Chassis Materials

[neoshaakti]

hey I was curious about what materials teams use to construct their chassis

and what material is the chassis provided in the KOP made of?

thanks

[Billfred]

From IFI's Kitbot page (http://www.ifirobotics.com/kitbot.shtml), the kit frame is made of 5052-H34 Aluminum.

To answer your other question, we use kit frame and a dash of plywood.

[DonRotolo]

We use the kitbot frame, along with aluminum for things that need to be strong, and Lexan (Not plexiglass!) for things that just need to hold things. We're experimenting with aviation plywood and composites for non-structural items to save weight. We'll sometimes use whatever seems to fit the bill.

Mostly aluminuum by weight.

Don

[vivek16]

aluminum and plywood.
aluminum frame and plywood for a covering of sorts was our last years design. we will probably use mostly aluminum this year.

-vivek

[MrForbes]

a couple of Arizona teams use fiberglass, you can get it as "pultruded" structural shapes such as I beams, channel, angle, etc. The 1/4" thick version is about as heavy as 1/8" aluminum of the same size, it's very tough (bounces back instead of bending), can be worked with hand tools, can be bolted together, painted, etc. The I beam works great for mounting wheels and protecting them well, and the channel works great for crossmembers such as across the end. Cost is a bit high because you have to buy long lengths and get it shipped by truck freight, but you can use the leftovers for next year's robot.

Surprisingly not many teams have tried it....

Aluminum works well too, it's strong, light, not too difficult to work by hand, and available in many many shapes. Except a 4" x 4" x 1/8" I beam :)

[lukevanoort]

For the last three years, we've primarily used aluminium for structural parts; in 2005 we used a slab of plywood to reinforce the kit frame and for mounting electronics, in 2006 electronics were on acrylic (never again...) with aluminum chassis reinforcements. Last year we kinda hybridized the two methods, some of the electronics were on polycarbonate and some were on a small piece of plywood; again, the plywood serve a structural stiffening purpose in addition to its mounting job, but this time we also had (smaller) aluminum reinforcements. In '03 and '04 the chassis were entirely plywood, and in 2002 and 2001 they were 80/20 aluminum extrusion. The all out plywood method works, but it can be a bit heavy, the same goes for the 80/20 frame.

[JesseK]

What's the most common grade of aluminum among FIRST teams -- 6063?

[MrForbes]

Which alloy you use depends on what you're doing with it. 5052 is good for making sheet parts that require some forming (such as bending), while 6061 is commonly used for extrusions and parts that will be machined, not formed.

[EricH]

Aluminum tube with a plywood base in between (for electronics and motors). We've never had a problem in my memory.

[AndyB]

269 has used 4130 Chromoly Steel now for the past 4 years and hasn't looked back.

It has three times the strength with about the same weight as aluminum.

We have primarily used 1/2" for areas with little side load or where weight is a concern. 3/4" is used on our chassis although I think we've used 1" as well in the past.

http://aircraftspruce.com/catalog/mepages/4130square.php

We are surprised that we are still the only team, to our knowledge, to be using this stuff.

The only downside to this stuff is it goes through drill bits and drill batteries like crazy. I think we replaced our bansaw blade this year 1 or 2 times this year as well. We just bought a corded dewault so drilling should be much easier. We always use .035" thickness. We have never had a break.

If you buy this stuff, they give you welding rod as well. Although I don't know if we've ever used it.

[AdamHeard]

It has three times the strength with about the same weight as aluminum.


It's about 3 times heavier.... but, it is offered in thinner wall thickness than aluminum usually. But still, it's a good deal heavier.

294 used the kit frame in 05, a welded 2x1 extrusion frame similar to 4/22/60/254/968 in '06 and a plate sandwich concept (similar to 233 in 2006) for '07 and our current prototype.

[lukevanoort]

What's the most common grade of aluminum among FIRST teams -- 6063?
I'd wager that 5052-H34, 6061-T6, 6063-T52, and 6105-T5 are the most common alloys: 5052-H34 because it's in the kit; 6061-T6 because it's an excellent balance of price, availability, and strength; 6063-T52 because it's cheap and available (not too strong though...); and 6105-T5 because that is what 80/20 makes their extrusions out of. Personally, I like 6061-T6 for the reasons I've listed, but I wouldn't say no to some nice 7068 or 7075!

It's about 3 times heavier.... but, it is offered in thinner wall thickness than aluminum usually. But still, it's a good deal heavier.
I dunno, I think it depends heavily on your heat treatment. From some numbers I'm looking at on MatWeb, it seems that some (hardened) 4130 steels are about 2.9 times the weight of 6061-T6 aluminium, while being 3.5 times stronger. So, its strength to weight ratio seems a bit better. However, annealed 4130 and 4130 that hasn't been hardened that much are a different story; the less hardened versions are only about twice the strength.

[MrForbes]

Steel is 2.8 times as dense as aluminum, it doesn't matter what alloy. But strength DOES depend on alloy and treating, and you can find steels that are several times stronger than some types of aluminum...and you can also find aluminum alloys that are several time stronger than mild steel! so you have to be pretty careful in you comparisons, to make sure you are comparing apples to apples, and oranges to oranges.

1501 has used chrome-moly steel tubing.

If you are interested in keeping your robot from falling over, go heavy on the chassis, and save the exotic materials and super lightweight design for all the "up top stuff", such as arms, etc.

[cooker52]

But don't go to heavy, otherwise you will come up at the last minute drilling holes in everything.

As for us, we did use some chromoly this year. For the most part, we use 6061 aluminum. We use the sheets of aluminum and bend and curve it into our robot's form. This technique of making a uniform body is called monocoque and it is very light weight and durable.

Here's a picture of last years (2006) robot.

[AdamHeard]

If you are interested in keeping your robot from falling over, go heavy on the chassis, and save the exotic materials and super lightweight design for all the "up top stuff", such as arms, etc.

Good advice for rookies, but I still cringe every time I hear you say that.

I prefer to lighten everything as much as possible AND keep the weight low. That way your not wasting any weight just to get a low CG. Some teams are amazing at that (469 and 1114 come to mind this year)...

If you lighten your frame by 5 lbs, and that frames CG is 3 inches above the floor, and you then mount 5 lbs of something anywhere below that 3 inches, your CG is lower.

But in the end, there's nothing wrong with your idea.

[M. Mellott]

Team 48 has used welded aluminum box tubing for our base frame for years, 1/8" wall for the outer box and 1/16" wall for inner bracing. Aluminum takes some practice to weld, both to weld it with proper penetration without burning through it, and to weld it without warping the frame. We've had ours welded up at a local machine shop before, but last year one of our team member's father who works at a steel mill offered his services.

We feel the base frame, the foundation for your robot, is very important to make as solid and strong as possible, even if it means spending an extra couple pounds. That way, it's one "sub-system" that we don't have to worry about down the road, even after many matches. The last thing you want is to have to tear apart your robot to repair a bent/broken frame in the middle of a competition--it could make for a long weekend.

[joeweber]

The 2004 and 2005 season we used HDPE. Pictures @ http://team1322.org/pictures.htm It can be heavey but it has alot of give. This was befor bumpers, other robots would just bounce off with out damage. We found a local place that would weld the plastic together.Our robot was completly plastic except the arm. The plastic was very easy and safe to work with, students could cut it and not get shavings in there skin or cut themselves on the edges. You could use a jig saw, router, hand saw, and drills with ease. We still use HDPE (High Density Poly Etholean?) as mounts for motors or structure supports between aluminum frames. This seasons robot we used two blocks 2.5 x 5 x 6 in. and cut it into a fun looking "Y" to get around some items so we could mount the motors in a particular spot. The stuff is strong and easy to work with. Also you can use it as a low speed axel support or make pillow block out of it. Look close at this picture @ http://team1322.org/DSC00703.JPG you can see the motor mounted to it.

[redbarron]

Team 1270 used 6061-T6 4"x4" box tubing (3/16" wall) last year and we are using it again this year. We integrated the AM Transmission with the whole drive train into each side tube. The CG of the bot with the tube 113 inches in the air was in the center of the robot and about 7 inches above the floor, we didn't add any extra weight or heavy materials to the base just kept as much of the weight as low as possible.

[falconmaster]

http://www.creativepultrusions.com/

Pultruded Fibergalss

1/5 the wt of steel/ 1/3 of alluminum for same strength!
Electromagnetically transparent
Non conductive
non corrosive

the best stuff!

[JesseK]

http://www.creativepultrusions.com/

Pultruded Fibergalss

1/5 the wt of steel/ 1/3 of alluminum for same strength!
the best stuff!

What's the cost compared to 6061 Aluminum? I'm thinking along the lines of 1" square tubing that's 1/16th thick for aluminum (since we know it's strong enough) vs. 1" square tubing that's 1/8" thick for the fiberglass.

Also, what do you use to reliably "weld" the components together? Also, being that you're from a NURC team, how well does this stuff hold up under water?

[falconmaster]

If you sand it epoxy works great. We use 1/4" bolts with 3/8" lock nuts, and it works great. We use all the same size nuts and bolts. You need stainless for the underwater bots!

In most cases the cost is more, but not that much more, especially if you count in the labor time and repair time you save.
1 1/2" x 1 1/2" x 1/4" is $2.74 a foot

1" x 1" x 1/8" $1.20 per foot

6" c-channel $7.34 per foot

The water has no effect on the material at all!

[Molten]

If you are interested in keeping your robot from falling over, go heavy on the chassis.

I definitely think he has a great point. Alot of teams struggle with weight, but we have never had troubles. We use 1 1/2 inch aluminum tubing. I remember our first year(2006). We was at the Boilermaker regional and a team made it to the final rounds(I think). And their robot fell apart on them. I felt so sorry for them. They made a great robot, but they did not consider structural integrity as much as they should. Our robots have been tipped time and again, and we have yet to see any damage. So, worry about weight. Just not as much as the structure.

[Doug G]

Oh so many techniques and materials...

2001: We used Bosch 30 series extruded Aluminum (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/2000-2001/00-01/images/Final_Assembly_5.jpg)and steel sheet metal for mounting the lightweight components. The connectors for the Bosch got to be a bit pricey.
2002: We switched to 80/20 1" extrusion and T-nuts and such (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/2001-2002/images/RobotFinalDay10.jpg). Great for new teams, easy to make adjustments. But in the end it can get used for too many things and your robot is heavy. Used 1/8" Aluminum plate to mount things to.
2003: 80/20 Extrustion 1" extrusion again (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/Pics/BuildPics/robot_guts1.JPG) with some 1" Al angle here and there. Used 1/4" Lexan to mount electronics to.
2004: 1" Al 6061 Tubing (1/8") (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/DSC02160.JPG)welded together by students. Used 1/8" Lexan to mount electronics.
2005: 3/4"x1.5" Al 6061 Tubing (1/8") and C-channel (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/Pics/04-05/BuildSeason/DSC00357.JPG)welded by students. Used 1/8" lexan for mounting components
2006: 1"x2" Al 6061 Tubing and C-channel (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/New%20Site/pics/week4/images/DSC02945_JPG.jpg)again welded by students. 1/8" Lexan for the electronics
2007: 1"x2" Al 6061 Tubing and C-channel (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/New%20Site/pics/06-07/BuildSeason/Week4/images/DSC05061_JPG.jpg)again but welded by sponsor. Custom made Fiberglass panel (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/New%20Site/pics/06-07/BuildSeason/Week4/images/DSC05112_JPG.jpg)that when under the robot. Used 1/4" foam core and included hard points for mounting compresser and electronics. Now we now how to do this, we will be doing this each year.

[legotech25]

We used 1/8" polycarbonate for the entire robot, including the chassis!!! :yikes:

[joeweber]

Do you have a link to Pictures, I have though about using it, kind of like unibody construction ?

[Rapt0r9]

We always used some type of aluminum. Whether is it 80/20 or the kit frame, rarely do we need to use anything else. Ocassionally we have used harded steel for things that need to be extremely strong and we used lexan for all of our electrical work, but if you saw our robot this year, you would understand what I mean when I say we are all aluminum.

[MrForbes]

Do you have a link to Pictures, I have though about using it, kind of like unibody construction ?

go to google.com

click "Images" at the top left corner, then type

FRC 1714

into the box, and click "search images"

you'll find lots of pictures of their neat robot, and links to the morerobotics web page.

(note that this search technique works for finding pictures of just about anything you want to find pictures of)

[joeweber]

Thanks, Looks good, I wished their site had some thumb nails of the robot so I could get a closer look.

Off subject: Is their a site with a picture of every teams robot. Wouldn't that be a good idea for the First web site, when you enter you teams info you could also add a picture of your robot when it is built and first could forward it to a Page with every teams robot per season.

[MrForbes]

I agree that that is a great idea, my guess is that others have tried to do it but have not succeeded, because it is a daunting task!

When our team goes to regional competitions, I take pictures of all the other robots the first day, and put them on our web page that night. I doubt this happesn at every regional event though, and I haven't tried to coordinate my efforts with those of other people.

First place I'd look would be

http://www.thebluealliance.net/

[JesseK]

Oh so many techniques and materials...
...
2005: 3/4"x1.5" Al 6061 Tubing (1/8") and C-channel (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/Pics/04-05/BuildSeason/DSC00357.JPG)welded by students. Used 1/8" lexan for mounting components
...


I noticed that you use nylon/plastic sprockets on the drive train. How did that work out for you, were they strong enough to last the whole season?

[Doug G]

I noticed that you use nylon/plastic sprockets on the drive train. How did that work out for you, were they strong enough to last the whole season?

Absolutely!! In fact we only recently dismantled that robot. The only part on that drive system that gave us a problem was the #10 bolts used to bolt those sprockets on, they would break about once a year. Don't be fooled about the #35 nylon sprockets that are available - #35 is usually overkill in many drive systems any ways. We tend to keep using it because you can get away with some misalignments here and there.

We used the nylon sprockets in 06 also (http://www.travisusd.k12.ca.us/vanden/clubs/robotics/New%20Site/pics/week%206/pages/DSC02990_JPG.htm)... In 07 we went with the Aluminum plate sprockets from AndyMark - you know the ones with the bolt circle pattern already drilled in them.