Building the Structure of the Robot?

[ksafin]

Hello all.

I believe many beginner teams (including us) use aluminum extrusion such as 80/20 or T-Slots, as it's very simple to use, intuitive, and cost effective.

However, as we progress throughout our FIRST life, we're seeing more and more cons to extrusion.

Extrusion is considerably heavy in comparison to alternatives such as custom machined lightweight aluminum.

It's also not nearly as flexible for construction, given it's only a straight 1"x1" rod really.

My question to you all is, how would you suggest/think (or if you've personally started by using 80/20) wane off the use of extrusion and transition onto more advanced structural materials?

To add to that, in what way can you accomplish this given low-moderate funding ($7,000/season), and pretty much no specialty tools (unless the tool in question is affordable). I'm saying we only have a Miter Saw, Drill Press, and Bench Grinder. Scroll Saw & Band Saw are not out of the question.

Thanks!

[Billfred]

2815's past two robots have largely been made of 1" square tubing (1/16" wall) and flat and angle to gusset it. If you don't have the resources for a full-on sheetmetal design, this is hard to top.

[IKE]

Originally Posted by Billfred

2815's past two robots have largely been made of 1" square tubing (1/16" wall) and flat and angle to gusset it. If you don't have the resources for a full-on sheetmetal design, this is hard to top.

I couldn't agree more with Billfred on this one. The switch over to 1/16th wall box will reduce costs and weight as long as you spend some time designing your layout out instead of relying on sliding parts.

This should be an easy switch as it is still 1x1 construction. Some friends on 3302 will pre-drill their square tubing with holes on the center line every 1" (or maybe 3/4 or 1/2"). The small holes allow the box material to be easy construction similar to the "kit" extrusions. this allows allows for some kids that are not interested in design to start making stuff right away while the others design to this constraint. this is a neat option, but you do loose some flexibility of dimension. 1x1 is also really common and in a pinch can be found at most Home Depots.

If weight is a higher priority, switching to round tubing for upper structures is a great weight savings, but significantly harder to work with. Round versus square is a 25% savings for the same wall thickness. Round also has lots more wall thicknesses and material compounds to choose from. This too can add to weight savings. Make sure you get some good pictures of how 469 builds their robots. They are (IMO) masters of the thin wall no weld construction.

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All this being said, 3 of my favorite and most competitive robots last year used 80/20 or star bar (25, 341, and 1023). These 3 were able to do it all. They were good shooters, good at collecting, and able to do the bridge well.

[Billfred]

Originally Posted by IKE

I couldn't agree more with Billfred on this one. The switch over to 1/16th wall box will reduce costs and weight as long as you spend some time designing your layout out instead of relying on sliding parts.

Or you do what we did: craft the shooter on the fly, realize you had some parts wrong, drill out the rivets, place them in the right place, re-rivet...

...and then putty over the holes before painting.

[ksafin]

So..

Our time doesn't really want to weld, nor do we want to allocate resources to buy a good welder.

As far as gussets go, where would we get them/how would we make them? Is it just any shape plate with bolts..?

[Billfred]

Originally Posted by ksafin

As far as gussets go, where would we get them/how would we make them? Is it just any shape plate with bolts..?

2815's gussets have been 1/16" flat and angle aluminum from the hardware section of Lowe's, riveted using 1/8" aluminum rivets (usually 2-4 on each end). Cheap, easy to install, easy to repair.

I'd love to see us get to a bent sheetmetal gusset like some of the ones shared here...but the results are suitable for competition.

[MichaelBick]

Originally Posted by ksafin

So..

Our time doesn't really want to weld, nor do we want to allocate resources to buy a good welder.

As far as gussets go, where would we get them/how would we make them? Is it just any shape plate with bolts..?

The best way imo is to make them in house with a cnc router or with a sponsor who has a waterjet. Either way it will be very little time investmet. Just make sure to make the gussets as thin as possible(1/16 is likely fine fo many applications). By making the gussets thinner you don't have to lighten them. In addition because you don't have to run a lightening pattern and because the parts are thinner they can be machined extremely quickly.

[ksafin]

Originally Posted by MICHAELABICK

The best way imo is to make them in house with a cnc router or with a sponsor who has a waterjet. Either way it will be very little time investmet. Just make sure to make the gussets as thin as possible(1/16 is likely fine fo many applications). By making the gussets thinner you don't have to lighten them. In addition because you don't have to run a lightening pattern and because the parts are thinner they can be machined extremely quickly.

Uh, we have access to neither of those.

[Tom Line]

Cutting triangles out of square pieces is very easy with a bandsaw. That's how we made all the gussets for our after-season stinger addition. It also has a huge benefit: it's fast and you don't have to wait for anyone. If you want to match drill them - make all your gussets in advance, clamp them together, then drill through them in one shot with a drill press. Your gussets may not be be exactly the same, but the hole pattern will be.

[Billfred]

Originally Posted by ksafin

Uh, we have access to neither of those.

Do you have access to a hacksaw, metal file, and a drill?

Congratulations, you now have all the tools to make gussets the way 2815 does.

There's not a lot of magic to it; if you're worried, get a stick of 1" square tubing and a short (say, 2') length of 1/16"-wall, 1" angle aluminum. Make a box out of the tubing, riveting it with the angle used as gussets. Kick it around the shop a bit and observe its properties in the context of what a robot would encounter (usually with bumpers, remember). You'll be pleased, most likely.

[MrForbes]

Drill all the rivet holes in the gusset, then clamp the gusset to the bigger parts. Then drill the first hole all the way thru, and pop a rivet in it. Continue drilling and riveting one hole at a time, until there are two rivets in all the parts. then you can drill all the rest of the holes, and put in the rest of the rivets.

We've been doing this for building our "structures" for years....it's time consuming, but cheap and easy and doesn't take much equipment.

[ksafin]

Thanks for the quick replies guys, I'll forward all of this to our Mechanical Captain.

While I'm one of the more mechanically savvy guys on the team, the final call is to the captain

Also, another question/concern. With 80/20, we had the flexibility of just putting a drivetrain together with the parts, and then when we needed to change something or add something, it was a matter off adding a connector or taking this off or adding this. Very simple, with little modification.

I imagine that by using aluminum sq tubing w/ gussets and all, we'll have to plan our drivetrain out much more thoroughly than we did with 80/20 (unless we plan to have a lot of random holes from taking gussets off and on xD)

Is this correct, and how do you cope w/ this?

[Billfred]

Originally Posted by ksafin

Thanks for the quick replies guys, I'll forward all of this to our Mechanical Captain.

While I'm one of the more mechanically savvy guys on the team, the final call is to the captain

Also, another question/concern. With 80/20, we had the flexibility of just putting a drivetrain together with the parts, and then when we needed to change something or add something, it was a matter off adding a connector or taking this off or adding this. Very simple, with little modification.

I imagine that by using aluminum sq tubing w/ gussets and all, we'll have to plan our drivetrain out much more thoroughly than we did with 80/20 (unless we plan to have a lot of random holes from taking gussets off and on xD)

Is this correct, and how do you cope w/ this?

We've been known to add a few extra holes to our robot through bad planning. In 2011, we even took a piece of our arm structure, rotated it around, and drilled a new hole for lack of another piece.

It all comes down to what kinds of forces your pieces will see and how picky you are about appearance. When we botched parts on this year's robot, we took the metal that was still usable in-place and redrilled new holes and placed putty into the holes left behind to smooth it out. Metal that was too weakened from the holes for our liking was cut down and reused in other places when possible. Very few pieces were junked entirely.

But, of course, you can always plan it out and avoid all this.

[MichaelBick]

Originally Posted by ksafin

Thanks for the quick replies guys, I'll forward all of this to our Mechanical Captain.

While I'm one of the more mechanically savvy guys on the team, the final call is to the captain

Also, another question/concern. With 80/20, we had the flexibility of just putting a drivetrain together with the parts, and then when we needed to change something or add something, it was a matter off adding a connector or taking this off or adding this. Very simple, with little modification.

I imagine that by using aluminum sq tubing w/ gussets and all, we'll have to plan our drivetrain out much more thoroughly than we did with 80/20 (unless we plan to have a lot of random holes from taking gussets off and on xD)

Is this correct, and how do you cope w/ this?

CAD, CAD, CAD. As you can tell I'm a CADder. In all seriousness though, the best way to get better really quickly is to start CADding. It allows you to build robots quicker and cheaper. Also in response to not having access to a waterjet, I reccomend that you find a waterjetting sponsor. Any 2d work is really easy to find a sponsor willing to do work for you, because the time commitment is a lot less for them that of a full blown machine shop.

[Akash Rastogi]

Originally Posted by ksafin

Is this correct, and how do you cope w/ this?

CAD

As Adam said, if you can't figure out how to make this stuff with manual tools (which you really should be able to) then get sponsors and learn how to CAD.

Call these guys. http://www.metalsupplyfl.com/

They are in your town, they waterjet cut, weld, and can do a lot of other fabrication.

Simple google searches and a phone is all you need to find sponsors. Just get up and do it.

Again though, I see no reason why you are not capable of making such parts with your current machines.