Steel Frame

[charlie1218]

1218 has been using 8020 since our second year and it has been wonderful to us. While we could do a welded aluminum frame, we often find ourselves making HUGE changes in the end of the build season. Plus, it provides so much flexibility and is easily reusable and i is easy to prototype with. We have learned the art of lexan, 8020 and luan (where needed). Its all about what fits your needs, and we have some crazy ideas that wouldn't work without 8020

[mark johnson]

Originally Posted by silv940

I don't understand the question

Normalizing in simple terms is post heating the weld to relieve stress from the weld process. Actually when you weld chrome moly tube you should pre and post heat the weld joint but i know alot of chassis builders that do not and have no problem. Another way you can normalize the frame is to totally finish the frame , drill tiny holes by each weld joint and have the whole frame heated in a oven , this will take out all stresses built up by the welding process.

[MrForbes]

thanks for explaining that

Did some more welding. The transmission and chain tensioner mounts are welded to the top of the frame, the axles to the bottom. Center four axles are welded to 1/8" thick plate, the plate is welded to the frame, to drop them down a bit for easier steering.

[sgreco]

I must admit I'm a little confused...Why add unnecessary weight? Just because you can't weld aluminum doesn't mean you shouldn't use it. Rough estimates would say steel is about 3 times the weight of an equivalent piece of typical aluminum. So with 1/16 inch wall steel, and 1/8 wall aluminum you have half as much volume with the steel. So for a size that would weigh 16 pounds in aluminum, the same volume will weigh 24 pounds in steel. Do you really want to waste that much weight into a frame that's strength would suffice in something that is much lighter. Plus the fact that you can also use 1/16 aluminum in places of low contact. My team used half 1/8 aluminum and half 1/16 and we never had any problems at all. True we welded it, but there are certainly ways to bolt aluminum that are very structurally sound and are still much lighter than welded steel. It's your call though. There are some advantages to steel as you mentioned, but I don't think the added weight is worth it.

[MrForbes]

The assembly shown has support for the wheels and transmissions, and weighs under 12 lbs.

If that's too heavy for your robot, then you should definitely use something besides steel!

[Dick Linn]

Jim,

For this particular configuration, I don't blame you for using steel. The stiffness:weight ratios of steel and aluminum are pretty close. They you have to consider the section. Plus, it's a lot easier to weld steel axles on steel tube.

[Al Skierkiewicz]

Jim,
We have used steel in the past. One of the drawbacks was the ability to rework in the pits. It's tough to drill speed holes in the steel frame to loose weight and drilling takes more time when you need to mount something. If you have the weight, which this year's game seems to allow, then you should have a workable frame.

[Chris Fultz]

8020 can be a great frame material also.
The key is to make sure connections are tight and stay tight.
Some nylon insert screws, or the removeable locktite is a good solution.

Every material choice has pros and cons - the key is to determine your specific needs and capabilities, and make the best of your choice - whichever material that is.

[,4lex S.]

Rough estimates would say steel is about 3 times the weight of an equivalent piece of typical aluminum.

Not exactly. I believe (don't hold me 100% to this, I am only in 1st year material science), the most important characteristic for a FIRST robot framing material is the specific stiffness [Elastic Modulus (willingness of the material to bend)/ Density]. Steel and Aluminium are pretty much equivalent in this regard. Still, you can get a more durable frame out of aluminium, for equivalent weight.

If you have the weight to spare, it is a cheaper (and easier to fabricate) solution, and cost is a real world parameter that many teams have to deal with.

[Steve Kaneb]

Originally Posted by Dick Linn

Plus, it's a lot easier to weld steel axles on steel tube.

That's what brazing is for. 190 has parts from our '99 swerve drive that are brass->steel, and they've held up remarkably well. Brazing is also excellent with aluminum->steel.

[billfunk29]

We have a prototype steel frame. 1x1x16ga.
No test data yet.
Check out Wellnuts for attaching things.
http://www.hansonrivet.com/w71.htm

We are also using a Flowdrill for tapped holes. My 1.5hp bridgeport will work a 10-32 flowdrill, if I spot heat with a torch just before drilling.

To get equal durability from aluminum we would have had to heat treat after all the welding. Didn't seem practical.

[MrForbes]

Thanks for the comments, they are all appreciated.

I put the bare frame (as shown in the photo in my previous post on the postal scale in the shop...10.5 lbs.

We worked today on figuring out how the ball handling mechanisms will fit, and will probably add an upper frame made of the same steel tubing, which will add about 12 lbs, for a total frame weight of under 24 lbs. This is about the same as last year's plywood robot. I think we're doing OK, since we don't see how we can get much weight in the mechanisms this year. I guess if you have 80 lbs of stuff "on top" then the extra 5(?) lbs that steel adds would be a problem.

[MrForbes]

latest update. We added the top of the frame, which forms the surface that will support the bumpers. It will also support the kicker at the front, and probably some other stuff like an arm if we ever figure out what that is.

I think it should weigh right around 21 lbs as it sits. If you don't like the material, perhaps the design, done in aluminum, might work for you?