Chief Delphi - Steel on a FRC Robot

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- Technical Discussion (http://www.chiefdelphi.com/forums/forumdisplay.php?f=22)

- - Steel on a FRC Robot (http://www.chiefdelphi.com/forums/showthread.php?t=92821)

pfreivald

23-02-2011 22:12

Re: Steel on a FRC Robot

Maria -- our 2011 Logomotion Robot -- has a 1/2" stainless steel rod as the main support for her arm, and 3/8" steel rod elsewhere (in bronze bushings) for structural pivot points.

In previous years we have always used 3/8" steel rod for our axles.

tutkows1

23-02-2011 22:14

Re: Steel on a FRC Robot

Last year my teams robot was made complete out of angle iron steel, and this year our part of our arm is stainless steel.

Zholl

24-02-2011 01:04

Re: Steel on a FRC Robot

One of the axles on our claw mechanism is currently made of steel, mostly because the aluminum rod that was in there before kept bending under load. Otherwise, it's aluminum and a wooden board

MrForbes

24-02-2011 01:08

Re: Steel on a FRC Robot

Last year we made our chassis of MIG welded thinwall mild square steel tubing. It's strong, a bit heavy but not too bad, and it's relatively easy to build. Also it's locally available and not very expensive.

We also make the Typewriter Repairmen underwater ROV frames from steel strap, for similar reasons. A coat of spray paint keeps it from rusting.

If you do a good job designing your manipulator to be light, then a bit more weight in the chassis really doesn't hurt anything.

Hawiian Cadder

24-02-2011 01:48

Re: Steel on a FRC Robot

last year the drawback for our kicker was a pair of wheels with a little pins to drive each other, this needed to be made out of steel because we did FEA on the part and aluminum was not strong enough, an aluminum part on a high torque part must be made larger to offset the torque. steel can be made smaller and thus easier.

s_forbes

24-02-2011 04:29

Re: Steel on a FRC Robot

2840 made an appearance at the Duel in the Desert and was sporting a steel chassis, so I know of at least one steel framed robot this year.

Steel is a great building material... cheap, easy to work with (if you have a mig welder and a chopsaw). It ranks up there with wood and fiberglass in terms of my favorite robot building material.

JamesCH95

24-02-2011 07:22

Re: Steel on a FRC Robot

Quote:

Originally Posted by Tristan Lall (Post 1030294)

I'm not a fan of ordinary structural steel for FRC robots. The strength to weight ratio is awful[...]

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.

4130 steel is available in many tube cross sections with very thin wall thicknesses, down to 0.035in. If one was going to make structures out of steel that's what I'd recommend. I'd then advocate the use a weld-in nuts to fasten everything to the frame.

flippy147852

24-02-2011 07:55

Re: Steel on a FRC Robot

I know in the past 1918 has used steel bars as ballast to get weight where we want it

SGS	24-02-2011 10:03

Re: Steel on a FRC Robot

Our whole forklift/arm is made of steel, completed the arm weighed about 30 lbs, and ultimately caused our robot to weigh about 124. We had to disassemble and cut holes in everything, but our robot is VERY robust.

Last year, our whole frame was made of 1' square steel tubing , it was the only tunnel robot near the weight limit, but in the finals at Lone Star, it was an indestructible defensive robot and still quite fast.

Granted steel may not be the best material, but it is often a practical option and it is possible to create a decent if not relatively good robot with it.

JVN	24-02-2011 10:52

Re: Steel on a FRC Robot

Quote:

Originally Posted by kgzak (Post 1030225)

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.

We rely on the strength of our cross sections rather than the strength of the material itself. If you do this correctly you can produce very light mechanisms made from very thin material that are extremely strong.

In my mind, the only reason to go a different route would be lack of resources.

-John

Jared Russell

24-02-2011 10:57

Re: Steel on a FRC Robot

Has there ever been an FRC robot that didn't have ANY steel? (other than whatever is contained in the required electrical components, ex. the cRIO chassis)

I suppose you could build a bot with all aluminum fasteners, all aluminum gears, all aluminum shafts, no chain, etc., but has it ever been done?

MrForbes

24-02-2011 11:17

Re: Steel on a FRC Robot

Quote:

Originally Posted by JVN (Post 1030595)

Which is one of the factors that drives most teams to make their robots differently than team 148 does.... :o

Karibou

24-02-2011 12:16

Re: Steel on a FRC Robot

I think that the only steel parts that we have this year, fasteners and gearboxes aside, are our axles. We used 1/2" steel hex shaft in 2008, and we are using them again this year. We tried switching out the steel axles for aluminum ones in Pittsburgh in 2008 for weight (even though we were slightly underweight already), but quickly switched back after one of the aluminum ones sheared during a match and we had to pound half of it out of the wheel with a mallet.

Jeff Waegelin

24-02-2011 15:19

Re: Steel on a FRC Robot

I built a whole robot out of steel once, in 2002. The frame and manipulators were all steel. Granted, the whole robot was 12" tall, with a pair of 30" extending arms, and that was it, but for what we were doing it did the job and made the robot a veritable tank. It was mostly because we had steel welding capability, but not aluminum welding that year.

Since then, I've never used steel for anything outside of shafts, fasteners, or ballast.

kgzak

24-02-2011 15:27

Re: Steel on a FRC Robot

Welding aluminum is just as easy as welding steel for our team (metal shop down the street) so aluminum makes a lot of sense for our robot. It's hard to add support vertically to a scissors lift so we need the stronger material.

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