Sheet metal is what the body of your automobile is made of. By golly I think what your talking about is honest-to-goodness 3/16" PLATE. That will do just dandy for any robot is my shop.

Nothing against extruded aluminum, cause i love it to death, except for the fact that it is just too heavy, so i think we are going to eventually go with the aluminum tubing, either round or rectangle. But i do know one thing for sure, we dont have the weight to spare this year..:(

we are using aluminum 2x4 tubing that came in the kit. it works well and is strong but we cant weld a lot of disimilar metals on it.

We're going to use 3/4" square tubing for our bot this year. We're making a steel prototype, but the final version will probably be aluminum.

Re: Too heavy
 

20mm extrusion is something that we've looked into too, and I think that's definitely a possibility to reduce weight, though rough calculations would show the moment of intertia would drop to about HALF that of 1" 80-20 just by reducing the overall width and height (and presumably weight) to roughly 80% (20 mm / 25.4 mm/in) . That's the one reason that we haven't made that switch. Has 20 mm been used by your team in the past?

To keep with the thread:

In the past two years we're always using 80/20, 1010 (1" x 1")... and here's why:

The moment of inertia of 80/20 1010, which is 1" x 1", is .04413 in^4
The moment of interia of 1" x 1" x 1/8 thick box is 0.0570 in^4

The weight of 80/20 1010 is 0.495 lbs / ft
The weight of 1" x 1" x 1/8 aluminum box is 0.511 lbs / ft

So.. for those of you trying to save weight, look again!

Check it out at:
http://www.8020.net/pdf/Fractional/0...%20(31-62).pdf

Obviously though, it's more expensive than box aluminum. We were purchasing it at around $2.50 a foot. Box aluminum is about $1.50 a foot off of www.onlinemetals.com

People tend to make assumptions... crunch some numbers and you'll be surprised what you find!

In addition, the ability to actually CHANGE your frame around makes 80-20 great stuff. You can buy a 100 pack of t-nuts for $.08 each and go to town. Where 80-20 makes all their money is on those brackets and corner squares at $18 each. We make our own and come out just fine.

Matt

Re: Too heavy
 

Though the 8020 extrusion itself may be lighter per foot than box aluminum, don't forget to factor in the weight of the additional fasteners and joining plates required to make it all stay together. If a team has access to aluminum welding equipment, it's probably lighter to weld a frame together from box aluminum than to make it from extrusion -- depending on its design, somewhat.

Re: Too heavy
 

Let's see.

If you're using say 25 feet of 1" 80-20 for your frame, you'll save about .4 lbs over box.

40 1/4-20 bolts at 5/8" long, 8 of those corner fasteners (about .025 lbs each) and prolly about a foot and a half of 1" x .125" angle (at .2742 lbs / ft) gives you fasterner weight total of about .752 lbs...

<math skipped, have faith in my algebra>

So using 1" 80/20 for your frame is about 3.1% heavier than box aluminum, fasteners included. (13.17 lbs vs. 12.78 lbs)

Absolutely worth it IMHO.