Input On Steel chassis w/wood inset

[Henry_Mareck]

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!

[Cory]

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.

[Andrew Blair]

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.

[Henry_Mareck]

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/sh...ght=swampthing)

[Andrew Blair]

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_Mareck]

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

[Matt Adams]

Originally Posted by Henry_Mareck

also, i had thought aluminum is more expensive than steel is, but i dont know if thats true

edit: what is "extruded" aluminum? does than mean angle?

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

[Not2B]

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.)

[Cory]

Originally Posted by Henry_Mareck

well, i can tell you we won't be using the kit frame.

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'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.

[Henry_Mareck]

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

[Andrew Blair]

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.

[Karthik]

Originally Posted by Henry_Mareck

I don't think the kit frame is low enough to the ground for my liking.

It's all in how you use it. 121 used the kit frame in a "low rider" conifguration with much success.

[greencactus3]

Originally Posted by Karthik

It's all in how you use it. 121 used the kit frame in a "low rider" conifguration with much success.

slightly offtopic but while we're on rideheight, what is the minimum ground clearance most people would attempt. assuming the playing field is a completely flat surface or carpet. and using pretty solid tires not spongy ones or pneumatic ones. ones with very little give.

[Cory]

Originally Posted by greencactus3

slightly offtopic but while we're on rideheight, what is the minimum ground clearance most people would attempt. assuming the playing field is a completely flat surface or carpet. and using pretty solid tires not spongy ones or pneumatic ones. ones with very little give.

I'd say probably at least 3/4 to 1", given that the floor might not be completely level, and you might encounter other unexpected obstacles.

For instance, you could have bottomed out on the HDPE triangles in the loading zones last year, without a bit of clearance.

[gburlison]

Originally Posted by greencactus3

slightly offtopic but while we're on rideheight, what is the minimum ground clearance most people would attempt. assuming the playing field is a completely flat surface or carpet. and using pretty solid tires not spongy ones or pneumatic ones. ones with very little give.

Last year we designed for 1\2" and ended up with 3/8" since the tread compressed more than we expected. Anytime you have to reach high, you need a low center of gravity. On the otherhand, for 'First Frenzy-Raising the Bar' we had more than 6" of ground clearance, but placing the battery below the axle, helped lower the center of gravity.