Input On Steel chassis w/wood inset

[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.

[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.)

[ChuckDickerson]

Originally Posted by Henry_Mareck

yes, the kit frame is a very solid start.
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?

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.

[Henry_Mareck]

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

[Gdeaver]

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.

[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

[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.

[sanddrag]

Chromoly is a bit expensive though and not every metal store stocks it.

Aluminum seems to be the material of choice for FRC robot frames. I don't like hearing "we don't have a TIG so we can't have a welded frame" I hear this far too often. What you should be saying is "we want a welded frame so we're going to find ourselves a sponsor or volunteer with a TIG" Don't say "we can't do it so we won't" say "we can't right now but we sure want to so we will find a way" We don't have a TIG welder, heck, we don't have any welder, but for the last two years we have had a beautifully TIG welded frame and we didn't pay a dime to get it done. There are people out there who can help you out, you just have to let them know your situation.

If you try to make a welded aluminum frame happen and you just can't find anyone willing to help you out with the TIGing, then try to design a bolted or riveted together frame. I bet it will work better than you may think.

[lukevanoort]

Also, for any type of tube or sort of tubish frame, you can stiffen it with structural foam. Just spray it in and let it dry, and you have rigidity, however, I have no idea how much it costs/weighs. For other methods, look at the tuner aftermarket for sport compacts. A Civic or Lancer is about as stiff as tissue paper, but with proper chassis braces they can be stiffer than most sports cars. If you're dead set on saying "we have steel" then a steel tube or bar hammered flat at the ends with threaded holes drilled in and bolted to the kit frame can greatly stregnthen your chassis. Mind you, if you want shock factor I'd advise the material on page 3361 of the McMaster catalog, a bit hard to work with, and it can be hazardous sometimes, but it'll definatly get noticed.

[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.