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

[z_beeblebrox]

1/4" baltic birch plywood is most of our metal, whether for structures or gussets. It's exceptionally strong, lightweight, easy-to-machine (even without a laser cutter) and inexpensive. We also use some 1/8" plywood for small or non-structural stuff.

In terms of actual metal, we mostly use 1x1x1/16" square 6061 tube. Its profile gives good resistance to bending and twisting and its thin wall keeps weight low. Also, lots of Vex 1/2" tube axle (with the ends tapped for 5/16-18 bolts) for both axles and standoffs.

We also have some small parts that take high loads (axle mounts, winch ratchet and pulleys) laser cut from .125" 5052 aluminum by a sheet metal shop that sponsors us.

We'll also make small parts out of HDPE or Delrin on our CNC router or from thin delrin sheet on our laser cutter. Lexan sheets are also occasionally used.

We occasionally use 1x1x1/8" or 2x2x1/8" 6061 angle and 1/8" or 1/16" 5052 sheet if it better suits the application.

For fasteners we use #8 Torx screws for wood-wood joints, 3/16" rivets where possible in metal (lighter, easier to work with than bolts), 10-32 and 1/4-20 bolts where rivets won't fit or aren't strong enough and 5/16-18 bolts for attaching tube axle. Mostly socket-head cap screws from McMaster-Carr with nylock nuts.

Edit: glad to see a good mechanical design discussion thread going. I've been missing these.

[bobl]

Metal? What's that?

[dmorewood]

In your original post you have the basic flat sheet aluminum. But if you go down that road you also need to understand the different types and how to use it. First off you need to have a dedicated CAD designer that understands how to design with sheet metal and the appropriate way to bend and rivet Aluminum. Also the two most common types of aluminum for FRC, and what I recommend for your first year designing with it, is 5052 and 6061.

5052 should be used in flanged(bent) pieces. Technically you can use it for just flat pieces to, but it's not as strong as 6061.

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

Oh and by the way you will also need to find a company that can cut and bend your aluminum design for you. Depending where your team is located I may be able to help you with that.

[Max Boord]

1065 uses .125 thick C and L channel as well as versa tubing for our robot construction. We buy large amounts of it before the season starts and get it powder coated early in the build season so the end robot is always powder coated without taking time out of the build season to get it done.

4592 is an all sheet metal team. So the entire robot is built from .090 5052 made by our sheet metal sponsors. Occasionally .125 inch is used when thinner material is not strong enough. We also use quarter inch thick plate for gearboxes and wheel hubs.

[mman1506]

Originally Posted by hrench

I remember aluminum robots put together with rivets--they were always rickety and wobble. These are solid.

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

[Chief Hedgehog]

Originally Posted by bigbeezy

Vast majority is 1x1 and 1x2 Versatubing. We do have some 3/4x3/4x1/16 tube this year.

For plate we mostly use 0.090" 6061, with the occasional 0.040" for light brackets as we can bend it in house. We do have 1/4", 1/2" and even 1" thick AL on the bot this year.

Most hex shafts are AL from VEX, though we do use some steel hex from McMaster. We tried the Thunderhex and I'm not sure if it was just the oversized batch but it was a nightmare to work with and we won't be going back.

We rivet most everything and get critical pieces welded by our local sponsors.

I concur on the Thunderhex. What a horrible product - we had one student that spent about 2 days just filing down the Thunderhex so that we could use it. We will be looking at other stuff for next year.

[z_beeblebrox]

Originally Posted by Chief Hedgehog

I concur on the Thunderhex. What a horrible product - we had one student that spent about 2 days just filing down the Thunderhex so that we could use it. We will be looking at other stuff for next year.

We've had success with chucking the ThunderHex in a lathe and sanding it with emery cloth. We can do a 36" piece in a few minutes.

It would be awesome if the tolerances were fixed for next season though...

[ratdude747]

Originally Posted by hrench

We have a flux-core wire-feed welder in the shop, which is inexpensive to operate and the kids learn to make some great looking welds. Add a bracket? don't need to drill and bolt--just weld it on! Also note, we've never had the money for aluminum welding.

Have you ever considered MIG or TIG as an upgrade down the road? Flux core welding has at least in my experience been a bit sloppier due to the slag. MIG is just as easy and produces better welds when welding indoors. TIG, while often considered an "aluminum" process, is also great for steel and allows for cheaper TIG equipment (AC is required for aluminum and adds quite a bit of cost). Sure, the gases add cost, but the resulting welds are better looking (no slag to chip) and possibly stronger (although that's more a factor of the welder's skill).

[asid61]

Originally Posted by mman1506

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

Forget 1114, look at 148!
All of that aside, we use:
2x1 aluminum tube, 1/8" and 1/16" wall. We use the 1/8" wherever there are bearings in the tube, and 1/16" when we don't need the strength or aren't worried about crushing.
1x1 aluminum tube, 1/8" and 1/16" wall. 1/8" wall is more common for the strength. 1/16" wall is rather rare but comes in handy for small stuff (like our can stabilizer last year or climber hook depositer this year).
1/8" aluminum plate, for most gussets (although this year we used 3/32 with a hole pattern to emulate a versagusset).
1/4" aluminum plate, for bearing plates and especially for when we used tapped plates. Beats using a nut and wrench in a tight space any day. Plus, it works great for screwing thing tubes together.

1/2" hex shaft for nearly everything. 7075 from Vex. We got a run of too-tight thunderhex, but apart from that I think it's great stuff.

[pipsqueaker]

Originally Posted by Chief Hedgehog

I concur on the Thunderhex. What a horrible product - we had one student that spent about 2 days just filing down the Thunderhex so that we could use it. We will be looking at other stuff for next year.

It's worth noting that ThunderHex is actually supposed to fit really tight, as theoretically it eliminates the need for collars and can fricton-fit through holes meant for round shaft. We use a ton of it on our robot and we never needed to sand it down to fit.

However, looking at the webpage I do see their notice that their current inventory is oversized due to a manufacturer error, and I do see how working with that could be a bit of a nightmare

[Captain_Kirch]

Originally Posted by hrench

We use steel.
...
Takes up less room too. Can't imagine building in 1/2" tubes in aluminum. Would fold like tinkertoys. Steel is super strong.
...
Yes, steel is heavier, but we just use less.

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

We have had quite a bit of sucess with welded aluminum extrusions. We build robustly, and even in the toughest years for robot impacts (2014) we still have a robot to show for it. I think most of us remember how bad the hits got in 2014, but Jeffrey survived two regionals, Archimedes division, Einsteins, IRI, R2OC and Robofest. We're playing defense against our practice bot this year with that robot. Aluminum holds up if you have enough of it.

I don't think I've seen steel robots in this area though, its definitely unique.

[Boltman]

We uses a lot of 80/20 aluminum to build this year and last...supplemented by Steel for bracing/shafts. Plus Polycarbonate and whatever comes in KOP. Spring steel here and there. Came in at a healthy 107 lbs usually we are at 120lbs. We used wood also for winch box.

[GeeTwo]

As for aluminum grades, we pretty much follow the usual ways things are manufactured, and a bit of research after the fact showed this to be right in the vast majority of cases.

That is, you will notice that 6061, 6063, and 7075 are generally extruded and then tempered. Don't plan to put a sharp radius bend into any of these unless you're going to retemper. (and we don't have the faciilties).

5052 starts off stronger than any of the grades listed above, but does not add much strength in tempering. This is the material of the recent KoP chassis, Vex gussets, and Vex VF angle and c-channel. If we're going to bend some plate, this is our #1 choice. Even with 5052, be sure that you are bending around a radius about twice the thickness of the plate, and bend ONCE. Metal fatigue is another of the one hundred seventy three ways for a team to ill its own robot.

[katabolt]

Here at 3674 we build our bots with old-school AndyMark C-Channel. Sure it's heavy, but dang is it robust.

[Michael Hill]

This year, we used a lot of 1" x 2" 6061-T6 aluminum rectangle tube in both 0.125" and 0.063" wall. We also used a good amount of 1" x 1" x 0.125" 6061-T6 aluminum square tube. Our sheet metal belly pan was 0.063 6061-T6 aluminum and the impact "plates" were 0.063 2024-T3 aluminum sheets (stronger aluminum for where we could have potential impacts. We used self-adhering UHMW strips along the bottom of our robot to help us slide over the rock wall. Our drive shafts went from ThunderHex to just regular 0.5" hex 7075-T7351 aluminum shaft. We use a healthy amount of 0.25 6061-T6 aluminum plate for gearboxes, shooter rails, shooter, and pillow blocks. Our pickup mechanism plates were the same 0.25 plate. Our rollers were latex surgical tubing slipped on aluminum tube with a poor man's hex end caps (We lathed down some Vex 0.5" hex gears and pressed them in the ends of the aluminum tubes). We've got some polycord in our intake system as well.

Our hardware consists of mostly rivets, but there is a healthy amount of #10 and 1/4-20 hardware on there. We'll use mostly aluminum rivets, but there are some steel ones on there as well (for extra strength in a smaller size).