[FRC Blog] Our Mistake and Q612

[Hallry]

Posted on the FRC Blog, 1/21/16: http://www.firstinspires.org/robotics/frc/blog/Our-Mistake-and-Q612

Our Mistake and Q612

Written by Frank Merrick, 2016 Jan 21

Through Q612 on the FRC Q&A we learned that we made a mistake on the drawing for the Rock Wall. The Rock Wall is actually wider than indicated on the drawing.

When our supplier first attempted to make the Rock Wall to our requirements when we were prototyping, they found that they would not be able to do so because of the proximity of the bends in the steel. They asked if we could adjust the size of the Rock Wall to make them manufacturable without running the risk of distortion. We agreed, but did not make the necessary changes to the drawings that would later be published, as we should have. I’m sorry for this.

In verifying the Rock Walls that we had already been manufactured and delivered, we learned additionally that the height was out of specification. Working with the supplier to understand their capabilities, and considering the time to manufacture, we will be having the current manufacturer remake the Rock Walls to an updated specification that will retain the height as published on the original drawing, but widen the wall to 5.25”, the closest the supplier can come to the original dimension. Attempting to switch to a different manufacturer at this time capable of maintaining the original wall width while meeting our delivery deadlines is not realistic, and would further delay our ability to confirm to teams the dimensions of the Rock Wall they can expect at competition.

I recognize that this will lead to some teams having to rework their designs and defenses. I sincerely apologize for the extra resources the teams in this situation will now need to invest.

The updated drawings have been posted to the Game & Season Materials page (or for direct links: 2016 Team Versions and 2016 Field Components). We have verified all other defenses as being manufactured to the drawings. Further, we will be reviewing and updating our drawing verification process to ensure this issue does not recur.

Again, I apologize for the extra investment teams are now required to make.

Frank

[aldaeron]

Unfortunate for teams, but I am glad to see the rationale behind the decision and that FIRST tried to see if they could eat the change. It is curious that some teams have manufactured the part to the original drawing, yet the supplier cannot.

Looks like another "teaching moment" for the kids about why design reviews are so important in the engineering process (and that life is never fair).

-matto-

[Bkeeneykid]

Originally Posted by aldaeron

Unfortunate for teams, but I am glad to see the rationale behind the decision and that FIRST tried to see if they could eat the change. It is curious that some teams have manufactured the part to the original drawing, yet the supplier cannot.

Looks like another "teaching moment" for the kids about why design reviews are so important in the engineering process (and that life is never fair).

-matto-

My guess is because of they way they manufacture the competition-ready metal parts, they need a certain amount of clearance 45 degrees from each bend to properly bend it. They needed it to be wider because of this, thus this change.

[Cory]

Let this be a lesson to everyone to never make changes to manufacturing drawings without issuing a new rev of the drawing itself...

[Munchskull]

Just making sure I read this right. The hight will still be 4.5" but the width will now be 5.25".

[TGurlik]

Originally Posted by Munchskull

Just making sure I read this right. The hight will still be 4.5" but the width will now be 5.25".

That is correct.

[aldaeron]

Originally Posted by Cory

Let this be a lesson to everyone to never make changes to manufacturing drawings without issuing a new rev of the drawing itself...

Management: "Why is yield of this assembly so low?"

... plane flight ...

Me: "The assembly instruction and the drawing do not match. And they way they actually build it on the line matches neither document. The 1st, 2nd and 3rd shifts make it slightly differently"

[Tom Ore]

I like the new width - it's a nice number...

[Munchskull]

Speculation time. How big of a difference will 3/4" be when it comes to the majority of drivetrains already designed?

[Dan Petrovic]

Originally Posted by Munchskull

Speculation time. How big of a difference will 3/4" be when it comes to the majority of drivetrains already designed?

I actually think this is beneficial to a vast majority of drive systems. If the extra .75" is a deal breaker, then maybe what you're doing is a little too complicated.

[RoboChair]

Originally Posted by Munchskull

Just making sure I read this right. The hight will still be 4.5" but the width will now be 5.25".

Originally Posted by TGurlik

That is correct.

That is incorrect, please refer to Page 148 of the 2016FieldComponents.pdf

The Rock Wall is 4.625" tall overall relative to the platform, it is 4.50" if you are not counting the thickness of the material that makes up the base flanges.

So it will be 4.625" Tall and 5.25" Wide at Competition.

[TGurlik]

Originally Posted by RoboChair

That is incorrect, please refer to Page 148 of the 2016FieldComponents.pdf

The Rock Wall is 4.625" tall overall relative to the platform, it is 4.50" if you are not counting the thickness of the material that makes up the base flanges.

So it will be 4.625" Tall and 5.25" Wide at Competition.

I would like to apologize to Munchskull for the misinformation then. I used the game manual as my reference and in there it is listed as being 4.5 inches high. However, as you said, the field components file shows it as being 4.625 inches tall, including the material on the bottom that is not mentioned in the game manual.

[headlight]

I feel like I'm probably missing something huge here, but isn't 4.5x4.5 steel square tube a standard steel tube size? I've used it all the time for machine frame weldments, the corners are rounded too.

4.5 x 4.5 x 3/16 wall: http://www.metalsdepot.com/products/...ml?page=sqtube

4.5x4.5x.12 wall: http://www.tottentubes.com/square-steel-tubing

I kinda assumed it was a solid steel tube, didn't expect them to make it bent sheet metal. I guess maybe the weight savings from not having the bottom wall?

[ratdude747]

Originally Posted by headlight

I feel like I'm probably missing something huge here, but isn't 4.5x4.5 steel square tube a standard steel tube size? I've used it all the time for machine frame weldments, the corners are rounded too.

4.5 x 4.5 x 3/16 wall: http://www.metalsdepot.com/products/...ml?page=sqtube

4.5x4.5x.12 wall: http://www.tottentubes.com/square-steel-tubing

I kinda assumed it was a solid steel tube, didn't expect them to make it bent sheet metal. I guess maybe the weight savings from not having the bottom wall?

It's probably made out of bent sheet for mounting purposes as well. Otherwise they'd have to weld the square to a plate, which would be heavy and possibly significantly more expensive. Two plates on the edges would probably have distortion issues with the welds. Bent sheet is (relativlely) cheaper and/or looks better (cheap means stick/MIG welds which have splatter and/or slag issues, TIG is pretty but relatively expensive).

[headlight]

Originally Posted by ratdude747

It's probably made out of bent sheet for mounting purposes as well. Otherwise they'd have to weld the square to a plate, which would be heavy and possibly significantly more expensive. Two plates on the edges would probably have distortion issues with the welds. Bent sheet is (relativlely) cheaper and/or looks better (cheap means stick/MIG welds which have splatter and/or slag issues, TIG is pretty but relatively expensive).

How are they planning to mount this? The prints don't show any bolt holes, so it seems like they're going to have weld this thing regardless (they are already welding the moat and the rough terrain).

The bent part is already made out of sheet steel. I guess you could TIG weld it if you want, but most welders I've met can do pretty clean welds with a MIG and steel is generally easier to weld than aluminum. The distortion issues are valid, but I think they could be avoided by a competent welder.