Steel on a FRC Robot

[kgzak]

How many people have seen steel on a robot? I'm just wondering because our whole lift is pretty much made of Stainless Steel. I've wondered if people have thought of using this as a solution to making things more rigid and stronger. I'll see if I have a picture of our robot to show you.

[DarkFlame145]

I have been told that back in the day, steel was mostly used. I have seen a couple of my High School's team's old robots made of steel. I find it interesting your team used stainless steel. It's not cheap or light stuff.

[KleinKid]

At first our arm support across the top was made out of aluminum but after testing (picking up a chair) with our claw we noticed that we bent it by several inches. We replaced it with a steel bar and haven't had problems picking anything up that weighs less than 20 pounds.

[Grim Tuesday]

I can't imagine making anything out of steel on our robot (besides some drivetrain components)

On our elevator this year, we even replaced a steel axle with an aluminium one to save weight!

[Alpha Beta]

I've been wondering if steel on the end of a robot arm would accidently attract a magnetic mini-bot this season. It would be humorous and unfortunate all at the same time to see a big robot try to shake off the little guy.

[theprgramerdude]

Originally Posted by Alpha Beta

I've been wondering if steel on the end of a robot arm would accidently attract a magnetic mini-bot this season. It would be humorous and unfortunate all at the same time to see a big robot try to shake off the little guy.

Id wager that we might see that happen at least once for every regional: one team accidentally get inside anothers frame perimeter, and takes their minibot away. Now that I think about it, it might be a semi-valid strategy for finals

[kgzak]

Originally Posted by DarkFlame145

I find it interesting your team used stainless steel. It's not cheap or light stuff.

All of it was donated to us by Oliver Products (Our mentor works there). we also found it to be strong enough that we don't need much to make a strong lift and with the thin wall we are using it would weigh less than the equivalent of using aluminum. We are doing a scissors lift so we are using round tubes. I'll get the specs on the tubes tomorrow (Diameter and Wall)

[Joe Schornak]

Our robot has an all-steel welded frame, and it's worked quite nicely so far. Although steel is indeed heavier than aluminum, we make up for it by using thinner-walled material and very few bolts.

The trick with using steel is to take advantage of its greater strength. We're able to save weight by using many fewer supports than we would have with aluminum. Our frame is basically a flat rectangle, solidified by some diagonal corner brackets. It comes out a bit heavier than the aluminum equivalent, but it works nicely as a counterbalance for the elevator. The whole robot weighs 119.2 lbs, and is able to complete every element of Logomotion.

There are still many aluminum parts on our robot. Things that really need to be lightweight, like our gripper and minibot deployer, and things that aren't in high-strain positions are vastly aluminum. Our in-house machined components are also primarily aluminum, due to ease of work and speed. It is simply a matter of weighing pros and cons.

Steel's good to use in FRC, as long as you have the proper tools and skills at your disposal, and plan carefully. I suppose that magnetic minibots could be an issue... ours uses a fairly powerful neodymium magnet, and we haven't gotten it stuck to the frame yet. Yet...

[kgzak]

Last time we weighed to robot it was around 112 but we still had parts to put on. then we realized we had the battery on so we are still in a good position. still waiting on minibot deployment (less than 8 pounds) and we took off 22 pounds for our claw/lifting mechanism.

[Tristan Lall]

I'm not a fan of ordinary structural steel for FRC robots. The strength to weight ratio is awful, and the available sections are generally inconvenient. You see it occasionally, and you always wonder what set of design tradeoffs made that worthwhile for the team. (To be completely blunt, it's probably more like a lack of design that precipitated it.)

Alloy steels, particularly chromium-molybdenum steels like AISI 4140, are very useful, however. In the annealed condition, the strength to weight ratio is around the same as AA 6061 wrought aluminum. The difference is that you can weld annealed AISI 4140 with negligible loss of strength, while AA 6061 will drop dramatically in strength when welded. That makes welding a viable construction method for high-stress, high-strength parts.

The trouble is, because the steel weighs more, you have to use thinner material. This can be difficult to work with. Also, since 4140 typically comes in solid and tube sections (and doesn't work very well as sheet metal), you'll see it used in space frames, rather than stressed skins.

And of course, steel (of all kinds) is stiffer (in terms of elastic modulus) than aluminum, so when distortion is a major criterion, you may want to choose it.

But as for stainless steel, I've got to ask: why? (There are lots of grades of stainless, but in general, while it's probably a slightly better material than structural steel for an FRC structural application, it has a lot of other undesirable properties—for instance cost and machinability, under most circumstances—that make it a surprising choice.)

[Billfred]

We used a little bit of 1/8" thick flat steel on the end of our arm; originally we intended to tap its magnetic properties for a little extra holding force to keep our claw steady, but we decided to go with an active mechanism later down the road. Beyond that, it's pretty much fasteners.

[Dancin103]

Originally Posted by DarkFlame145

I have been told that back in the day, steel was mostly used.

That it was, but now I can't see using steel, maybe to reinforce something like some one else was talking about, but I can't see someone taking and making a robot entirely from steel, that's just nuts.

Just my two cents.

[ratdude747]

in 2009 my former team, 1747, used a steel shaft for their shooter. i remember the aluminum one having too many holes/vibrations and having to machine a a steel one to replace it. luckily, steel fixed it.

[548swimmer]

We have a small amount of 304 stainless on our robot because of the strength and package requirements for part of our arm. We also use steel shaft for the driveshaft of the arm.

[kgzak]

Originally Posted by Tristan Lall

for instance cost and machinability, under most circumstances—that make it a surprising choice.)

as I said for cost, it was donated (I am assuming they use stainless for what they do and said we could use some) and we didn't machine it all so we didn't have issues with that. With the load on it we need something stronger than aluminum. Stainless steel was what we had available so we used it.