Input On Steel chassis w/wood inset
 

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!

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

Well, wood works well alone. Our '03 robot was entirely plywood and it did just fine.

Re: Input On Steel chassis w/wood inset
 

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)

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

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 :D

Re: Input On Steel chassis w/wood inset
 

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!

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

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.)

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

They look like they may be Colson wheels.

Re: Input On Steel chassis w/wood inset
 

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

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

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.

Re: Input On Steel chassis w/wood inset
 

Oh yeah, structural foam is the bomb. We also put wooden dowels inside tubes - the REALLY SMALL bit of added weight is nothing compared to the massively increased structural stability; I swear RaPHael (our robot last year) would have had its tube-based arm destroyed many times over if it wasn't for the wooden inserts!

And Henry, unless you know something I don't know (I won't discount it, I didn't go to the drive train meeting), we've always had our aluminum frames TIG welded by Randy Baden - remember "Randy the Welder"? :D

Also I want to give a shout-out to team 456, it's always a joy to see what you guys come up with every year - so far "Captain Hook" has been my favorite. Can't wait to see you again at Lone Star!

-Danny

Re: Input On Steel chassis w/wood inset
 

Hey Danny, a big shout-out back to 418! Unfortunately, we are going to miss you guys and everyone else at Lone Star this year. We let the team vote on what regional they would like to attend and we decided to try somewhere new this year just for fun. We are heading to DENVER! I have a feeling it may be a bit colder than Houston. We will miss everyone at Lone Star but are looking forward to meeting some new faces in Denver. Best of luck to you guys in Houston! Your bot ROCKED last year!

-Chuck

Re: Input On Steel chassis w/wood inset
 

I know it has been mentioned before, but I haven't seen much about teams using carbon fiber in frame construction. The way I see it, carbon fiber tubing from McMaster is reasonably priced, but has very thin walls, perfect for some filling with aforementioned structural foam. Combine it with some bullet resistant polycarb, maybe a little Kevlar or Ti, silver conductor wiring, and you'd have plenty of shock value... no money though. Seriously, that carbon fiber tubing looks great for arms, and if only I could find a good sorce of silver wiring I'd be pushing that through on my team at this very moment.

Re: Input On Steel chassis w/wood inset
 

the problem with carbon fiber on McMaster-Carr is that it is sold in very small amounts; the tubes are 1 ft long, and the sheets and plates are 2 ft or less. besides, where's the fun in using composites if you're not making monocoque, high temperature, vacuum bagged-parts?;)

Re: Input On Steel chassis w/wood inset
 

In 2004 Team 1114 used carbon fiber tubing for our gripper.

http://www.firstrobotics.uwaterloo.c...rms/arms83.jpg

It wasn't called for in our initial design, but after a couple iterations, we soon realized that weight was a huge issue for our team. We needed a lightweight gripper to ensure we fell within the weight limit, and to lower our center of gravity.

The carbon fiber tubing solved our weight problem, but we quickly realized that it wasn't going to be rugged enough to last for many matches. Knowing this, we designed the gripper so that individual portions of carbon tubing could be swapped out very quickly. This modular design allowed us to deal with the frequent breaks. (IIRC, a certain college team from somewhere in NY state snapped our gripper during a practice match... ;))

So, if you're going to use carbon fiber tubing, consider filling the tube with some sort of structural support, and be prepared with spares.
We ordered our tubing from Aerospace Composite Products. They have a variety of thickness, diameters and lengths when it comes to tubes. I believe we ordered the 60" sections. They shipped to us overnight (yes, across the border!), and were a pleasure to deal with.

Re: Input On Steel chassis w/wood inset
 

The price of true structure carbon fiber can be a budget buster. Mcmaster carries a selection of fiberglass pultrusions that are more budget friendly. Instead of thick wall material. Try tube in tube construction with 2lb expanding foam between the tubes. As this post was about wood and steel, I'll stress again that birch plywood is tough and can be reinforced with fiberglass. You find that the end result is a material that has better properties that polycarb and is lighter. Make sure the plywood is solid birch ply's and not a filler in the center.

Re: Input On Steel chassis w/wood inset
 

4130 steel is a great structural material. Alot of smaller planes have this chromoly frames. OOOh ya and planes have to be light right??

Welding aluminum frames is not very good. When you weld Aluminum the T6 hardness goes to T0 in the welded areas losing most of its strengh.

The bolt together extrusion is a very good way to go. easy to cut and bolt together Very Very strong.

The way my team(Rage 173) is has been going for the last 6 years is using 1/2 cabinet grade plywood. Really nice to work with. When its painted up it doesn't look like some structural monster.

I've been doing this for almost 11 years I've tried all these paths.
And the best 2 are the bolt together 80-20 extrusion and the plywood bases.
I would stay away from the welding its not necessary.
theres lots of manufactures of the extruded aluminum 80-20, bocsh profile, its pretty good. Its just grown up legos.

A first time team should either use the kit frame of go for the extrusion frame which is more stiff.

The plywood is nice but you have to know what your doing.

I have seen alot of welded frames in the competition do well but they really have to be over built to survive the punishment. They'll probably be someone that goes against my statement but the fact is the weld goes to Tzero!!! and the weld turns out to be the weakest spot. They might say they reage the welds by solution heat treat. but most likely not because the heat treat will warp and twist the frame.

The carbin fiber idea is all cool and fancy sounding but its really to brittle.

So if your a beginer go with the profile (extrusion) or if you have a really good carpenter take the leap and go with the 1/2 cabinet grade plywood.