Tube Versus Channel

[Siri]

Originally Posted by Kevin Sevcik

Lacking the fabrication support necessary for the above, 57 has settled on the kit frame with a chassis of 1"x1"x1/16" wall square aluminum tube, mostly held together with more 1/16" sheet plates riveted with 3/16" aluminum structural rivets. It's pretty lightweight, plenty strong if you're not dropping your robot off a cliff, and we can get 20' sticks of the stuff for $6 from a local supplier, even on a Saturday. Which is harder to say about AM channel or 80/20 or another T-slot extruded aluminum.

Do you have any advice or books/white papers/etc to recommend concerning designing for 1/16" tube? We're pretty much all 1/8" tube or angle for everything on our bots. I've heard great things about 1/16", but we've warped welded 1/8" chassis occasionally so there's some hesitancy.

Price:
From what I've found it's really very, very location-based. We used to buy everything from McMaster until we discovered the joy of local surplus stores. If you think you might be missing something, introduce yourself to a local machining company or two (or ten). They'll know. Different profiles definitely offer a lot more design flexibility. Certainly I'd think 1/8" C-channel on the tower is over-designed. Maybe angle if you want to stay with 1/8".

[MrForbes]

Originally Posted by Siri

Do you have any advice or books/white papers/etc to recommend concerning designing for 1/16" tube? We're pretty much all 1/8" tube or angle for everything on our bots. I've heard great things about 1/16", but we've warped welded 1/8" chassis occasionally so there's some hesitancy.

The chassis could use 1/8", but on stuff that doesn't need to be that thick, like the upper structure, 1/16" is usually fine. But it depends on how you design it! We like making upper stuff from 1/16" tube and riveting 1/16" sheet or angle brackets to hold it together, and attach stuff to it.

It's all in the design....

[Chris Fultz]

We use almost all 1"x1" square tube. In some places we use 1"x2", but very little of it.

If you look at our 2012 robot, the lower level of the frame is 1/8" wall, mainly because we have our drive wheel bolts mounted through it. The front and rear pieces where the shooter mounts are 1/8" wall. All of the rest is 1/16".

The robot frame is almost all welded by students. They practice a lot in the fall with welding scraps of the 1/16" wall to get good at it. It is easy to burn through.

[Billfred]

Originally Posted by Kevin Sevcik

I think your hands down favorite/best material to construct a robot out of is waterjetted and bent aluminum sheet metal, since you can design it to the exact requirements you need, given you an optimum strength to weight ratio.

Lacking the fabrication support necessary for the above, 57 has settled on the kit frame with a chassis of 1"x1"x1/16" wall square aluminum tube, mostly held together with more 1/16" sheet plates riveted with 3/16" aluminum structural rivets. It's pretty lightweight, plenty strong if you're not dropping your robot off a cliff, and we can get 20' sticks of the stuff for $6 from a local supplier, even on a Saturday. Which is harder to say about AM channel or 80/20 or another T-slot extruded aluminum.

Thick wall AM style channel is heavier and tougher than we need for any framing purposes. Thin wall channel would be flimsier than tube, if lighter. Either of the u-channel options means you have an entire side that can be a pain to attach things to.

80/20 style extruded aluminum is good for prototyping and quickly adjusting parts, etc. Only problem is that it's heavier than the 1/16" wall tubing that we use, for no more benefit than the quick propotyping.

I was about to write about 2815's construction methods of recent years, but this really is what we use--the last two robots (with three blue banners between them) have been constructed of 1"x1" square tubing acquired from the Lowe's near where I work (which is not as cheap as Kevin's aluminum--I want your source!), attached with gussets of various sizes and shapes (we use some angle as well) with rivets and attached to the AndyMark C-Base kit frame. For all the nail-biter moments these two robots have given us, the structure has been rock solid.

It's been many years since I worked with 80/20 (and then as part of an elevator rather than a frame); the stuff can definitely get heavy. If I were building a sliding mechanism, or a part that I knew would require a lot of quick adjustments, I would consider it...but I doubt I'd want to build a whole robot out of it.

Originally Posted by Siri

Do you have any advice or books/white papers/etc to recommend concerning designing for 1/16" tube? We're pretty much all 1/8" tube or angle for everything on our bots. I've heard great things about 1/16", but we've warped welded 1/8" chassis occasionally so there's some hesitancy.

We build our structures so the 1/16" tubing is inboard--the only exception was our original roller claw in 2011 (which broke when our drivers smacked it into the player station glass at speed). From there, it's just been judicious application of 1/8" rivets (sometimes by overzealous freshmen) to hold it together. If you get to St. Louis, look us up--there's no secret sauce to our framing setup, and we'd be happy to show it.

We haven't tried welding any of our parts--call it a bit of paranoia about breaking parts in the heat of competition. Granted, we could duct tape it these days...but the idea of just throwing rivets into a new piece of metal has its appeal.

[FrankJ]

Where to buy? 80/20 has other shapes. Price is better than local hardware store. Most places have metal supply companies where you will get the best price. They typically have large minimums so you need to buy in bulk. If you explain what are doing they will often waive the minimum charge, but you will still need to buy all you need at once.

[Kevin Sevcik]

Originally Posted by Billfred

I was about to write about 2815's construction methods of recent years, but this really is what we use--the last two robots (with three blue banners between them) have been constructed of 1"x1" square tubing acquired from the Lowe's near where I work (which is not as cheap as Kevin's aluminum--I want your source!), attached with gussets of various sizes and shapes (we use some angle as well) with rivets and attached to the AndyMark C-Base kit frame.

Erm. Well I seem to have underestimated that price slightly. I'm told the 20' lengths were around $20. I'm obviously only nominally in charge of the robot's budget, heh. Our local source is SSS-Steel. You mileage may vary with a local ferrous/non-ferrous supplier. I'll admit the Port of Houston gives us a bit of an advantage on raw material prices like this. Still, if you can find yourself an actual bulk metal supplier that's local to you, you're probably going to get better prices (and better material) than you will at Lowe's. Just do a google map search for "aluminum" or "non-ferrous metal" near you. For instance, Billfred might give a call to Loxcreen or Charleston Aluminum (who apparently has 2024 1" x .062" sq tube in stock. I'm envious.). If they won't sell in small lots to you or only sell to businesses, they might still be able to point you to a local distributor that can help you. Just think twice about buying from Metal Supermarkets. They specialize in selling small cut lengths to whoever, and they have a markup to prove it.

At any rate, comparing costs of my 1/16 wall tube to an AM C-Channel, you're talking $20 to $18+shipping. But you're getting 20' of tube to 3' of channel. And I can get more tube on a single day notice. So yeah, I think there's significant advantages there.

In other news, while we're getting pretty good at the 1/16 tube and plates and 3/16 rivets construction, I'm always looking to simplify things. Especially if it means I don't have to shear and break a bunch of corner brackets at work in my copious free time. So has anyone looked at or tried these tubing connectors yet? I swear I saw a team using something like this for their tube based frame, so I started hunting. They look a bit heavier than the plates we're using, but I think things would come out straighter and less complicated. And you could assemble your frame and test things before you put a screw or rivet into the connector to secure it.

[MrForbes]

Originally Posted by Kevin Sevcik

In other news, while we're getting pretty good at the 1/16 tube and plates and 3/16 rivets construction,

wow, those are big rivets. We usually use 1/8 or 5/32" rivets on thin aluminum. We save the big ones for heavy stuff.

[Kevin Sevcik]

Originally Posted by squirrel

wow, those are big rivets. We usually use 1/8 or 5/32" rivets on thin aluminum. We save the big ones for heavy stuff.

We use aluminum interlock structural rivets. They only go down to 3/16". They're probably overkill, but they have good clamp-up and hole filling. And Allen Gregory from 3847 pointed out that they use the same drill as a #10-24 clearance hole.... So if you standardize on 3/16 rivets and #10-24 screws, you only need one drill bit for a lot of your construction. 3847 is doing that, and it sounds like a nifty idea to me.

[IndySam]

We love the 3/16 rivets and have also started standardizing on 10/32 after doing 1/4-20 for years.

We also use hysol for the gussets we don't plan on removing.

Our robots are also mostly constructed from 1x1 tube in both 1/16 and 1/8 thicknesses.

1/8 c-channel is also a great choice for many parts.

I love prototyping with 8020 but we rarely use it for anything other than pneumatic supports that need adjustments.

[Bill_B]

Originally Posted by Kevin Sevcik

Especially if it means I don't have to shear and break a bunch of corner brackets at work in my copious free time. So has anyone looked at or tried these tubing connectors yet? I swear I saw a team using something like this for their tube based frame, so I started hunting. They look a bit heavier than the plates we're using, but I think things would come out straighter and less complicated. And you could assemble your frame and test things before you put a screw or rivet into the connector to secure it.

Jumped over to their site. I admit the connectors look good for quick assembly, perhaps rivaling 80/20 in quickness, if you have a bunch of pre-cut "standard" length tubes. building a frame would be quick and you could set your tube pieces up to give useful outside dimensions for the assemblies.

No dimensions given for the connectors - but I infer from the tubing they're selling that there might be a problem with 1/16 1" tube. They list wall thickness for their tube as .065", so the connectors must fit inside there, snugly? Their other option has walls .060 and listed as "slip fit" for things you want to disassemble easily. This makes one wonder how the connectors will fare in the .0625" walls we're thinking about here. Loose-ish but not slippery? I guess I'd have to buy a few for a sample frame to get some hands-on trials.

Esto has quite a few tube profiles with flanges and such. Most are anodized since their target is the construction of static displays and machine guarding frames. They are also rounded edges for a more friendly handling feel.

[Kevin Sevcik]

Originally Posted by Bill_B

I admit the connectors look good for quick assembly, perhaps rivaling 80/20 in quickness, if you have a bunch of pre-cut "standard" length tubes. building a frame would be quick and you could set your tube pieces up to give useful outside dimensions for the assemblies.

No dimensions given for the connectors - but I infer from the tubing they're selling that there might be a problem with 1/16 1" tube. They list wall thickness for their tube as .065", so the connectors must fit inside there, snugly? Their other option has walls .060 and listed as "slip fit" for things you want to disassemble easily. This makes one wonder how the connectors will fare in the .0625" walls we're thinking about here. Loose-ish but not slippery? I guess I'd have to buy a few for a sample frame to get some hands-on trials.

Precut standard length tubes? I should introduce you to my new best friend, the Diablo Non-Ferrous Circular Saw Blade. Toss this into your favorite 10" miter/chopsaw and you'll be amazed how fast you can put out tube for frames. I CADed the frame for our shooter, wrote out a cut list, and we had all the tube parts cut and ready to go in less than an hour. With accurate bevels and clean square edges. I can't tell you how happy I am the I noticed it on a Lowe's trip a few years ago. It makes it easier to work with just about any long aluminum on the bot. In fact, I think it's so nifty, I'm doing this:

Teams, if you do any significant manual work with long aluminum tube, channel, the kitframe, pretty much anything aluminum, then you need to buy this Diablo Non-Ferrous Circular Saw Blade and a half-decent chop saw like this Hitachi 10" Compound Miter Saw. You will be amazed how much faster and better things go vs. your current vertical/horizontal bandsaw, hacksaw, or dull butter knife. You'll wonder how you ever managed without it.

Ahem. And now that that's out of my system... Yes, I'm a little concerned about the fit of those connectors in various aluminum square tubing. I think I'll be lucky enough to have it work for me, and my terribly cheap square tubing from SSS-Steel just so happens to be nominally 0.065" wall. So I should be fine, but others mileage may vary.

Also, 8020 actually has a similar line of tubing and connectors marketed as their Quick Frame series. No clue if it's better or worse, but it looks like it mates up pretty easy with the standard 8020 profiles for teams that want to mix and match.

[smclean1969]

If you have a local aluminum supplier, just tell them that you'd like to purchase any 1"x2"x1/8" or 1/16" wall aluminum that they have as scrap. You can cut your costs from about $3.25 per foot to $.40 per foot. Work it year round and you'll have plenty of material come build season.

[Hawiian Cadder]

We used 3*1.5 inch tubing with .125 thick walls and a special hole pattern cut into it this year. 3/16 rivets and grade A 10-32 Button-heads are our fasteners of choice. This year the drive frame weighed 10lbs, and the entire frame weighed less than 16lbs. If you have the machining resources to do it, I would look at perforated tubes as a construction method, I cannot think of a way to make a lighter frame. For some examples check out team 40 or 111's robot from 2011

[Siri]

Originally Posted by squirrel

It's all in the design....

Of course, that's the part we're trying to figure out! We'll keep at it. And (Billfred) if we make it to Worlds we'll definitely look up 2815. Thank you.


Is the circular saw blade really that much faster than a horizontal? That's impressive. I may make the investment.

[pfreivald]

Originally Posted by Siri

Is the circular saw blade really that much faster than a horizontal? That's impressive. I may make the investment.

Yes. Worth every single penny!