Arena Assembly, Overpass ... DWG Error?

FIRST General Forum
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I’m not 100% sure where to post this question, and I searched around to see if anybody has noticed this yet … no luck … so it’s going here …

We’re assembling the overpass assembly per the official dwg’s found here

On page 4 of 19, there’s an assembly note for item 13 in the lower center section. It’s for the insert that will tie the overpass sections together. (to couple parts 04 and 05 on pg1)

The note says to turn down one half of the 12" piece … but that doesn’t make sense if both ends of this piece are going to fit inside the section pieces of the overpass.

We are actually not building this piece per the dwg. Instead, we found a smaller diameter piece of pipe that we will use to couple the sections together, without a need to turn it down to the smaller diameter.

Are any of you building an overpass? Have you built this piece yet? Is this a drawing error, or am I missing something. It’s not holding us up … but it’s bugging me … either I’m missing something, or it’s a drawing error.

Thanks.

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I’m not sure where you see the problem.

The tube that makes up the section of the overpass is on Sheet 3, Item 9 has a 1.5" outer diameter, a wall thickness of .083"

1.5" - .083" - .083" = an inner diameter of 1.334" for that Overpass section.

The item 13 that goes into that has a 1.3125 outer diameter on the unfinished side.

1.3125 outer diameter tube (Item 13) goes into a 1.334 inner diameter.

I agree it’s a close fit, but that should be the purpose.

The side you turn down to 1.287 also goes into a tube that has an inner diameter of 1.334" when the Overpass is assembled.

This is meant to have a nice tight fit on one side, and a looser fit on the other.

The Overpass is shipped in sections, and the unfinished side of the Item 13 piece will never come out of the Overpass once bolted in, whereas the finished side (1.287 diameter) will be removed from that next section.

To go a little further in the explanation of this, on page 1 look at the Item 5 & Item 4 closest to us.
Item 4 has the piece firmly fastened in the ends closest to us, and the smaller finished diameter will slide (and then also be bolted) into Item 5.

Remember these fields have to be torn down and reused for several weeks during the competition season, so little things like a smaller diameter and pieces that can just slide together make assembly time (a little more) quick.

This is how I understand it anyways seeing how field have been made and shipped in the past, and tearing down a number of them in the past as well.
Hope that helped.

Were you modeling the field in CAD, or actually building one when you stumbled upon this problem?
Just wondering.
Remember that if modeling this in CAD a “wall thickness” value means you have to subtract that number twice from the outer diameter to get the inner diameter of a tube.

1.5" outer diameter tube with a .083" wall thickness gives us 1.334" inner diameter as shown in my calculation above.

Good luck this year! This is just one of many roadblocks you will face in the coming weeks and months but try not to be discouraged, and always ask for help here or the official FIRST Q&A forums when needed!

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That’s the answer I was looking for … it’s a looser fit on purpose. I get it.

… and to be perfectly honest, we’re not building exactly to print. We have matched the OD’s, but have used smaller thickness tubing for our arena assembly. Saving money and weight and time, but still getting all of the physical dimensions that we need for our testing.

Building it. It didn’t hold us up, as I found some electrical conduit stock that serves that purpose nicely. I was just wondering why the drawing only showed the reduced O.D. on half of the pipe when both ends went into the same size pipes. You cleared that up nicely. Thanks.

You got THAT right … and Thanks Again! No discouragement here. I love this forum … and this family … and this experience. I wish it was around when I was in HS. (Class of 1985!)

Today I got to teach some newbies how to weld! I’m only a 2yr veteran welder myself, but I was able to lay down a couple “stack of dimes” welds to impress! I think we will take and post some pix of the less than perfect welds from some of the first-timer students that tried their hands tonight. :rolleyes: Not everybody can be like Mikey and Paulie on OCC … it’s a lot harder than it looks!

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Nice… If you’re actually building one there is a low cost field option available as well that you knew about right???

http://www.usfirst.org/community/frc/content.aspx?id=7682

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Yea … we almost went that way, but then we figured we’d end up breaking the PVC … so we’re choosing a 3rd option … somewhere in-between.

And we may not build the entire assembly … for now we’re focusing on getting the overpass built … we might just mock-up some of the other assemblies.

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