Steel Frame?

[gburlison]

Last year we found it difficult to get the aluminum 'C' channel that we wanted for our frame. This year I was thinking about using steel 'C' channel that is used in steel framing. It is available in sizes that are comparable to lumber and thicknesses from 12 to 20 Gauge (about 1/32 in to 3/32 in). In the past we have used aluminum 'C' channel with a thickness of 1/8 inch and had good success.
Has anyone used steel 'C' channel on their robot?
What do you think of this idea?

[MrForbes]

Steel is heavy, and kind of flimsy in any thickness that's close to the weight of the aluminum you've been using. Steel is about 0.283 pounds per cubic inch, aluminum is about 0.10 pounds per cubic inch.

We've done well with pultruded fiberglass, it's about half as dense as aluminum, and the 1/4" thickness is very strong and resilient.

[CraigHickman]

Ew, C channel. We use 1x1 box extrusion. It's been plenty strong, easy to weld, and nice and cheap/available.

Why C channel?

[Scott Morgan]

We used square steel tubing for our frame in 2003, I'm not sure why, but I think it was because we didn't have the resources to weld aluminum.
I wouldn't recommend using steel because it will eat up your weight budget pretty quickly.

[Gabe]

In my experience c-channel twists and torques (annoyingly so) making me turn to regular tubing. What's wrong with rectangular, round, or square steel tubing?

[=Martin=Taylor=]

I built a table for a 400 lb. mill out of 1/32" 1X1 steel tubing last summer. Yes, I used a lot of cross braces. But it was both light and strong.

The only reason I used steel was because I already had it, and didn't want to spend the money on aluminum.

As for aluminum C-channel. I don't think it's that hard to find. We always get some 1/8" wall 1" interior stuff that we can hammer 1x1" tubing into. By doing this we don't have to worry about clamping the frame when we weld it. This saves time, and clamps... :)

[gburlison]

Ew, C channel. We use 1x1 box extrusion. It's been plenty strong, easy to weld, and nice and cheap/available.

Why C channel?

We have used C channel for a couple of reasons.
Two 1x1 box extrusions used on the side of a frame is heavier than a 4x1 C channel.
We have had good results bolting together a C channel frame and do not have the ability to weld aluminum.

[EricH]

We have used C channel for a couple of reasons.
Two 1x1 box extrusions used on the side of a frame is heavier than a 4x1 C channel.
We have had good results bolting together a C channel frame and do not have the ability to weld aluminum.In that case, I'd take squirrel's suggestion about pultruded fiberglass. Talk to 842 and 1726 about their frames. (And you don't need a 4" tall frame, do you? 2" should be fine...) Or go to 80/20, which several teams have used in the past. Steel is not a nice thing to have on a robot frame for weight reasons.

[MrForbes]

Actually a 4" tall frame has some interesting advantages....but following a strict weight budget (for the rest of the robot) is required.

Here's a look at how the frame can be layed out, the I beam is a neat shape for the sides, wheel mounting is pretty simple with just a 3/8" bolt for each axle going thru holes drilled in the fiberglass frame.

The 4" high 1/4" thick wall around the outside of the robot is incredibly tough, no bumpers needed, but bumpers can be attached easily. The drivetrain area is open so it's easy to work on, yet the chains are protected from damage from colliding with other robots.

One downside to this material is the limited availability...think truck freight and a bit of a lead time, and a quantity purchase. I think it might be easier to just find some aluminum C channel, if you have a design that could get by with it. Spacers between sections of channel would make a reasonably strong structure, with good accessibility compared to rectangular tubing.

[gburlison]

In that case, I'd take squirrel's suggestion about pultruded fiberglass. Talk to 842 and 1726 about their frames. (And you don't need a 4" tall frame, do you? 2" should be fine...) Or go to 80/20, which several teams have used in the past. Steel is not a nice thing to have on a robot frame for weight reasons.
Yes, I mean a 4 in tall frame. When I say a 4 in tall frame, I am talking about the entire side of the robot, minus anything that might be bolted on top (like an arm) that would be used to play the game. Take look at this picture
http://www.chiefdelphi.com/media/photos/19828

[MrForbes]

Another approach if you can' find the aluminum channel you need, is to make it from sheet. All you need is to find some place that has a good (heavy) sheet metal brake. Also it helps to use a soft grade of aluminum, and to practice bending first on a smaller piece. And if you first bend another strip of metal, and put it on the fingers of the brake, then you can bend a larger radius and it will be stronger.

[Tytus Gerrish]

a robot made of steel is still a robot. if you have somone who's skills in fabricating steel are well refined you can definetly make a lightweight sturdy robot using steel. Steel has been used for hundreds of years by many cultures, industries, nations and handymen. the weight and streignth of aluminum and steel is nearly proportional as steel is about 3 times stronger and 3 times heavier than aluminum. steel is reputedly easier to weld, less prone to melting, bending and harder to sctratch. being less expensive than aluminum as well also offsets its tendency to oxidise into rust.

[MrForbes]

I agree with Tytus, although I'll add that when you design using steel, you should probably design the robot differently than you would with aluminum. See if you can find pictures of 1501's robot from the 2007 season.

edit: look at the pictures on the lower half of this page, the steel tube frame of the 1501 robot can be seen

http://photos.project1726.org/thumbnails.php?album=21&page=6

[Qbranch]

If you REALLY REALLY want C (or U) channel, McMaster (http://www.mcmaster.com/) has it as usual (example, part# 1630T13). I have to suggest square tube... its very strong+light.

If you have access to a CNC mill (and a pipe bender, though it's not completely necessary) you can also try round aluminum tube (available everywhere pretty much).

I know 1501 was very successful with their steel frame lifterbot this past season... sorry our robot was too long for your amazing elevator!

-q

[Gdeaver]

Mc Master also has the fiberglass pultrusions. Part # 8529K63 The pultrusions are listed under plastics -> fiberglass. Sold in 5' lengths - UPS friendly.

[MrForbes]

Thanks for letting us know about McMaster stocking fiberglass! although they don't have our favorite 4" x 4" x 1/4" I beam.

[Dick Linn]

Has anyone ever built a frame from extruded aluminum ladder rails? Just curious.

[EricH]

Has anyone ever built a frame from extruded aluminum ladder rails? Just curious.
Does building an arm mount from a COTS ladder count? There was a team at Davis 2005 that did that. (Almost that whole robot was either KOP or COTS household items.)

[MrForbes]

I think I've seen ladders used on two robots, the one Eric mentioned and also the Sporks in Arizona this year.

Not for a frame, though. I expect it would work, you could just screw a flat plate across it to mount transmissions, etc.

Could even use a fiberglass ladder :)

[=Martin=Taylor=]

Has anyone ever built a frame from extruded aluminum ladder rails? Just curious.

http://www.team847.com/coppermine/albums/userpics/10001/normal_regionals07_2.jpg

Yes. There was also a team at Davis last year that had a ladder arm.

[Billfred]

And back in 2005, there was our districtmates 1398 (http://student.project-real.org/slideshows/050222ship/PW02.htm).