our team is mildly considering a steel chassis with wood inset.
The steel would be very minimal, just a ridgity frame.
the wood holds the other things, battery, compressor, electronics, etc.
Drive motors + transmission would probably be attached to frame
Pros i can see (at least for our team):
welding at home- we do not have aluminum welding capibilities in our shop, and not having to ship our chassis off for everything would be nice
Overall cost is lower
shock factor. “yeahhh, our chassis is steel.”
Cons:
Steel = Über Heavy!
I would never ever use steel.
We used 1/8" steel angle for our frame in 2002, and it was an absolute beast.
Complete overkill, and kept us from being able to implement all the functions we wanted.
Mmmm, I think it’s probably up to whatever you think you need. However, I will give you a couple examples. Rage 173 used a completely plywood frame this year, and I believe they have for the past several years. This is from one of their engineering mentors at RampRiot, “We only had a few problems with one crosspiece breaking during build. If you spar it correctly it holds up fine”. And it did. It was a little dented, but not excessively for being through several competitions. We hit them a couple times, and they seemed no worse for wear.
Example #2: Many moons ago, in 1998, our FIRST year, we used welded steel conduit for our entire frame. It flexed a little, and was heavy, but it never failed at all. We did have to skimp on our mast, it was PVC, but it was done.
Aluminum is generally a very good stand between for frames, thats why almost everyone uses it, but wood alone, if properly designed, is very adequate. As I imagine, it’s less forgiving to design, but after it’s designed, it’s very forgiving as a frame material, on the field, and to fix in the pits.
Well, wood works well alone. Our '03 robot was entirely plywood and it did just fine.
well the last two years we have used wood, and last year the wood flexed giving us chain tension and sprocket alignment problems (in collisions the wood would flex and we would loose the chain 
)
one of our members was thinking to use aluminum angle to strenghten the frame, and i though an entire metal frame would be cool (partly inspired by swampthing, that thing is cool, if you haven’t seen it, http://www.chiefdelphi.com/forums/showthread.php?t=38184&highlight=swampthing)
Seeing that you have used wood in the past and have had some problem with it, I would suggest trying to make the change into an aluminum frame. If you want to. Several options. There are various extruded brands you could use, the kitbot frame, or if you could afford to constrain yourself at the beginning of the season and had the resources, a welded 1 piece frame is freaking awesome. Its cleaner, smoother, and more awe inspiring than anything else. (Until I see a one piece injection model plastic frame that is 
) But you might want to stick with one or the other, 1 type of metal, or wood. That way you don’t end up with stresses where the materials meet and have a bunch of headaches trying to reattach your angle to your wood components.
Henry:
I think that you might want to broaden your manufacturing thoughts a little. It sounds like you would like to use welding as the method to hold your frame together, and since you don’t have the capabilities to weld aluminum, you are considering using steel.
What I would propose is considering other methods of fastening your frame together. For a number of years on team 461, we used extruded aluminum from 80-20 and made our own brackets to hold the frame together. I was even known to advocate extruded aluminum over welded aluminum frames from time to time, albeit now I think that the weight savings and rigidity from welding aluminum is a greater advantage than the assembly ease and general flexibility of a extruded aluminum frame.
I would definitely advocate exploring extruded aluminum frame as an alternative to a welded steel one. Since steel has a density almost 3 times greater than aluminum and your mild steels are only roughly 25% stronger, it’s pretty hard to make an engineering case for using a steel frame. If a standard Aluminum frame would weigh say 7 or 8 pounds, I’d image the extra 14 or 16 pounds you’d need for an identical steel one would be stealing those precious pounds that always seem to run out all too quickly.
[Edit]: At the same time, while extrusion is relatively cheap, the t-nuts and other ‘add-ons’ can quickly add up (T-nuts run about $0.40 each). Steel is definitely your cheapest route.
[Edit #2]: Also, the kit frame I would imagine would be another alternative. Whatever complaints or concerns you could possibly have (and I’d imagine most concerns are quite design dependent) would defintely be something that could be resolved through re-enforcement, and would ultimately still have to weigh less than a steel frame.
Good luck this season!
Matt
well, i can tell you we won’t be using the kit frame.
if we can manage a solid welded aluminum frame, i think its the best option.
however, it may be a little out of our reach this year, and i was brainstorming alternatives
also, i had thought aluminum is more expensive than steel is, but i dont know if thats true
we are hoping to go to nationals and need all the money we can get
edit: what is “extruded” aluminum? does than mean angle?
edit #2: well, im sure we would go with reinforced plywood before the kit frame, unless it gets a lot better next year. I know this because we did it last year 
I personally wouldn’t use it because i think it looks bad and there are more sophisticated alternatices such as plastics.
In a pinch though, wood definately has a few advantages. Its readily availabe, can be “machined” extremely easily, is fairly light and strong and very cheap.
It would be really interesting to see a nice furnature quality mahogany robot. I built a teak computer and it looks sweet!
80-20 has some nice little demos you can see here:
http://www.8020.net/T-Slot-2.asp
Essentially the idea is that you can rapidly assemble a frame by using t-nuts that fit inside the channels of the extrude aluminum. No welding is needed, and components can be assembled and reassmbled numerous times. No drilling into the material is required either, since the t-nuts provided threaded holes to use.
And yes aluminum is more expensive than steel, but steel is very cheap. If you’re looking to buy box aluminum, you can get 8 feet of 1" x 1" x 1/8" for about $15. I’ll say you can get a frame out of roughly 20 or 30 feet.
Matt
I’m wondering what exactly your beef is with the kit frame.
It’s a pretty awesome way to get moving with minimal time and money investment.
Any particular reason you are discounting the kit frame so quickly? We used it last year with a plywood electronics board mounted in the center with great success. We went to the finals with you guys last year at Lone Star.
Ughh…I’ve got to say this. I was also once part of the "kit frame looks chinsy, feels chinsy, smells chinsy, must be chinsy’ club. However, through counseling, my teammates persuasion, and some actual competition smackdowns, I got over my affliction. That little chinsy bent aluminum frame took more than we could throw at it, which happened to be alot. After we hacked up it’s structural portions and even neglected to use all it’s reinforcing members. Yep, we were stupid, un-thourough, and yet it still never gave us any trouble. A team has every right to say they don’t want to use a free frame, but I urge them to build the kitbot and repeateadly smash it into a concrete wall in order to sate their anger. It will soon wane when they manage to do more damage to the wall than to the kitbot. That is honestly the reason that we ended up using the kitframe this year.
yes, the kit frame is a very solid start. My statement that we would use it if it got better was misplaced, it is definitley a robust frame.
However, i think that we can put in the extra effort to create a personalized base that meets all the specifications we want it to.
I don’t think the kit frame is low enough to the ground for my liking. does anyone know how much the kit frame weighs, anyway?
Edit: if i remember correctly, we were allied with 456 in the finals. Too bad we lost, though. unfortunatley, i do not remember you robot very well
Edit #2 : i need to learn to read, eh?
guess what? another edit! : i should have said we will not use the default kit frame
I don’t know exactly how much it weighs, but it’s comparable to an extruded frame of it’s size. Under 10 lbs. The idea of the kit frame is that even if you didn’t like to default setup, you could modify as you liked. We put blocks inside the rails and constructed our drivetrain from there, much lower to the ground.
It’s all in how you use it. 121 used the kit frame in a “low rider” conifguration with much success.
http://www.joemenassa.com/Images/ROBOTICS2005/Day38/images/IMG_7581.jpg
If you can’t weld Al (skill-intensive), and you don’t want to use 80-20 (expensive)…
Rivits! Pop rivets are good when used correctly. I love pop rivets. You can be pop riveting after a $16 investment at your local hardware store.
And for wood - that is nature’s composite. Most lumber only has the fibers (that resist tension) running in one direction. That’s seen in the grain. But you can get plywood with the sheets running 90 degrees from each other. When used correctly, in the correct applications, wood is good.
Basically - there is no correct answer - each application, each material, and each design need to be considered and evaluated based on what’s important to you. That’s engineering…
Edit:
Oh yeah, on the kit frame - if you worry about it’s rigidity, take a sheet of plywood and put it inside the C-channels to give it a solid wood floor. Bolt that sucker down, and the frame is going nowhere fast. (But the kit frame is DARN nice… and more modifiable than it’s given credit.)
IIRC about 13lbs total. Pretty good if you ask me especially considering how easy it is to use to get started and how much abuse it can take and how flexible it is and that it is free! I know our team could never design and build a frame as light and strong and flexible as the kitbot frame with the resources we have.
There are lots of ways to “lower” the frame if you want to. Flip it upside down and make some aluminum pillow blocks and you can drop it to the ground if you wanted to. Flip it upside down and slap a couple of the new IFI 4" wheels on there an you should be pretty low.
BTW: How do you know low is a good thing this year? Since we don’t know what the game is yet, low may be a bad thing.
I DO know (unintentionally) tipping your robot is allways a bad idea.
and we are not only not welding beacue its skill intensive, we just dont have a welder
however, if i tried it i would probably end up setting my hair on fire
1/8" steel pop rivets, T6061 1x1x1/8" aluminum angle and a drill will give you a tough box. 1/4" furniture grade birch plywood is tough and light. To kick the plywood up a notch laminate a layer of 6 oz. S fiberglass on one side with epoxy or real go for it and laminate both sides. Strong, lite and can be done with common hand tools.