Re: aluminum or steel????
 

aluminum is fun to weld....:) It is a good building material and light-weight. I really don't care because I'm not the one on my team that welds.

Re: which is better aluminum or steel????
 

I definitely agree with that one. Now to mention Matweb, there are some pretty cool aircraft aluminum alloys that would be pretty useful to building a frame and other robot components. By pretty cool, I mean pretty hard, with an ultimate tensile strength of 83,000 psi. Check out the Aluminum 2400s and Al 7475 if you want the high-strength stuff. Most of the 2400s have ultimate tensile strengths in the 60,000's, are moderately weldable, and fairly machineable.

Re: which is better aluminum or steel????
 

In general, in material science, you want to maximize one property while minimizing another; in the case of the chassis of a FIRST robot, the two important properties are weight and stiffness. Because of this, it is often meaningless to compare just the tensile strength, or just the density of two materials. Rather, it is more useful to compare the ratios of these two properties for a given material. In the case aluminum and steel, the ratio of stiffness/density is actually comparable in high strength alloys of both (though by no means insignificant). Because most FIRST robot designs are hardly very well optimized with respect to stiffness/density, other considerations become more important in deciding what material to use. Several important differences between steel and aluminum that make aluminum usually the better choice are

1. it comes in much thinner walled tubing than steel (more efficient shape)
2. easier to machine
3. lower density (makes simple, inefficient designs made from solid stock less costly in weight)

I sort of explained all this in another post and gave some ratios for certain materials (http://www.chiefdelphi.com/forums/sh...647#post307647). I realized now that I used ultimate tensile strength while Young's modulus would be the correct measure for stiffness, but the comparison is still somewhat valid.

Re: which is better aluminum or steel????
 

is it limited to just Al and Steel because i used to play lacrosse and some of the shafts were made from some weird yet very light and strong alloys like a Zinc alloy Shamrock r705
Scandium Brine Sc21
various carbon composites
and countless aluminum alloys

Re: which is better aluminum or steel????
 

Actually Brad- the diamond plate we used is aluminum. Steel is too heavy.

Man- I didn't know we were that much of a target..... ; )

WC

Re: which is better aluminum or steel????
 

For those who say welding steel is harder than aluminum - are you crazy? Maybe I'm doing something wrong? Aluminum conducts the heat far quicker than steel, which makes it tricky to get that TIG weld just right. When I TIG steel material, the puddle stays put and you don't have to constantly play with the pedal as much.

Also, plan your weight carefully so you don't have to deal with lightening holes. I know some teams have resources to mill several hundred holes in their frame, but spending hours and maybe days drilling and milling holes is probably not a good use of time. We made a change last year from a two level frame to a single level frame and instead of just using 1x1 box aluminum everywhere, we switched to using C-channel for the internal struts of the frame and just kept the box material around the perimeter. We also better planned our use of 1/16" thick aluminum for the non-stressed parts of the robot. Also we switched to nylon hubbed sprockets where possible. How nice it was to have our robot done days ahead of the deadline and 9 pounds underweight.