which is better aluminum or steel????

[[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

[N7UJJ]

Originally Posted by SCYTE16

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

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!

[[527]phil]

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.

[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

[Not2B]

Originally Posted by Andrew

How come no one talks about riveting? Yet another alternative to welding (permanent) and bolting (removable but heavy).

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.

[Hunter]

Originally Posted by Not2B

We riveted this year, and we loved it.

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.

[Not2B]

Originally Posted by Hunter

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.

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

[sanddrag]

Originally Posted by Andrew

How come no one talks about riveting? Yet another alternative to welding (permanent) and bolting (removable but heavy).

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.

[Captain Rich]

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?

[Cory]

Originally Posted by Captain Rich

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?

something in the 7000 series, I think.