What types of metal do you use for your robot in general?

[Team3844]

We use stainless steel for 90 % or more of our bots construction. Our major sponsor manufactures commercial dishwashers. 3 years ago they volunteered to laser cut and fold all of our sheet metal with one condition, it had to be stainless steel so they could nest it in with their regular production. We use primarily 1/16 " I think 14 gauge with 1/8" 11 gauge for high stress parts. It makes a pretty bot. They usually make us 3 to 4 times the parts we need so we have a big collection of spare parts. I know most of you think the weight would be an issue, but by using thinner gauges and Swiss cheering at the design stage we come in comparable to aluminum. 105 lb in 2014, 120 lb 2015 mostly caused by a long wooden ramp and a over engineered lift, and 111lb not this year.

[GeeTwo]

Attempting to synthesize all of the responses, it seems to me to come down to:

1. Take advantage of your expertise. Whether it's woodworking, monocoque, steel, sheet metal work, fiberglass, carbon fiber, or whatever, leverage it. Experts in any decent material can out perform people trying to wing it in the best available material. If you are so lucky as to have experts in multiple materials, may I suggest a bake-off? (and express a bit of envy, as well)
   
2. If your team does not have real mentor expertise in a construction material, aluminum (6061, 6063, 7075 extruded and tempered or 5052 sheet/folded) is a good place to start, with baltic birch plywood and sheet steel as alternates when aluminum doesn't fill the bill.

[Poseidon5817]

Originally Posted by Team3844

We use stainless steel for 90 % or more of our bots construction. Our major sponsor manufactures commercial dishwashers. 3 years ago they volunteered to laser cut and fold all of our sheet metal with one condition, it had to be stainless steel so they could nest it in with their regular production. We use primarily 1/16 " I think 14 gauge with 1/8" 11 gauge for high stress parts. It makes a pretty bot. They usually make us 3 to 4 times the parts we need so we have a big collection of spare parts. I know most of you think the weight would be an issue, but by using thinner gauges and Swiss cheering at the design stage we come in comparable to aluminum. 105 lb in 2014, 120 lb 2015 mostly caused by a long wooden ramp and a over engineered lift, and 111lb not this year.

We're pretty close to the same as you guys, main sponsor works in stainless sheet metal, so we do too. I think we used entirely 18 gauge, except for our shooter wheel mounts.

[LCJ]

We did a pretty unique construction style this year.
For the drivebase we used large plates of 5052 sheet metal supported by 0.5x0.5" with 1/16" thick wall aluminum tubes riveted on at the edges.
The reasoning is that our team, where we machine everything in house, doesn't have access to a precision CNC break. We can't bend sheet metal accurately enough to construct a chassis out of it so we just riveted on tubes at the edges to strengthen the plates.
The shooter was constructed using 1x2" VersaFrames and lots more of 5052 plates, riveted together so that the channels were again at the corners and edges of the large plates.
Different student on the team have different design styles so our robot ends up looking pretty radically different each year (just my design style changed from 1x1 VersaFrame everything to 1x2 and large plates this year).

[maxnz]

We used 1 1/4" c-channel for the majority of the build, but used the 1" tubing from the KOP for our arm. We did use a small part of the end plate of the KOP chassis, but otherwise, just c-channel.

[hrench]

I think it's pretty fun that I kicked off a new branch of robot material selection here with my advocacy of steel robots. I was at a regional so I didn't get to participate in the conversation over the weekend, but here's a few words:

Originally Posted by JesseK

Ooh, ouch. Those are fightin' words....

Oh, you know this was meant in the friendliest spirit...1108 has built some rickety riveted robots. I know that airliners are aluminum riveted and they do pretty well, but not with pop-rivets.

Originally Posted by mman1506

Yeh, 1114's robots are always soo rickety and wobbly /s

1114? Are they any good? (Joking, of course they are) Yes, aluminum is a great material.

Originally Posted by ratdude747

Have you ever considered MIG or TIG as an upgrade down the road?

We'd love to have mig or tig, but the welder is my personal welder and a bottle is $150 or so, plus $50 to refill. Mostly we grind the surface of the welds to remove spatter, but with kids welding, grinding the surfaces to make them smoother would probably be helpful anyway.
Probably yes, we'll move up sometime.

Originally Posted by Captain_Kirch

Agree to disagree here. Aluminum is lighter and we use more of it.

Actually, I should mention that I'm an advocate of selecting the material on each component to match the function.

We have steel sides and arms on our robot, but the pneumatic catapult hoop is PVC. The flex actually adds to the strength of the shot.
The Catapult is supported by fiberglass strut-channels on the power-end and aluminum squares with pine inside them to prevent crush on the hold-down end.
We have numerous guards that are polycarbonate
the 'floor' of our frame is 3/8" UHMW so electronic components can be just screwed down with wood screws.
So we've used just about every material on our robot somewhere.

Just like in any engineering, I believe material selection is a process and needs to be thought out for each part. I teach the kids a class on it too.

[Steven Smith]

As many others have said, build using what you have experience working with and tools capable of producing with.

In 2014, my first build season with the team, we had a "basic" shop with drill press, chop saw, small manual mill, etc. Most everything was COTS and we used a lot of VersaFrame product.

Since 2015, we rely on our in house CNC router for large flat parts. In 2015, we used a lot of aluminum tube profiles (1x1-3x2 OD, walls of 0.0625 to 0.125 and everything in between), with custom made flat pieces like gussets, larger panels, etc. Our elevator carriage still used a bit of VersaFrame. Our drivetrain was manually milled tubes for chain in tube.

In 2016, we acquired a manual brake (thanks 2848!) which let us make more complex geometries using our router and more precise sheet metal bends. Our robot is one of the more robust out there, and we are nearly 100% rivet construction. We learned the lesson of moving to 5052 for bending. We also saw a lot of good examples of polycarb usage for mechanisms that bend instead of break, most notably (to us), 1477s intake in 2014, which inspired a lot of polycarb usage on our robot as ball guides, intake mechanisms, shields, etc.

Next year, we plan to use many of the same materials and techniques, and add better jigging to do aluminum tube extrusion bearing holes and lightening patterns on our CNC mill, as well as gearbox designs. The existing gearboxes are all probably better quality than what we can make, but some years the packaging flexibility of making something slightly different would be nice.

Outside of all that, we use a laser cutter to make Delrin spacers in house for cost savings and use 3D printing extensively (ABS/polycarb).

[mwmac]

Team Tators built this year's robot using aluminum with the greatest variation in thicknesses I have ever seen on a robot. All sheet stock is .08" for the chassis while the front plates were milled from 1.5" thick plate, (finished at 1.46") . Yes, they are pocketed....

[garyklein]

6061 robotextrusions and 5052 aluminum plate.

The extrusions are fastened with 10-32 socket head cap screws.

There are a couple drilling jigs available to locate and guide the drills and taps needed.

[ThaddeusMaximus]

Originally Posted by Poseidon5817

We're pretty close to the same as you guys, main sponsor works in stainless sheet metal, so we do too. I think we used entirely 18 gauge, except for our shooter wheel mounts.

I pity your souls, having machined some stainless last year... although if you jet most everything, not as big of a deal.

[JPBlacksmiths]

We usually use one inch C-Channel aluminum for our chassis and for the rest of the robot we usually use one inch extruded aluminum and one inch aluminum square tubing. We occasionally use steel when more strength is needed, but we prefer aluminum for the price and weight.

Some people brought up welding as the best option for robot assembly, but we don't do that due to our limited budget. By bolting the majority of our metals together, we can take the robot apart and re-use some of the metal for the next year.

[arc25565]

Our team typically makes most of our robot out of 1"x1" and 1"x2" square aluminum tubing. We also use lots of 90 degree 1"x1" angle and 1" by 1/8" bar. Everything is 1/8" thick. I find that if you go much thinner than it is really easy to over tighten things.

[Mr. Ackroyd]

Last year our team went with 5052 1/8" sheet aluminum and 1"x 1" x 1/16" aluminum tubing. We also used churro bar for standoffs and turned down aluminum round stock. Our team has always incorporated aluminum welding as we have had mentors in the past train students. however, this year we had a specialist from the Navy come in and really train the kids as we had some tricky areas. We are lucky enough to have mills and lathes to take down our parts when needed.

Last year we had a local college (RPI) water jet our plates and that helped out tremendously. This year we picked up a CNC plasma cutter and plan to cut all plates with that machine. So we will be building our entire robot in house.. We also plan on making parts for local teams when needed.

[Anna F15H]

We use an aluminum extrusion called Item. We typically make our frames out of the 20 mm x 20 mm and 20 mm x 40 mm options. It is very convenient for making quick adjustments with T-nuts without drilling lots of new holes every time we want to move something. I've never experienced any issues with it bending or losing its structure.

[Mike Schreiber]

Originally Posted by dmorewood

6061 should never be used in a bent piece. The metal has a interesting habit of cracking and "exploding" when bent in a break.

Our frame was 0.060" 6061 last year. You can bend it fine. Until 2016 we've generally used 5052, but it's certainly doable with 6061. I'm not sure what temper we get, that might make a difference.