020 frame.
_________________ second layer
|_______|________| first layer

[EricH]

Originally Posted by qwertyuiop[]\

Does the back have to be completely covered? we are planning just to bolt our bumpers on to the second layer of our 8020 frame.
_________________ second layer
|_______|________| first layer

You should be fine. If you really want to be sure, ask Q&A.

<R08> M says length, not height or back. If they had wanted the entire back covered, they would probably have said so.

[Richard Wallace]

From a related thread:

Originally Posted by dlavery

I hate to "break" it to you, ...

I highly recommend reading Dave's full comments on this topic, in the thread linked above.

[Molten]

1/8 inch is not enough. Look at lavery's math. If I was a ref, I'd tell you to go back to the drawing board. Sorry, just my opinion. Not an actual official.

Why is everyone determined on having cantilevered wheels? Can someone give me a bit of info? Is there really much of an advantage?

Originally Posted by Molten

Why is everyone determined on having cantilevered wheels? Can someone give me a bit of info? Is there really much of an advantage?

Weight. That's two less full length chassis members. That boils down to less materials, less fabrication time for the chassis, and so on.

[Molten]

I'm sorry but I'm not seeing it. Anyone got some good pics to describe how this works? Sorry, but its pretty clear I'm not on the west coast.

Originally Posted by Molten

I'm sorry but I'm not seeing it. Anyone got some good pics to describe how this works? Sorry, but its pretty clear I'm not on the west coast.

Search CD media for any of 254/968's drive trains, that's a Cantilevered "West Coast" Drive base.

[JesseK]

Dave's math assumes several underlying principles, and the debate parallels that of traction vs wheel width on carpet. The 'ideal case' can always be argued against in one way or another. Unless you're sending something into space or 7 miles under the sea, the 'worst case' can always be engineered around with protections or tolerances such that the worst case becomes negligible.

In Dave's scenario, extra bumper support would spread the energy of the impact across more surface area, therefore increasing local structure integrity. Those of us who do cantilevered wheels simply need to do the same. What Dave doesn't tell you is that the impact energy has gone through the bumpers it then enters the 'equal and opposite' clause of Newton's laws. Due to the full extent of <R08>, I believe there will be many a pinball robot...now that will be fun to watch....

[GaryVoshol]

Originally Posted by Molten

I'm sorry but I'm not seeing it. Anyone got some good pics to describe how this works? Sorry, but its pretty clear I'm not on the west coast.

http://www.chiefdelphi.com/media/photos/32160 (Not that this really needs more promotion, sorry)

Originally Posted by Madison

Please refrain from making "personal judgements," about rules. If there is a question about how a rule may be interpreted or enforced, bring your concern to the GDC through the proper channels and await their remarks.

Our best guess about what satisfies the criteria of these rules can be detrimental the progress and success of other teams -- especially younger teams that haven't yet learned the ropes.

I thought that was the intent of CD, to thrash out ideas amongst teams and give warnings where we thought them due.

[Madison]

Originally Posted by GaryVoshol

I thought that was the intent of CD, to thrash out ideas amongst teams and give warnings where we thought them due.

We need to be careful about the language we use, however. There are differences between working through problems and writing hypothetically and declarative statements like, "1/8 inch is not enough... If I was a ref, I'd tell you to go back to the drawing board."

I understand that Jason disclaimed his role as an official in his post, but it's a behavior that happens frequently here and I just wanted to call some attention to it so that we all remember that we are not, generally, the arbiters of these decisions and, more importantly, that new teams understand that the things they read here are meaningless when they come to competition.

[JHSmentor]

Originally Posted by Molten

1/8 inch is not enough. Look at lavery's math. If I was a ref, I'd tell you to go back to the drawing board. Sorry, just my opinion. Not an actual official.

Why is everyone determined on having cantilevered wheels? Can someone give me a bit of info? Is there really much of an advantage?

I've seen plenty of people throwing up designs on CD or describing their past robots using 1/8" thick aluminum for their chassis.

Is this truely not the case or are you just referring to the original post saying that it would just be a strip of 1/8" without any angle or channel or gussetting?

Just currious because our robot last year was completely built out of 3/16 sheet - outer wheel plates just held on with standoffs - and, while this was totally bomb proof, it seemed way overkill to me (and heavy to boot).