which is better aluminum or steel????

[N7UJJ]

Originally Posted by ZACH P.

Say, do you have any picture of your robot available?

Try these:
http://members.cox.net/n7ujj/marcos842.jpg
http://members.cox.net/n7ujj/MVC-463S.JPG

[Joe Ross]

Originally Posted by [527]phil

i work in a machine shop and steel is alot harder to machine than aluminum,

I think welding is a much more common operation on a frame then other types of machining. It's much easier to weld steel then aluminum.

[greencactus3]

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 "nicer" to the more rookieish teams

[Bill Gold]

I’ve seen a lot of people talking about bolting and welding exclusively, and some saying they preferred bolting to welding since they thought it’d 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 aren’t so obvious. We really didn’t care about the frame’s appearance last year; we just wanted to get it done.

(excuse the mess… there were 5 of us working for days on end, and ~30 straight hours down the wire… none older than 21)

Picture 1
Picture 2
Picture 3

[Andrew]

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 worlds...
aluminum - very good strength to weight ratio
steel rivets - semi-permanent, strong in shear and OK in tension

[SCYTE16]

thnx for the help everybody!!!!

[[527]phil]

I don't believe welding is a good option, it's just more machinery you need to bring to the competition. and I weld aluminum all the time, just cuz it's harder dosen't mean it's not good, no pain no gain. and correct me if i'm wrong but isn't there a no smoke or sparks rule, cuz they had that at our regional last year, and i don't believe that first would approve of welding while people are walking about without protective eyewear.

[Cory]

Originally Posted by [527]phil

I don't believe welding is a good option, it's just more machinery you need to bring to the competition. and I weld aluminum all the time, just cuz it's harder dosen't mean it's not good, no pain no gain. and correct me if i'm wrong but isn't there a no smoke or sparks rule, cuz they had that at our regional last year, and i don't believe that first would approve of welding while people are walking about without protective eyewear.

You can't weld at competitions. Some events will have welders at the machine shop that can make any repairs to welded parts that may fail.

[[527]phil]

O ok, but the regional that my team went to last year didn't have those resources

[i_am_Doug]

Originally Posted by SCYTE16

which is better aluminum or steel for making an outside of a robot????

well i think to go aluminum be caz its lighter then steel but more flimsy

[JVN]

For those wishing to do some actual engineering calculations to compare materials for a given robot application --

I recommend checking out:
http://www.matweb.com/

Lots of cool information there. You can plug in values to your heart's content.

John

[Greg Perkins]

Lets see... *opens "Materials and Processes in Manufacturing" textbook*...

First, ALuminum:

"A number of unique and attracitve properties account for the engineering significance of aluminum. these incluce its workabilty, lightweight, corrosion resistance, good electrical and theramal conductivity, optical reflectivity, and ease of recycling. Aluminum has a specific gravity of 2.7 compared to 7.85 for steel, making aluminum about one third the weight of steel for an equivanlet volume. Sost Comaprisons are often made on the basis of cost per poun, where aluminum is at a distinct disadvantage. There are a number of applications, however, where a more appropriate comparison would be based on a cost per unit volume. A pound of aluminum produces three times as many same sized parts as a pound of steel, so the cost difference becomes markedly less. "

Now, Steel:

"Compared to other engineering materials, the carbon steels offer high strength and high stiffness, coupled wit reasonable toughness. They can be magnetically seperated from mixed materials, and are easily recycled. Unfortunatly, they also rust easily and generally require some form of surface protection, such as paint, galvanizing, or other coating. The plain-carbon steels are genearlly the lower-cost steel material and should be given first consideration for many applications. Their limitations, however, may become restrictive. When improved performance is required, these steels can often be upgraded by the addition of one ore more alloying elements......Steel is an extremely useful engineering material. It offers strength, ridigity, and durability. From a manufacturing perspective, its formability, joinability, and paintability, as well as repairability, are all attractive. As a result, steel accounted for half of the material used in a typical 2000 model Japanese passenger car, and will likely continue at this level. In terms of tonnage, steel is the most recycled material in commerce, nearly twice as much as paper, and far exceeding aluminum, glass, and plastics. Its magnetic properties facilitate easy recovery and seperation from other materials. As a result, about two thirds of the steel production in the United States comes from the recycling of steel scrap."


well there you have it....I knew tackling a course like design and processes of metallurgy and material sciences in college would lead to something.

In my many years in FIRST, I have always had a sweet spot in my heart for aluminum. I think the engineering and properties that it has makes it beautiful. For any of those who cannot come to a decision over steel vs. alum. Look into aqcuiring this book( however be forwarned, it does cost about $150).


Hope everything works out!, Good luck!

[Dick Linn]

Last year we used 1" x 1" x 1/8" wall square tubing to make a ladder frame (single platform). Each corner and cross member was sandwiched between small 1/8" thick top and bottom plates (about 2" x 3") and bolted with 10-32 x 1 1/4" alloy steel cap screws (typically 4 per bracket pair). Internal bracing used short pieces of aluminum angle on the sides to keep the top clear of obstructions. It was strong, very stiff, and required only cutting and drilling. It could also be reconfigured easily. Best of all, it only cost about $40. in materials. The square tubing is a LOT cheaper than 80/20 or other extruded types, about $1./ft., though probably a bit weaker for it's weight. I think it was some softer 5000 series alloy, not 6061-T6. Last year was the first time we didn't have any problem making weight.

If you are on a budget and don't have welding capability, try it. Buy the tubing at a metal supply place in 20 ft. lengths, not Home Depot! Allen head cap screws are about $8./100 at MSC and the nyloc nuts are cheap.

[robolemur1236]

Consider style and temperature as well. Aluminum "cleans up" very well and looks professional and in my opinion, its easier to weld and not as messy as steel. When you deal with temperature you need to consider how much heat your robot puts out and if the metal will become brittle under the temperature, then again it all depends on how thick your piece is

[Kevin Sevcik]

Originally Posted by robolemur1236

Consider style and temperature as well. Aluminum "cleans up" very well and looks professional and in my opinion, its easier to weld and not as messy as steel. When you deal with temperature you need to consider how much heat your robot puts out and if the metal will become brittle under the temperature, then again it all depends on how thick your piece is

Metals actually become brittle under low temperatures. And most FIRST competitions are indoors, so it shouldn't be a concern. Unless, of course, the NJ regional has to be held outdoors this year for some reason.

Heat can affect the temper and ductility of metals, but this is usually pretty darn hot (~500F) So, heat should not be a factor for FIRST robots, really. nothing less than your battery shorting across your frame will generate enough heat to affect the structural integrity of your robot.

And in case any engineer here wants to nit-pick, yes, precipitation hardening aluminum alloys can be over-aged by prolonged exposure to elevated heat. And thus become brittle. But still, most FIRST teams needn't worry about it.