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.