Input On Steel chassis w/wood inset

[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.

[evolution]

Still somewhat off-topic, but a quick technical question -- what are the wheels that 121 used made of?

[ChuckDickerson]

Originally Posted by evolution

Still somewhat off-topic, but a quick technical question -- what are the wheels that 121 used made of?

They look like they may be Colson wheels.

[Ellery]

We've used wood bases on all our bots prior to 2002 and they're been pretty durable and very convenient when mounting anything. But I decided to step away from wood if necessary to reduce weight.

As far as Aluminum Welding - We just had a complimentary TIG welding Class organized by Team 340 and it was an experience. It was alot harder than it looks.
Has anyone tried using this DuraFix stuff seen on TV and at trad shows? It's Aluminum brazing. I tried it on some easy butt welds and it seemed to hold up somewhat and can possibly used for small pieces with lower loads but I really had to crank on it to really break the first time weld I made.

This does require some practice with proper material heating and prepping but it may be an alternative if you don't have access to a TIG welder.

Just something to throw out there... It's a lot cheaper $40/lb of brazing rods from Durafix and only $8/ packet at harborfreight for about 8 -10 rods.


Let me know if you've tried this before.
Ellery

[Not2B]

Originally Posted by Ellery

Has anyone tried using this DuraFix stuff seen on TV and at trad shows? It's Aluminum brazing. I tried it on some easy butt welds and it seemed to hold up somewhat and can possibly used for small pieces with lower loads but I really had to crank on it to really break the first time weld I made.

This does require some practice with proper material heating and prepping but it may be an alternative if you don't have access to a TIG welder.

Just something to throw out there... It's a lot cheaper $40/lb of brazing rods from Durafix and only $8/ packet at harborfreight for about 8 -10 rods.


Let me know if you've tried this before.
Ellery

Yeah, I wondered about that stuff. It's not great. I could break all the joint I made with some good impacts and twisting.

HOWEVER...

Real Al brazing (with the correct flux) is easy enough to do with tools you can pick up at Home Depo (or others). The joints I made a few years ago are still together, and that's after I asked the team to try to tear it apart (with no tools.)

But you'll want to practice, practice, practice... I also like to rivit joints as a back up - belt AND suspenders approach.

[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.

[John Simons]

I think that you have an excellent idea with useing a steel frame, as long as you select the proper grade. Our team has been using a 4130 chromoly frame for the past few years and it has worked extremely well for us. First of all, it has a much higher modulus of elasticity than aluminum and therefore will deflect less in an impact let's face it that just tends to happen in these games. Secondly, it's fairly lightweight. I know that you thinking this probably can't be true, but it is. One inch square tubing with a 0.049" wall thickness is only about 18% heavier than 1" sq. aluminum tubing with a 0.125" wall thickness and has about 3 times the strength. Third, this will allow you to weld more easily. It can be welded with a standard MIG, although I do recommend TIG. Or if you're in a pinch or have electronics mounted on the frame it can easily be gas welded. If you want a real world example of where this material is used look no further than autoracing. Most roll cages are built out of this strong material and some vehicle frame are built with nothing but.

If you do decide to use this material you will have to do at least two things to ensure the longevity of the frame. Firstly, you have to paint or clear coat it because 4130 is highly susceptible to corrosion. And secondly I would recommend annealing the frame to reduce stresses that may have been introduced during welding.