pic: How It's Made: 148 & 217 Robots

[Andy L]

Originally Posted by s_forbes

Thank you John and Paul for the excellent info. I've been looking at the 148 models in solidworks (well, the tumbleweed model... I'm afraid if I open the 09 bot my computer will melt) to get a better idea of how you go about designing some of these parts. There are some parts in there that I wouldn't have even thought were bendable. Really awesome stuff!

I started with Tornado... bad choice

[Ricky Q.]

This video and the info that John and Paul provided are just part of the amazingness that comes with being a part of IFI and the FIRST teams they support. This is a company that truly "gets it" and knows that supporting FIRST and programs like it is key to ensuring the success of younger generations.

There are no words to describe how awesome it is to be on the same team as JVN, Paul, Brandon and the other unsung engineers and students that make the Robowranglers what they are. It provides inspiration, motivation and countless hours of entertainment.

-Ricky

[Akash Rastogi]

Thank you very much, John, Paul, and Sean.

[JVN]

Originally Posted by s_forbes

Thank you John and Paul for the excellent info. I've been looking at the 148 models in solidworks (well, the tumbleweed model... I'm afraid if I open the 09 bot my computer will melt) to get a better idea of how you go about designing some of these parts. There are some parts in there that I wouldn't have even thought were bendable. Really awesome stuff!

Pay careful attention to how the parts interact with other parts. Lots of times you can combine individually "wimpy" parts in a way that makes a "not-wimpy" structure.

Try to visualize how the assemblies will respond to applied forces, not just the individual parts.

-John

[mplanchard]

John,

Your movie was just beautiful!

I used sheet metal for laboratory robot design for 5 years. It is light weight and accurate. A few tips on the SolidWorks design side for teams:
-Work with your Sheet metal shop to know their K-factor. SolidWorks uses .5 by default - but this is never the case. Material and shop equipment produce different values. Build these values into the initial design.

-Where do you obtain the material required for the Bend? The answer comes from the Sheet metal Flange position option. The four options are: Material Inside, Material Outside, Bend Outside and Bend from Virtual Sharp.
Material Inside: The outside edge of the Flange coincides with the fixed edge of the sheet metal feature. Material Outside: The inside edge of the Flange coincides with the fixed edge of the sheet metal feature. Bend Outside: The Flange is offset by the bend radius. Bend from Virtual Sharp: The Flange maintains the dimension to the original edge and varies the bend material condition to automatically match with the flange's end condition. Save manufacturing cost and reduce setup time.

- A sheet metal manufacturer maintains a turret of standard relief tools for Rectangular and Obround relief. Obtain the dimensions of these tools to utilize in your design.

- Alternate between 3D formed and 2D flat for every additional sheet metal feature you create. The Flatten feature alternates a sheet metal part between the flat state and formed state.

-Use interference detection in your assembly. You can create configurations of you part to test for tolerance stack up. Make certain you can get tools in to fasten hardware.

-When looking at mating pattern of holes - make certain that you are refernencing dimensions from the same edge. There may need to be a left and right version of a part if the holes are off. Marie

[artdutra04]

Originally Posted by Akash Rastogi

John- would it be possible for you to put on a presentation in Atlanta this year, or even a powerpoint presentation up here on CD, detailing your design process in Sheetmetal in Solidworks? This question is also directed to others who use sheet metal fabrication such as 217, 228, 1771, 1477, 1902 and any others I don't know of.

I've been learning the features in SW but I don't know what works or what doesn't in my designs when, hypothetically, I would try to get them manufactured at a fabrication site. Are there limitations using sheet metal during fabrication?

There are a few general rules that "should" be followed: all flanges should be at least 4x the sheet thickness long; all holes should be at least 2x the material thickness away from the edge of bend; if being made on a turret punch sans laser, the minimum hole size is the material thickness; and the material bend radius is generally equal to the material thickness (there are tables of standard bend radii for each thickness of commonly used sheet metal, but consult with your local shop).

Originally Posted by Akash Rastogi

What are the advantages? (other than speed of fabrication, weight, duplicates)

Other than what you listed, I'd also add their ability to adapt to really interesting geometry.

Since this is turning into a general sheet metal design thread, and since I know I'm not the only one who learns by seeing photos of things, here's a bunch of photos of various features of how 228 has used sheet metal on our last few robots:

The following sheet metal part was the first one that I ever designed (back in my senior year of high school). It allowed us to have a pivoting arm that bolted to an IFI aluminum sprocket, which enabled us to do drive by scoring in autonomous, while retaining the ability to pick up tubes from the floor. This would have been pretty much impossible with anything but sheet metal construction.



Here's a photo of it mounted on the robot: http://team228.org/media/pictures/view/3000


Another interesting feature is the ability to have square holes. While it's not the best thing on earth for stress concentrations (it's actually pretty much the worst), it can allow you to run square tubing right through the middle of parts. On 228, we only use CNC sheet metal parts where we need critical tolerances; otherwise everything else is made with mostly 1"x1"x1/16" box tubing, 1/16" polycarbonate sheet, or various sizes of aluminum angle. So interfacing with box tubing is a great advantage for us that sheet metal offers.

Here's how we used it on our 2009 robot. The 1/16" box tubing ran through the 1"x1" hole and face mounted to the inner chassis rail with bolts. The material around the outside of the box tubing acted as a corner gusset for the rear chassis rail.



Here's a photo with the box tubing super structure attached: http://team228.org/media/pictures/view/4838


Another great feature that we use a lot (as visible in the above photo), is we have .201 (#10 clearance) holes on .75 spacing along many of the important flanges on the robot. While we do model pretty much everything mechanically important on our robots before we fabricate any parts, there are occasions where we want to move something, modify a part, or add new parts onto the robot (last year, it was traction control omni wheel assemblies). Having all these preset mounting holes makes it very easy to do without without needing a drill.


Tolerances aren't an issue as long as you make it clear to the machine shop in your part drawings the critical features and the necessary tolerances. Like Paul (and now John), we use bent sheet metal gearboxes integrated into our chassis (via direct drive, live axle drive trains). Last year I wasn't brave enough to use rivets for critical features, but I'm open to them in the future (if we buy a pneumatic riveter, and as long as the GDC doesn't have inane FRAME PERIMETER rules that make rivet heads illegal). All center-to-center gear distances have .003 added. Here's a photo from our 2009 robot.

[engunneer]

Really excellent thread. Thanks to all above.

I work for a company that makes waterjets, and I'm always happy to show off the parts on our robot, but our robots are bulky and overbuilt compared to these beauties.

I have to say, though, that our 2008 rabbit had a 1 piece frame made of a sheet of 1/4" stainless, and everything just bolted onto it directly. It was one of the simplest robots we'd made, and our first time doing swerve drive. Good thing we weren't worried about weight that year, I think the plate was 28 lbs empty.

designing elegant lightening holes is so much more fun when you have tools like the waterjet or the laser available. A couple of curvy bits really adds to the design, without sacrificing much in strength.

Really impressive design work above. If we had a nice break, I'd love to design stuff like that.

If you can get your hands on it, I'd also recommend the sheet metal tools in Spaceclaim (It's part of the Engineer package). They're lesser known in the 3D cad world, but I've been really impressed with the tools they've made, especially for sheet metal. (for example http://www2.spaceclaim.com/learnmore...Sheetmetal.flv )

[Andy L]

this thread is awesome, really sparking an interest in sheet metal for me