which is better aluminum or steel????
 

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

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

Not sure what you mean by "angled outside"? We have used aluminum for our frames since we started building robots. Yes It bends every now and then, infact we bent team 25's steel diamond plate in 2003.
The bends we get are nothing a hammer and fire can't fix. :ahh:

Here is a picture of 2004 frame:

http://www.tigertrons.com/Pictures/2...n/100_0535.JPG

Edit:
We use 1/8'' wall thickness by 1.25'' angle aluminum.

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

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 isn't a correct answer for your question. That's why you need to break it down into smaller steps.

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

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 :)

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

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 don't 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.

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

there is only one thing i can say...

Aluminum is way cheaper... 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. :)

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

Nope. Steel angle is about half the price of aluminum angle.

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

Joe's right... i was debating about it... i should have researched before i posted... sorry... :]

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

There was some really good discussion in this thread.

Enjoy! =-]

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

steel is cheaper, stronger, and comes in a variatiy of shapes sizes hardnesses and flavors :)

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

It's also denser than aluminum. Aluminum also comes in "a variety of shapes, sizes, and hardnesses,” so that shouldn’t be any reason to choose steel over aluminum as your material of choice.

If you’re not into using something like 80/20 (or other comparable “erector set” materials) I would suggest a basic frame be made out of something like 1” x 1” x 0.125” thick or 1” x 2” x 0.125” thick aluminum tubing. Portions of the frame that you would assume wouldn’t be exposed to much stress can probably be made out of .0625” 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.

Picture 1
Picture 2
Picture 3

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 George's suggestion that you read the thread he has linked in his post above, if you haven't already. It’s always good to see your posts, George. It feels like such a long time since the Tigerbolt days. I hope everything’s going well for you, man.

:)

-Bill

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

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.

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

Answer: None of the above

Team 842 has used the fiberglass from Creative Pultrusions for several years. http://www.pultrude.com/
It's 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)

Won't corrode

You can buy it in all kinds of forms: I beams, angle beams, round tubes, sqare tubes, etc.

Its fantastic stuff.

And .. no they don't sponsor us -- we tried, though. They should!

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

yeah aluminum is definatly my metal of choice, i work in a machine shop and steel is alot harder to machine than aluminum, it's also usually heavier. hmmm that fiberglass sounds like it might be a good material, i'll have to check it out for my team.

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

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

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

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

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

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.

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

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

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

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

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

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

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

thnx for the help everybody!!!!

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

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.

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

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.

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

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

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

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

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

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

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

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. :rolleyes:

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!

aluminum or steel????
 

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.

Re: aluminum or steel????
 

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

Re: aluminum or steel????
 

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.

Re: aluminum or steel????
 

Isn't aluminum significantly harder to weld then steel? Steel can be welded with a torch while aluminum requires TIG/MIG because of its corrosiveness.

Re: aluminum or steel????
 

This statement is just wrong. Aluminum is not easier to weld than steel, and I think anyone who has ever welded in their life would agree with me. Maybe if you're welding stainless or something

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

aluminum is sturdy and lite but is easly warped or damaged

steel isn't light but is stronger

so it's kinda up to your prefrences and ideas :D

Re: aluminum or steel????
 

dude yeah aluminum is sooo hard to wield and just get right.

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

Actually it depends on the alloys being used. Some top grade aluminum alloys, such as 7075, are close in strength to low carbon steels such as 1018. However the steels will be stiffer, that is they will deflect less under a given load, than any aluminum. So you can use a stiff heavy material or a lighter not so stiff material for the same job. How much deflection you can tolerate is the descrimating factor. Many times determining the proper material for a job is pretty difficult. That's why we have Materials Engineers!

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

We riveted this year, and we loved it.

Go to home depot, and for $15 you can get a rivet gun, and for about $5 dollars you can rivet an entire frame. You just have to think a little bit before you rivet. Do it with reckless abandon, and you'll suffer. Do it well, and I think you'll come to love it.

And for that extra bit of permanence - braze. Brazing aluminum is within the financial means and skills of almost every team as long as you follow safe work practices. For the low budget team, Burnz-o-matic makes a cheap kit that works (but the O2 gets pricey if you do too much.) I would encourage you to look up info on welding, brazing, and soldering - find out the difference.

Rivets and Braze - what a good mix IMHO. Low cost and does the job.

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

This year we used very few bolts on our frame, only the side plates were bolted on to allow access to our tracks. We don't have welding capabilites, and our frame is made out of boxtube. Very hard to bolt 2 x 4 tubing without using really long bolts, and risking crushing it. Instead we used 1/4" STEEL pop rivets. They are great, almost as strong as a bolt and easier to put in, and you can do it anywhere easily. The only catch is you need a really big rivet gun. Ours was about 2 feet long and looked more like bolt cutters than a rivet gun.

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

Oh oh... here's how to get around that. We used the 3/16" rivets. Almost 1/4" :) And you can use a tiny, cheap rivet gun (about the size of an average hammer.)

We did 1/4" rivets last year - that was hard. The rivet gun was actually called the "Big Daddy Rivet Gun". And you can get (2) 3/16" into a 1" X 1" spot.

Sorry - I love rivets!
Arrow's website, the rivets we use

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

We used tons of rivets on the arm. It was all made from flat .040 sheet metal (aluminum) that was lasercut then bent picture In some (higher stress) areas the rivets worked a little loose over time. While it did come out very nice, I still think extruded aluminum box tubing is the way to go for any frames or arms or anything. With the sheet metal we were able to make a very thin wall box for light weight but with extruded box tubing you could just surface (machine) down the sides to make it thin too and it would be stronger because it is one piece.

As for the issue of cracking welds, if you have a good welds then you will not have a problem. If the welds are not coming out nice, then of course they are likely to crack.

You can see a picture of our frame and the nice welds (lower structure, upper structure was a rush job) here picture For the frame itself, it is only 11 lbs. It is all 1/8" wall tubing. Thinking back, we probably could have gotten it down to about another 1/2 lb by going a little narrower on the tubing on the side rails.

The only steel in our robot besides gears, sprockets, and chain is in shafts. All the shafts are steel but some of the larger ones are bored out through the center for weight savings.

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

Check out different alloys of aluminium. It makes a difference, but costs more. I think the kit frame was an alloy of sort, although I'm not sure what it was specifically. Anyone know?

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

something in the 7000 series, I think.

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

I would go with Aluminum - Its easier to play with ( Weight Wise ) Steel is just too hard to lighten up, If you build the frame the right way and Identify and take care of the weaker parts of the frame then everything will be alright. Depending on what stock you use as well will help a robots strength

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

Actually, I view the situation as quite on the contrary. It is much more effective to take more wieght out of steel parts because they have more mass per unit volume. Say you want to take a pound out of 1/4" aluminum plate. You'd have to drill 50 1" holes! :ahh: But if that was steel you'd take out a lot more than one pound with that many holes.

But all the weight you can take out of steel did come from somewhere. It comes from the fact that a steel part is heavier to begin with. So, you can start light with aluminum and if you are still over than there's not a whole lot you can do. Or you can start heavy with steel and if you are over (which you probably will be) you can probably remove a lot. So, it is a tradeoff.

Now, for "ease" of lightening, I suppose you are correct afterall in saying steel is harder to "lighten up" because it is much harder to cut, drill, mill, turn, etc. But, you do get more lbs off for your increased work time.

It is all about tradeoffs.

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

I happen to know ;)... AND
It is listed in the Chassis documentation found here:
http://www.ifirobotics.com/kitbot.shtml

The chassis is made from 5052, H34 Aluminum.
Great stuff, welds niiiiiice.

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

How do you figure it's a tradeoff? You're saying a steel robot (or component) would get more pounds off in the lightening phase, but wouldn't it be far heavier to start off with anyway?

Let's say the aluminum robot I wanted to make would be 150 pounds before lightening. If I were to make a functionally identical robot with steel, it would weigh 250 pounds (the ratio of aluminum to steel's weight of course varies, but it's generally between two and three times as much). Now, bearing in mind you will be able to put a few more holes in the steel robot or use thinner steel, the strength gain from steel (and don't forget in addition to this the higher cost and machining time) would not be enough to use appreciably less material.

In other words, this is no tradeoff, but is very one-sided in aluminum's favour. Bearing in mind this example is a bit impractical in a robot-building sense, a square-inch hole in a steel plate versus a square-inch hole in an aluminum one will obviously not bring the former's weight below the latter's. Which is probably why most everyone uses aluminum on their frames I would say.

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.