which is better aluminum or steel for making an outside of a robot??? 
Not sure what you mean by āangled outsideā? We have used aluminum for our frames since we started building robots. Yes It bends every now and then, infact we bent team 25ās steel diamond plate in 2003.
The bends we get are nothing a hammer and fire canāt fix. :ahh:
Here is a picture of 2004 frame:
http://www.tigertrons.com/Pictures/2004/Build%20Season/100_0535.JPG
Edit:
We use 1/8āā wall thickness by 1.25āā angle aluminum.
I suggest that you come up with a list of attributes that you think are important for the frame of a robot. Then you can compare each one on an attribute by attribute basis.
Strength and cost are two possible attributes, but there are many more that you can compare.
There isnāt a correct answer for your question. Thatās why you need to break it down into smaller steps.
Not only is is just a factor of strength and cost, but also weight. You need to figure out if any parts of your robot will undergo tension, compression, or excess stress. Then, begin assigning materials to sections. To other way is to use what you have where you can use it 
Our team mostly uses aluminum on our robots, but for things that fall under great stress, like hooks, latches, and wheels, we use steel.
Aluminum is durable, lightweight material that can be easily cut, drilled into, and be bended into certain angles and shapes; not to mention it is inexpensive and abundant. But aluminum can also break under high stress and can also wear down more easily than steel.
Steel in incredibly strong, and can not bend as easily as aluminum. But, however, steel can not be cut or drilled as easily as aluminum. Steel is also heavy, and can be good for balancing your robot, but donāt use too much! Steel is also expensive, making a 4X4 sheet cost about $40! The major factor, however, is that steel can rust, and can eventually break down after a long while; so if you are planning to use a robot for a long time, I suggest using as much aluminum as possible.
there is only one thing i can sayā¦
Aluminum is way cheaperā¦ Steel is way stronger and heavier. Most of the teams in FIRST uses Aluminum on their robot. this past year my team has used Steel gears for the transmission. but my suggestion would be use harden aluminum for gears and aluminum to build your robot. Aluminum gives you the option to play with weights. good luck.
Nope. Steel angle is about half the price of aluminum angle.
Joeās rightā¦ i was debating about itā¦ i should have researched before i postedā¦ sorryā¦ :]
There was some really good discussion in this thread.
Enjoy! =-]
steel is cheaper, stronger, and comes in a variatiy of shapes sizes hardnesses and flavors
Itās also denser than aluminum. Aluminum also comes in "a variety of shapes, sizes, and hardnesses,ā so that shouldnāt be any reason to choose steel over aluminum as your material of choice.
If youāre not into using something like 80/20 (or other comparable āerector setā materials) I would suggest a basic frame be made out of something like 1ā x 1ā x 0.125ā thick or 1ā x 2ā x 0.125ā thick aluminum tubing. Portions of the frame that you would assume wouldnāt be exposed to much stress can probably be made out of .0625ā thick aluminum tubing. You can decrease the weight of your frame and other components by drilling lightening holes in the tubing, as well.
A good example would be the robot I worked on last year.
The lower and upper arms were 3" x 3" x 0.125" aluminum tubing and the gripper portions were 1" x1" x 0.125" aluminum tubing. We saved a lot of weight with those holes.
I would second Georgeās suggestion that you read the thread he has linked in his post above, if you havenāt already. Itās always good to see your posts, George. It feels like such a long time since the Tigerbolt days. I hope everythingās going well for you, man.
-Bill
Aluminum is also easier to work with, i know not many machines in our shop can handle steel. Plus as mentioned before it is much lighter. We have used aluminum on all three of our robots and we have had no problems.
Answer: None of the above
Team 842 has used the fiberglass from Creative Pultrusions for several years. http://www.pultrude.com/
Itās the material of choice for us. Several reasons:
5 times stronger than steel for its weight.
Lightweight
It can be worked with hand tools - drill, hacksaw, screwdriver. Field repairs could be made with a Swiss Army knife that has that little saw!
If anything breaks, we can fix it in the pit wihout welding, machine shop, etc.
Electromagneticly transparent (No radio wave problems)
Wonāt corrode
You can buy it in all kinds of forms: I beams, angle beams, round tubes, sqare tubes, etc.
Its fantastic stuff.
And ā¦ no they donāt sponsor us ā we tried, though. They should!
yeah aluminum is definatly my metal of choice, i work in a machine shop and steel is alot harder to machine than aluminum, itās also usually heavier. hmmm that fiberglass sounds like it might be a good material, iāll have to check it out for my team.
Say, do you have any picture of your robot available?
I think welding is a much more common operation on a frame then other types of machining. Itās much easier to weld steel then aluminum.
im sure plenty of teams weld, but teams like us with limited resources and plenty of mistakes we find along the way, nuts and bolts are the best. so aluminum is probably ānicerā to the more rookieish teams
Iāve seen a lot of people talking about bolting and welding exclusively, and some saying they preferred bolting to welding since they thought itād be much harder to repair a broken weld. May I suggest bolting, then having your frame welded with the connecting pieces on, and then taking the connecting pieces off (while keeping them around). This provides you the weight savings, while also allowing you to be able to make-shift bolt and problem you might run into. This is what we did on the robot I worked on last year. In fact, you can see some of the bolt holes near the joints of the frame. It may not be the prettiest thing in the world up close, but that can be worked around or designed in such a way that the bolt holes arenāt so obvious. We really didnāt care about the frameās appearance last year; we just wanted to get it done.
(excuse the messā¦ there were 5 of us working for days on end, and ~30 straight hours down the wireā¦ none older than 21)
How come no one talks about riveting? Yet another alternative to welding (permanent) and bolting (removable but heavy).
Aluminum for the framing materials and steel rivets for the joins gives the best of all possible worldsā¦
aluminum - very good strength to weight ratio
steel rivets - semi-permanent, strong in shear and OK in tension