Re: Contradicting dimensions?
 

And why can't they just give us the field model they made all the drawings from...

Re: Contradicting dimensions?
 

Possibly one of the most massively misinformed posts I have seen so far this year.

Either that, or someone has been stealing a bunch of checks from several GDC members....






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Re: Contradicting dimensions?
 

Are you saying, there is not ONE paid engineer on the FIRST staff?

Re: Contradicting dimensions?
 

LOL. How many members on GDC? Less than 20 I guess? Generate hundreds of pages of documentation, which is then proof read & scrutinized by thousands of mentors and dozens of thousands of students, all looking for loopholes......

I'd like to say great Job GDC, IMHO more loopholes were closed this year prior to kickoff than in prior years.

Re: Contradicting dimensions?
 

Oh, I am quite sure that there are several paid engineers on the FIRST staff. But that is irrelevant to your original comment.
I am sure the entire GDC would thank you for the comments. There are actually only 8 formal members, not 20.



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Re: Contradicting dimensions?
 

Technically less than 20. :rolleyes:

I agree that the drawings DO make you have to stop and think, but I have never found them to not ultimately provide all the information necessary.

Re: Contradicting dimensions?
 

Like I said, this kind of thing is normal not only in any industry, but FIRST.

It's easy to end up with conflicting dimensions and tolerances on the same drawing, let alone across separate documents prepared by a staff. The manual likely isn't written at the same time or by the same people who prepare the field drawings. A minor miscommunication, last minute change or just a straight up typo is all it takes. Catching these errors requires careful proofing and, as has been pointed out, FIRST has neither the time nor the staff to catch all errors. All you have to do to deal with these situation is designate the preferred document and refer to that, in this case the field drawing. In general, drawings are going to be updated and proofed more often then a manual or other document.

For instance, most production drawings have an production manual or guide that goes along with it. This contains general information about the part or assembly like preferred processes for certain features, general tolerances, material selection etc. But when it comes time to build the part, the dimensions, tolerances, surface finishes etc. are always pulled from the drawing.

If in doubt, refer to the revision number and date. The manual may or may not have this, but the drawings will. Use the latest revision you can find. FIRST's website will always be up to date. Most drawings will also have a revision block, detailing changes.

We've been dealing with unclear or incorrect field documentation since the 90's. Part of the challenge is that field elements can and do change in detail as the build progresses, and sometimes even during regionals.

Re: Contradicting dimensions?
 

I really fail to see how its even possible to end up with conflicting dimensions on a single drawing, if it was made with any remotely recent CAD program. And really, for the field, I don't understand why there should be conflicting dimensions across different drawings. I'm sure that they draw it up in Inventor or AutoCAD or similar, and then make drawings off of the model. If you use the same model for the source of your drawings, then the dimensions have to add up.

Re: Contradicting dimensions?
 

I've modeled the center section of the field (basically the only part your robot should be interacting with anyways.)

http://www.3dcontentcentral.com/Down...=171&id=183867

You can download it in varying file formats from here.

Re: Contradicting dimensions?
 

I'm laughing again at the lack of thought as I try to print out the 38" diameter target on our pretty much industry standard 36" wide plotter...

Re: Contradicting dimensions?
 

Would a metric plotter be 39.37" wide? :rolleyes:

Re: Contradicting dimensions?
 

Hmmm. That is strange. Because I am noting that our industry-standard 44-inch wide plotter has absolutely no problem printing out the target. On many different sizes of industry-standard paper. Including the industry-standard ISO B-series Size 0 sheets and the industry-standard 44-inch wide rolls.

Before branding something with the "lack of thought" label, one might consider that "your" standards may not be "the" standards. Neither is right, neither is wrong. They are just different.

-dave




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Re: Contradicting dimensions?
 

I'd rather go by this picture taken at the NH kickoff that shows a field within tolerances. Last year we designed for tight field tolerances and got bitten by it in Atlanta when the fields sunk some due to weight on the layers of softer materials* which caused us to regularly get stuck in one spot. Never again will we design for tight field tolerances, ever. 17.5" or less, ftw.

*('regolith' on top of carpet on top of rubber on top of hard floor)

Re: Contradicting dimensions?
 

OK...lol...you got me...

Re: Contradicting dimensions?
 

In this case, FIRSTs drawings are right. It was the manual that got it wrong. That sort of cross documentation error is common no matter what you do, and I think it's pretty easy to imagine how that happens. Production drawings often enough aren't made with the benefit of having the entire design modeled in the same program. A lot of drawing sets are a collage of the output of several different programs and individual models. So it is possible to end up with two different dimensions for the same feature, and it happens surprisingly frequently at least before they get proofed (my job for a short while). This is slowly changing as individual programs get better at 'doing it all', but for the foreseeable future things get made with a mix of programs, each good at some aspect of the model.

The biggest problem is just plain ol' over dimensioning. It's a frequent cause of mixing up tolerance levels and ending up with a design that calls for two different levels of tolerance for the same feature. When that happens the dimensions are conflicting. Even though they 'add up' they mean very different things when it comes time to making the part.