How strong is sheetmetal?

[lemiant]

I was reading JVN's 2010 build journal (thanks a ton!), and I noticed that there were lots of times that they found the sheet metal wasn't properly reinforced. I understand that it was easily fixed by adding struts, but the problems did occur none the less. In my experience drivetrains, bearing mounts, or most anything made from plain welded 1" or 3/4" tube with 1/8" wall can just be forgotten because it never breaks, even after excessive speed holing.
Is this just because 2010 was much rougher on drivetrains than this year or because of some inherent weakness in sheet metal, or is it something else I have overlooked?

[EricH]

Sheet metal is as strong as regular metal that thick. However, it needs to be have its reinforcements. Flanges, support coming in from the back side, an extra layer, all that good stuff. This is because it's a lot less resistant to bending when hit from the side without those.

The reason you haven't seen the 1/8" tube bend or break is partially because the bumpers have been around to absorb the impacts. I've seen a couple of failures of that material, often around welds or stress points (say, somebody misplaced a speed hole). It also has bending resistance that the sheet doesn't (without the flanges).

And yes, 2010 was rough on drivetrains. The bumps hadn't really been seen that way for years. Plus, 148 was doing a drivetrain type that not a lot of teams had attempted before, even in 8-wheel form (they had 9 wheels).

[Molten]

Reported.

[roystur44]

Alex,

Properly designed and using the right tools for the job. Sheet metal can be stronger, lighter and easier to produce a complex fabricated chassis. Team 971 mainly uses sheet metal and rivets to produce their chassis. The team uses a variety of materials to do the job. We never rule out plastics, extrusion, aluminum tube, wood, pvc, steel, etc.

Here are a couple of shots of our frame before it's put together and gives you a idea how much more you can do with sheet metal.

https://picasaweb.google.com/1045493...82013058320610

[DonRotolo]

Sheet metal is a perfectly valid choice for construction, just as extrusion would be. However to be successful you need to use it properly.

Metal is metal, with some exceptions the same metal will have the same tensile strength in pounds per square inch - whether that's a 1" square or a 1/8" x 8" sheet. Which do you think would be harder to bend in the flat direction? In the wide direction?

Take a sheet of paper. Hold it at one end and swat your computer mouse with the other end. Then roll it into a 1" diameter tube - does the tube swat the mouse further?

Sheet metal uses the advantages of shape (geometry) to allow less material to be used for the same ultimate rigidity. However one must "do the math" for it to work as well as the relative brute force of 1/8" wall extrusion.

[tsaksa]

[quote=roystur44;1067989]Alex,

Properly designed and using the right tools for the job. Sheet metal can be stronger, lighter and easier to produce a complex fabricated chassis. Team 971 mainly uses sheet metal and rivets to produce their chassis. The team uses a variety of materials to do the job. We never rule out plastics, extrusion, aluminum tube, wood, pvc, steel, etc.


Exactly,

I am a new mentor without much experience with using sheet metal in robots. Just my own occasional hobby projects. But I believe many materials such as sheet metal are too easily overlooked.

Remember that almost all automobiles are today constructed with a sheet metal body that has no solid frame or chassis underneath it. Automotive engineers gain the strength and rigidity they need from sheet metal by making careful use of the inherent strengths of this material and applying geometric principles to overcome the weaknesses. Done properly, sheet metal produces a very light, strong, and inexpensive frame.

The biggest difficulty that might face a team wanting to make full use of sheet metal in their design is the expense of tooling. Sheet metal can be easily and inexpensively bent and joined in simple shapes to improve strength and rigidity. However, the complex shapes used in automotive bodies required very expensive metal forming equipment. These complex shapes bring sheet metal construction to very high levels of strength and beauty. But as long as you do not want to push the construction technique to the extreme levels used in auto bodies, you can do a lot with this material quickly, and at a modest cost.

[ratdude747]

Anoher point to consider is how you will be ebnding it if you choose to. accurate bending is half the battle... good sheet metal equipment is a must. if you are using aluminum or plastic, depending on the thickness and alloy/plastic type, you may need to use heat to avoid and minimize fatigue cracks at the bend. this is an often overlooked thing...

what i have heard is it is a lot like crab drive- you either love it and it works wonders or you hate it and its fails... for some it works and some its a waste of time and money.

my advice is to try it in the offseason first and see if it does what you want... if you like it and it still suits your needs once the 2012 season begins, go for it. if not, try something else.