Chief Delphi - Types of Metal

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Re: Types of Metal

We on 33 have been doing a folded sheet metal chassis for the last few years. Once you learn how to work with sheet, it is pretty easy, very light and very effective. You do need to learn rivet techniques and how to bend metal accurately an effectivele. We use heat treated 6061 T6. Before everyone tells me you can't bend it, that is not true. Heat treated (T6) means you need to be very careful bending it and use an ample radius.

For the big structures we have generally been going with space frame welded aluminum tubing both square and round. I have a lot of race car chassis construction experience so it helps. One of our students did most of the welding this year. While she is not a pro, she gets the job done.

What material you decide to use depends on budget, equipment, and skill sets. 80/20 or Star bar is very easy to use but extremely heavy (from a KB33 perspective). 1/16" is the beefy stuff on our machine and we often go down to 0.035" wall round tube.

If you do not have a skilled welder, I would recommend visiting the Team 1216's website and check out their chassis. The pre-drill 1x1x1/16 box with a very specific hole pattern. This technique gives 90% of the strength of 1x1 box with the flexibility of Star-bar or the kit rails with a TON less weight. These guy are pretty modest and only went to 1 regional so you won't see a lot of buzz about them. As a structures guy, I have a lot of repect for this technique as it has the 4-way threat of strong, lightweight, flexible design, and easy to use/manufacture.

Another good source are the 2 "Behind the Design" books. You can almost tell what line of work the sponsors are in by the construction of the robot. With aircraft companies you will see a lot of sheet metal. Nasa and Robotics related sponsor teams seem to have a lot of CNC. Big 3 teams seem to have a lot of welding.

As far as material sponsors to order from Aircraft Spruce has an awesome selection but can be a bit slow to certain areas. They have some truly amazing materials line a strut material that is 11oz. for 8 feet. Online metals is a good plae to order small quantities, but were extremely slow on their delivery for us (I did find a way to expedite future orders). Mcmaster Carr is fast but expensive.

Re: Types of Metal

I was mistaking 80/20 for starbar.

Re: Types of Metal

ttldomination,

I sent you a pm. Just get in touch with me and we'll discuss some things.

Re: Types of Metal

Bleh, the less 80/20 that's used on a bot the lower my blood pressure is. It leaves too much room for last-second decisions that haven't been thought through.

We've used 1/16 wall 1x1" 6061 Aluminum tubing for our frame for 3 years now. It's always been welded. We have students that practice welding on our prototype frames, then they assist the pros who do the welding of the actual frame during build season. From there the frame goes straight to powder-coating at the same sponsor, which also adds strength and rigidity to the frame.

Our drive base frame this year came out to 6.1lbs after powder coating, and had zero CNC work or cheese-holes added to it. In future years we will probably experiment with 1"x1/2" tubing that has a 1/16" wall and sturdy injection foam in order to produce a more compact frame.

Re: Types of Metal

1501 has used Chromolly tubing on our past two robots. It's light and strong. We gas weld it, but I believe you can use better methods of welding.

Re: Types of Metal

Quote:

Originally Posted by squirrel (Post 750294)

80/20's main advantage is that it requires little effort to make many different designs with it. It is not a very efficient shape as far as it's strength/weight ratio.

If you want to spend more time designing, you should look into using many other sections of aluminum, as well as other metals and non-metals. Steel can be very effective (look at 1501's 2007 robot), sheet aluminum is also used by them to make strong, light structures. We've used fiberglass pultrusions for our frame, and 842 uses it for their entire robot! Some teams use plywood, you could use spruce, or other woods, which take some effort to design but are relatively easy to work with and can be very strong and light (think of the early airplanes, which were made almost entirely of spruce). For aluminum, look into tubing, both round and square, and angle and sheets. Our robot used sheet and angle aluminum this year.

Also look at the various ways you can connect the parts. Rivets are great, they are light, strong, and quick to replace if needed. Bolts and nuts are a bit heavy and cumbersome, but can be removed and replaced many times. Glues are a bit tricky to apply and hard to repair joints made with them, but for some joints they are the best way to go. Welding is great for thicker alumimum parts, and for thinwall steel tubing (such as 1501 has used).

we use the same stuff as 842 (that and PVC was almost our entire robot this year). We even buy it from the same place and we love it. I really hope more teams use it its great.

Re: Types of Metal

Quote:

Originally Posted by Lions for First (Post 750627)

we use the same stuff as 842 (that and PVC was almost our entire robot this year). We even buy it from the same place and we love it. I really hope more teams use it its great.

What place do you buy from, and how much does it typically cost?

Re: Types of Metal

Quote:

Originally Posted by cooker52 (Post 750502)

1501 has used Chromolly tubing on our past two robots. It's light and strong. We gas weld it, but I believe you can use better methods of welding.

Amen. I would love to see more teams use chromoly.

Re: Types of Metal

Quote:

Originally Posted by cooker52 (Post 750502)

1501 has used Chromolly tubing on our past two robots. It's light and strong. We gas weld it, but I believe you can use better methods of welding.

I'm not sure that you aren't using the best method already. Most of the best bicycles in the world before the advent of aluminum in the late 1980's were made out of brazed chromoly. Gas welded or brazed joints in 4130 chromoly should be at least as strong as the tubes themselves. It would be interesting to build a competition robot frame using full racing bike chromoly techniques, with butted tubing and even lugs in the joints. I understand that metallurgical advantages mean that welded joints work just as well as lugged and brazed joints, but it would certainly look old-school cool... :]

Re: Types of Metal

I'm pretty sure that 1501 welds their tubing, instead of brazing it.

Re: Types of Metal

What, exactly, is "ITEM?" I can't just google it cuz I get a million results about video games.

Our team has been extremely reliant on 80/20, with 1'' tube stock where we need to decrease weight. We're building a new robot cart this summer, and I was wondering what you guys would suggest to carry a much heavier load than a FRC robot would be expected to stand up to. Most of the guys are leaning towards 80/20, but I'd rather avoid it because of cost, durability, and weight.

Also, where do you get chromoly?

Re: Types of Metal

Quote:

Originally Posted by m3ch4num470r (Post 750953)

It's very similar to 80/20, with a few minor differences in features, but overall, it's going to have the same durability/weight. The cost may be a little cheaper, but I'm not certain about that.

http://www.item.info/en

Re: Types of Metal

Quote:

Originally Posted by Richard McClellan (Post 750954)

Its also metric... Which would make it annoying to use.

Re: Types of Metal

Quote:

Originally Posted by Hachiban VIII (Post 750966)

Its also metric... Which would make it annoying to use.

Don't tell the Canadians that...

-Vivek

Re: Types of Metal

Quote:

Originally Posted by m3ch4num470r (Post 750953)

Also, where do you get chromoly?

here's one way to find this type of stuff...

http://www.google.com/search?hl=en&q...=Google+Search