Is steel a recommended material for extentions of base kit?
If it works well and you can afford the weight (or need it to be a certain strength while remaining thin), then it’s a fine material. It would be surprising if you couldn’t solve the same problem with aluminum with less weight.
I recommend that if you use steel anywhere on your robot, use a small amount. You’ll hit your 120 pound weight limit pretty quickly.
Steel is very useful stuff. I prefer fasteners made of steel to those made of any other material. Motor cores should also be made of steel.
Aluminum is better for large, thick parts.
You’ll have to be more specific. What do you mean by “extentions of base kit” ? Do you want an arm to extend outside your robot or make your kit bot frame larger or something else? Also “steel” comes in many alloys and tempers. I wouldn’t buy a plate of tool steel to make my kit bot larger.
Almost all metal for FRC is usually aluminum of some sort. However, there are some applications where sometimes steel is preferred, notably in high torque gearboxes, shafts, keys, chain, and shifting mechanisms, although there are people who have accomplished this with aluminum as well. Also, many common fasteners are zinc-plated steel (or some other type of steel), so unless you want to specially source your fasteners, you’ll probably use a lot of steel on nuts-and-bolts stuff.
There are some teams who have, often due to unavailability of other metals, built most of their robots with steel. Theoretically, both aluminum and steel can be used to make a great robot, it’s just a matter of knowing how to use each material properly and in what situations. That being said, in practice, most often aluminum will be your best bet, especially with large robot parts (because steel is HEAVY), but this sometimes a flexible rule.
EDIT: What Mr. Wallace said about motors applies as well. You won’t find many motors in FRC made of aluminum. Additionally, there are many types of both steel and aluminum, so selecting specific alloys and tempers can be important in addition to the steel vs aluminum debate.
We have used steel in very high Stress applications but it all comes down to weight. Also watch what alloy of aluminum you are using is that will play a role.
If you DO plan on using steel as structure, I would recommend keeping close tabs on weight as you build. (I recommend keeping close tabs no matter what, but more-so if you use steel) I remember a rookie team one year coming with a robot with a large steel superstructure that weighed in on practice day at around 300 lbs. :ahh:
It’s all in the design. Aluminum isn’t as much lighter than steel as you might think. It’s only 30% the density, but it’s (generally) only 50% as strong, so you can afford to use smaller pieces with steel. The ratio of strength to density is called “specific strength”. For instance, a 0.75" x 0.75" x 0.065" (thin) wall tube is roughly as strong, a little less stiff, and only about 30% heavier than a 1" x 1" x 0.095" wall 6063 aluminum tube.
Welding (most grades of) aluminum takes away half of its strength, whereas mild steel stays relatively constant, so the steel welded frame would end up slightly stronger. Plus any hack with a mig welder could weld steel for you, compared to aluminum where you need a TIG welder and a decent amount of experience. Steel is a heck of a lot cheaper than aluminum too! These are good reasons to give (thin wall) steel a careful look.
My boss has a similar opinion when he was mentoring a team. He loved teaching the students how to weld up their frames. He was also mildly surprised that they were always very close to over weight. My primary arguments against him were that steel is a fair bit harder to cut and drill, and its difficult to get sections with walls thin enough to be comparable to aluminum. Getting something equivalent to 1x1x1/16 aluminum is not easy. And we’ve used smaller than that for lightly loaded structures before.
Our lightest robots ever have had full steel superstructure built from 1/2 inch square steel tube. In 2011 we were ~85 lbs. and in 2013 we were right around 105 lbs.
We found that with a steel frame we used so much less material for the same strength.
Another benefit is when you hit something wrong, you just bend it back. Aluminium sure doesn’t play as nice in that regard.
We use aluminum alot now simply because so many nice COTS items interface with common aluminum extrusions.
Another feature of steel is that lots of folks can weld it, even me! and I have little skill.
We have made two robots with steel frames. As mentioned, you want to use relatively thin steel…16 gauge square tubing is good, and easy to find. But also as mentioned, we don’t know what it is you’re trying to make, exactly. Sketches are very helpful when asking questions like this.
btw, most cars have been made mostly of steel for about a century. It works.
Just like everyone else has said, aluminum is the preferred material for the vast majority of FRC teams, because it’s much lighter than steel and very easily accessible. Although steel is MUCH easier to weld, aluminum is easier to cut, drill, etc, and pretty much any FRC product you get off-the-shelf will be aluminum.