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.

[Akash Rastogi]

Look for local sources for affordable pricing of 1x1 and 1x2 aluminum tubing. If you can find a local source who is willing to donate material, that is even better. If not, you can find great deals at www.onlinemetals.com

Tubing can be connected using gussets or by welding. A great example of the gusset method is Gus team 228 (no pun intended)

http://www.team228.org/media/pictures/view/4896

Check out the way they connect their corners using what I think is 1/16" thick 6061 aluminum sheet. I personally love this method because it is easy for teams to do without much (if any) precision machining. You can CAD up a design for your brackets, print out 1:1 scale engineering drawings, and just use the print out as templates for pieces to cut on the bandsaw and make a hole pattern with a drill press. A lot of teams use this method along with rivets but you can also use screws and bolts. Don't use something bulky like 1/4-20 though. Rivets are recommended.

Hope that helps!

[msimon785]

I have some thoughts of my own on the subject, but I think I'll leave you with this instead (from CD user BJC from Team 33)

[Garret]

If you can get a welding sponsor welded tube is one of the easiest ways to go (at least for my team welding is faster than rivets and gussets). We have built robots on budgets of ~$2000-$3500 for everything (spares, prototyping, tools, and so on) using the tube. If you use 1" square 1/16" wall aluminum tubing you can build your robot structurally in much the same way you would with the extrusions but with a much lower weight and cost. Considering our machining resources usually are about the same as what you described transitioning to welded frames of thin-wall tube should be relatively easy (if you can get a welding sponsor, otherwise do gussets and rivets/bolts).

[MichaelBick]

Originally Posted by Akash Rastogi

Look for local sources for affordable pricing of 1x1 and 1x2 aluminum tubing. If you can find a local source who is willing to donate material, that is even better. If not, you can find great deals at www.onlinemetals.com

Tubing can be connected using gussets or by welding. A great example of the gusset method is Gus team 228 (no pun intended)

http://www.team228.org/media/pictures/view/4896

Check out the way they connect their corners using what I think is 1/16" thick 6061 aluminum sheet. I personally love this method because it is easy for teams to do without much (if any) precision machining. You can CAD up a design for your brackets, print out 1:1 scale engineering drawings, and just use the print out as templates for pieces to cut on the bandsaw and make a hole pattern with a drill press. A lot of teams use this method along with rivets but you can also use screws and bolts. Don't use something bulky like 1/4-20 though. Rivets are recommended.

Hope that helps!

I also think 973 does this well. Also one thing to point out for lower resource teams is that if you get the gussets cut accurately(with a waterjet sponsor namely, which are really easy to find) you can match drill your whole robot frame

[AdamHeard]

Originally Posted by MICHAELABICK

I also think 973 does this well. Also one thing to point out for lower resource teams is that if you get the gussets cut accurately(with a waterjet sponsor namely, which are really easy to find) you can match drill your whole robot frame

Yes, our entire 2012 robot (and various parts of older robots) were held together with gussets, not welding.

We made our own cnc router, so the ability to cut arbitrary gussets in house on zero notice was helpful.

Your suggestion of having a sponsor cut gussets is totally valid, a waterjet or laser will fly through 1/16" plate.

[DampRobot]

Originally Posted by AdamHeard

Yes, our entire 2012 robot (and various parts of older robots) were held together with gussets, not welding.

We made our own cnc router, so the ability to cut arbitrary gussets in house on zero notice was helpful.

Your suggestion of having a sponsor cut gussets is totally valid, a waterjet or laser will fly through 1/16" plate.

Just to add in, even if you don't have a waterjetting/CNC/laser cutting sponsor, you still can do the work yourself at a local hackerspace. We're planning on cutting our gussets and bellypan with a hackerspace's waterjet, rather than milling them in our own shop (which took forever).

In our experience, gussets are a great way to save weight (because you can use thinner wall tubing), but rigidity is compromised. I'm hoping to in house weld our drive base again for the sake of rigidity, but I'd concider doing riveted gussets on our superstructure again, even though our tower was a but wobbly last year.

As a final note, don't have freshman make all your frame pieces in a drill press and expect all the holes to line up. Take the time to CNC the frame members, to have experienced members do the drilling, or be prepared to have these same freshmen do a lot of filling...

[Mk.32]

We recently switched over to a box tube + gusset bolt together construction method: http://www.chiefdelphi.com/media/photos/38147

It's a great way to put together a stiff and strong frame that is also light, our entire frame was under 20lbs.
Using rivets instead of bolts will help a lot with weight as well.

[Cory]

Originally Posted by DampRobot

We're planning on cutting our gussets and bellypan with a hackerspace's waterjet.

I assume you're referring to Techshop.

Unless you've managed to get them to sponsor your team, or your baseplate is vastly simpler than ours, it would be extremely expensive to jet one there. Probably on the order of $500-750.

[AlecS]

Originally Posted by Cory

I assume you're referring to Techshop.

Unless you've managed to get them to sponsor your team, or your baseplate is vastly simpler than ours, it would be extremely expensive to jet one there. Probably on the order of $500-750.

The current price is 2$ a minute of pump time for members at SJ. 1323's bellypan last year was about 45-50 minutes a piece on a similar sized waterjet, so it would probably come out to about $200 per. Not super cheap, but I've had laser shops charge more than that just for setup even with a discount.

[AdamHeard]

Originally Posted by Mk.32

We recently switched over to a box tube + gusset bolt together construction method: http://www.chiefdelphi.com/media/photos/38147

It's a great way to put together a stiff and strong frame that is also light, our entire frame was under 20lbs.
Using rivets instead of bolts will help a lot with weight as well.

Ditch the bolts and as much 1/8" as possible, we've never had a frame over 10 lbs

EDIT: I'm referring to drive frame and superstructure frame separately.

[Mk.32]

Originally Posted by AdamHeard

Ditch the bolts and as much 1/8" as possible, we've never had a frame over 10 lbs

EDIT: I'm referring to drive frame and superstructure frame separately.

The tower is all 1/16th but the drive mostly 1/8th. We are planning on switching over to 10# hardware and 5/16 rivets.

[R.C.]

Originally Posted by Mk.32

The tower is all 1/16th but the drive mostly 1/8th. We are planning on switching over to 10# hardware and 5/16 rivets.

3/16" Right

-RC

[Mk.32]

Originally Posted by R.C.

3/16" Right

-RC

Maybe......