Tube Versus Channel

[Gray Adams]

Originally Posted by MICHAELABICK

We also like aluminum tube. Really, the best thing to use is 1 x 2 aluminum tube, welded. 1/8 in thick for drive base, and basically 1/16 for everything else. If used correctly it is perfect. Minimize the amount of frame material you need. Look at any 254 robot, and you will see how simple the frame actually is. It makes for lighter robots, and you really don't need anything more. Also, 1/4 in, waterjetted, aluminum plate goes very nicely with this. It makes building 20 times easier, and reduces the amount of tubing you need. Plus, you can make custom gearboxes.

2 questions.

1) Is your 1/4" plate .25", or is it like ours and ranges from .22" to .24"? That made our gearboxes this year a little difficult to get fitting correctly (if you've seen the gearboxes, you know what I mean)
2) Besides custom gearboxes, how else do you use it in your frame? We have a lot more frame right now than I'd like, but I can't see how 1/4" plate would make it significantly better.

[FrankJ]

If your 1/4 plate is .22 to .24, you ordered a gauge thickness rather than 1/4 plate.

1/8x1 tube is virtually the same weight as 1" 80/20.

This year we used a lot of 1/8x1 angle. Half the weight of the equivalent channel & allows bolts to be properly torqued without crushing the section.

We use mostly 1/4-20 bolts. A little heavier than other options, but you don't have to worry about the inexperienced over torquing them. Carroll Smith has a great book about fasteners "Nuts, Bolts, Fasteners and Plumbing Handbook"

It is all about the details & trade offs.

[MichaelBick]

Originally Posted by Gray Adams

2 questions.

1) Is your 1/4" plate .25", or is it like ours and ranges from .22" to .24"? That made our gearboxes this year a little difficult to get fitting correctly (if you've seen the gearboxes, you know what I mean)
2) Besides custom gearboxes, how else do you use it in your frame? We have a lot more frame right now than I'd like, but I can't see how 1/4" plate would make it significantly better.

Our 1/4 plate is .250 ± .001. We got it from McMaster, because we actually had to get it CNC milled by our machine shop. We hadn't tried to get a 2D sponsor before the season, but actually right after the end of build season, we got industrial Metal Supply to sponsor us, and they have a laser cutter that we will be able to use for the offseason and any future games. This is just one of the laser cutters that they have available: http://www.youtube.com/watch?v=-k8JGL8Muq4

We use the 1/4 plate for our ground pickup, shooter hood, and elevator gearbox, which we also made custom. This helped to simplify our frame quite a bit. What I was really talking about though, is it seemed like a lot of teams have way more complicated frames than needed. I like using 1/4 plate, wherever it seems like it would be beneficial to use sheet metal, as it has a lot of similar capabilities, and it adapts to whatever you need it for very well.

[Madison]

Most of our machines are made from 1x1x.063 aluminum tube and 1/8" polycarbonate gussets that are fastened together with 1/4" rivets.

1/4" rivets are definitely overkill, but they make prototyping with 1/4" hardware and swapping in rivets at final assembly a cinch and our laser cutter doesn't always do such a great job when cutting smaller holes into some thicker parts -- a #10 clearance hole in 1/2" material gets pretty oblong by the end.

This year's drive pods were built from aluminum standoffs and 1/4" delrin plate; I was a bit worried about how well the plastic would handle side-loading, but it's been a champ so far.

With respect to tube vs. channel -- in almost all cases, I'd use tube if I could. Tube is much stiffer than channel in torsion.

[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.

[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!

[George C]

We used 3 x 4 x 1/8 rectangular aluminum tube for side rails with wheels and chain runs mostly inside the tube. It wasn't easy to find but Metals Depot (metalsdepot.com) stock it and ship to Canada with no problem. By the time we finished with the tube there wasn't a whole lot left so it was light and very strong. Cross members were 1 x 2 x 1/8 rectangular tube with loads of lightening holes. The chassis is tig welded. 1 x 1 x .090 square tube was used for the superstructure. Here's a photo.

http://www.othsrobotics.ca/images/isabella.jpg

Rivnuts are great but do strip out easily if installed by the inexperienced. They also don't allow for two pieces to be tight together as there's a flange on the nut. Rivnut kits are available from Princess Auto for about $35 (http://www.princessauto.com/pal/prod...ting-Tool-Kit). That gives you the tool and then you can buy more rivets from McMaster Carr. Unfortunately the kit doesn't include 10-32. Making a 10-32 mandrel was straightforward once we bought a 10-32 LH die and much cheaper than buying a kit from McMaster Carr.

[Kevin Sevcik]

Originally Posted by Siri

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

It IS that much faster cutting aluminum extrusions. I'd used it on solid aluminum, and it's probably about equal on the cutting speed. But even then, you're saving time on post-processing. The circular saw leaves a cut that's much flatter and smoother, with deburring only necessary to remove the occasional thin burr and round off those sharp cut edges. Even past the processing speed, though, is the fact that it's a compound miter saw. If you maintain it and keep your fences square and in-line, you can pretty accurately cut whatever angle you want.

It's also a lot easier to get cuts to the exact length you want on this saw. Cut your part 1/16" longer and measure it. If it's right, stop. Otherwise, with the saw blade down and off, slide the piece over till it touches the flank of the blade. Hold your part, pull the blade up, turn it on and run it down and you've just taken off the tiny distance between the the flank of the saw blade and the outside of the kerf. It's something like 1/32" or less, so with a little extra effort, your nice square cut tube will be within 1/32" of where you want it.

The only downside is that a standard woodworking miter saw will only be good for cutting aluminum and your kerf is definitely larger than on a bandsaw. But it's still only 0.094", so unless you're cutting a heck of a lot of 0.5" pieces or something, you're not going to notice or care.

[Bill_B]

I was thinking of the pre-cuts as basis for prototyping frames of superstructure. We use a primarily wood-shop, so prototypes tend to get made of scrap lumber. Cutting and fastening them together securely seems to suffer for the focus on getting right to trying the mechanism. If a reasonably secure framework can be made quickly, then maybe the ideas won't get lost because the prototype was too flimsy to tell if the idea were any good.

Sorry, that seems cloudy even to me. Just think making a sloppy pile of crates to get to the cookie jar. More attention to solidity means better validation of the demonstrated principle.

[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.