I was curious on what is the best material for building a frame for a robot. Last year, we used 1" aluminum tubing and it did well but it was difficult to weld and it was not as strong. I see other teams using extrusion tubing and I was also curious on why extrusion so good. Thanks for your help!
There are many different types and kinds also sizes of extrusion that your able to get. One reason we used extrusion last year was the ease of it compared to making all the frame with the 1" aluminum like we did in 2003. It cut back on time, money and human resources because all we had to do is call the nearest dealer and they would send us a piece for our frame instead of cutting and welding the pieces together. The nuts and bolts that the extrusion come with are very strong and hold up through many competitions if used correctly. here’s a website that i have as a favorite from last year, even though we never ended up using them we had a dealer about a half hour away that was very generous to us. I hope all of this helps you and can’t wait to see what your team builds this season.
Pit Bull
P.S. If visiting the website go towards the bottom for the FIRST special…
I agree with most of what Pit Bull said about extrusion. It is very easy to work with and is very strong. However, it is very heavy. When teams have only 130 pounds to work with every pound counts.
For about three seasons or so Cyber Blue used extrusion, but this previous year we went with aluminum tubing. It worked out very well for us and in the future I’m sure we’ll do the same.
Yeah extruded alumnium is pretty easy to work with as long as you don’t need anything welded. We used 30mm X 30mm Extruded aluminium for all of our robots. There’s also 20mm x 20mm Profile that we also used in the previous two years for various parts of our robot to reduce weight. Both of them are very durable, We never hand any problems with it breaking or bending.
Another problem with aluminum extrusion is that the connecting pieces can get kinda pricey. This can be a problem for teams with limited funds, but you can always make your own connectors, as most companies give dimensions in their catalogs. Just something to think about.
yeah, we (Team 435) have used extruded aluminum for about 4 years now. It is very useful, because it is durable, and you can easily move pieces around. If you make an incorrect measurement, you can simply loosen the pieces, and slide them to the desired location. For the last three years, we used BOSCH, and for the 02, and 03 seasons, we used a combination of 30mm x 30mm, and 20mm x 20mm. Last year, we switched to their 1" system, because that is what all the rules and parts are in. Switching to 1" was a welcomed change.
-Sam
We have used angle aluminum for the frame for the last 2 years and have had very few issues. it is light and somewhat durable. However we did break a few pieces but that was from defending the king of the hill in the stack attack game, where at times it got rough. It is easy to work with, its light, but isn’t as strong as extruded or square.
Aluminum Plate and standoffs!
…thats if you have access to machines to cut the parts you would need.
KISS!!!
One of my favorite materials is the 1 in square aluminum tubing but you don’t weld it together. There are a number of sources of reinforced nylon connectors that insert into the ends of the tubing and lock it together. For extra strength you can drill through the assembly and reinforce with a pin, rivet or bolt. The connectors come in a variety of shapes and are nearly indestructible. Our 2002 robot Silver Scorpion was made of this material and it still runs like a champ. And believe me, our robots have been flying bricks that take a real beating on the field.
Team 25 has been playing around with different frame materials for the last few years and we’ve ranged from 1/4 in aluminum sheet shaped and cut out through the tubinig and extrusion, aircraft foam ( remember 1997?) and plywood. The plate works pretty good but you need to assemble the layers with spacers and lots of screws. In essence we make a set of modular drive trains that are bridged by a simple cross frame and lots of screws. Take out 20 screws and a few electrical leads and the whole side of a robot is replaced in ten minutes. We hold drills with the kids in building the gearboxes from piles of parts much the way the army trains soldiers to assemble their rifles.
Extrusion is what we are looking at for this season, just to try it out. Our friends at 1089 used it last year and it worked well despite the exorbitant cost for the connectors. My BMS engineers have been talking about it and they seem to have an idea in their heads - January is coming soon!!
BTW- we have found that bolting parts together rather than welding gives the robot a bit of flexibility when it takes a hit. You can always replace a lost bolt but have you ever tried to fix a weld in aluminum in the pits? Ouch.
WC
for teams looking to easy construction you can also use steel tubing…now before you react to say that i am crazy think about this.
a piece of carbon tube steel (1/8 wall) .5" x .5" x 36" weights 1.5 lbs
a piece of 6061 alum tube (1/8 wall) 1" x1 " x 36 " weights 1.4 lbs
the weight difference between alum and steel is not very much when the steel is half the size
for teams who want an easy material to work with without having to buy all the attachment components with extrusion, think steel. much easier to weld, much less expensive, locally available everywhere, easy to machine
you might want to consider this when looking at materials for the upcoming season
This question isn’t really as straightforward as it sounds. There are really three parameters that determine the suitability of a framing material:
- Strength
- Weight
- Ease of use
Our team has used both Al square stock and extrusion so I can only speek for these two options.
Square stock
Square stock is relatively light and more than rigid enough for a first bot. If you are one of those supposed teams that designs a robot entirely and then assembles it in the last week of the build and it all works properly the first time then this might be a great choice. For the rest of us who are constantly changing things squarestock can become a problem. It very hard to move things that are welded on. If you are looking for strength then this might be the best option. If you are looking for flexibility then look somewere else.
Extrusion
If money is not an issue then this stuff is great. It is probably one of the best thigns our team has ever done. If you need to move something just loosen a bolt. Its very convenient. If flexibility is your goal then this would be the way to go. A word of warning: extrusion has very little torsional rigidity. It can take other loads fine.
If I recall right, our robot used the 2x4s in the kit. Heavy, but solid as a brick.
My team used extruded aluminum the first 2 years, but it was way to heavy which made us look for an easier base material. The past 2 years we have used a producted made by cooper/b-line. It is designed like U channel or back to back U channel but stronger. It is very easy to use, and it has brackets that help with the initial frabrication before welding. It is also very light and strong. Here’s the website, it describes it better than I can: http://www.b-line.com/. I doubt that we will ever go back to extruded for the base. As for now, we’ll keep that for telescoping arms.
Our team uses the 2 x 4 square tube from the kit. We cut it in half and end up with 1 x 4 “C” channel. There is enough to make all 4 sides. We have bolted and welded it together. It is light,strong, and comes in the kit. Hey, Race what ya got.
Our team (93) has gone through many of the design iterations that other teams have gone through. Wood and PVC tubing to aluminum angle to aluminum tube to unistrut (extruded profile).
We’ve chosen to stay with the unistrut for our base/drive frame because it really can take a hit and maintain it’s shape. And judging from the evolution of the FIRST game, high-impact is going to be here to stay!
This past year we experimented with fiberglass reinforced plastic or FRP. One of our structural engineers clued us in to it’s incredible strength to weight ratio and we used it on many of the upper structural components on our 2004 robot. The light weight kept our CG much lower than if we had used unitrut or even aluminum tubing up that high.
For connections we machined unistrut down to a size that allowed us to slip it in the end of the FRP with just a snug interference fit and used unistrut fasteners to tie it all together. On a side note we also made extensive use of nylon bolts and nuts and, much to my surprise, they held up quite well. I can’t recall a single one failing in competition. You’d be surprised how much weight you can put into fasteners on a FIRST robot and switchig to nylon really helped us out.
One benefit to the FRP (and this carries over to aluminum tube as well) is the ability to route electrical and pneumatics through the frame members to keep them out of harms way and give your robot a neat, clean appearance. Make sure your design is sound, if you have to replace a structural component that has elec/pneu running through it, you want to be able to do it quick!
Another benefit of the FRP is that when it takes a hit it flexes and returns to it’s original shape. Aluminum, on the other hand, won’t return if bent too far.
The FRP held up VERY well for us and we only had one frame member (not critical) crack on us. It didn’t break completely but it must have taken a good hit from the corner of another robot. And if you remember our robot from 2004 (the big green and blue laundry basket) we took a lot of hits from teams trying to move us out from under the ball drop.
If you’re looking for a different material to use on your robot, consider FRP. It’s pretty sweet stuff!
Sean
I gotta agree with greg on this one… we have used NOT STEEL but aluminum tube… as long as its welded right… you are good to go… most of the years out bots has been a pushing bot… probably at the end of the season we will see one or two bends but nothing really bad. Extrusion are good too… we have used it during 2002 season and it worked great… 
High quality plywood is a great material to seriously consider, especially if metal fabrication is a difficulty for you. One of the great things about plywood is that it doesn’t dent-- give it a hard jar and it will spring back every time. Often the plywood comes out of the season in better condition than the 1/8" wall aluminum box beams. I must admit though, for “shiny factor” our team is considering moving into a different material for next season.
Sorry but it looks like I beat you by about 2 years in starting this thread http://chiefdelphi.com/forums/showthread.php?t=14231&highlight=chassis+materials That’s okay, it was buried anyhow. Brandon, perhaps we should merge? Or not?
Buzz 5 (2000) used welded angle…I wasn’t on the team and don’t know a whole lot about Buzz 5, so I can’t comment on it.
Buzz 6 (2001) was extruded aluminum. It was good, but heavy. The way it was built, it was another one of those flexible robots, you can pick up a wheel and have the other 3 on the ground. Great for the ramp.
Buzz 7 (2002) and 8 (2003) used .25" plates for side “columns”, waterjetted for lightening. There was one of these on each side of the robot, and each was connected by extrusion. Each “column” had a plate, wheels/chain, and another plate, all attached rigidly. This was nice beacues the wheels were always in line, but the robot could flex. This allows for a great deal of flexibility. Like Buzz 6, you can actually pick up a wheel on Buzz 8 and the other three will still be on the ground. It worked great with the ramp, all 4 wheels were almost always on the ground.
Buzz 9 (2004) was an improvement on this design. We actually used .024 (?) sheet aluminum and High Density Polycarb (same as in our gearbox). The polycarb were the outer walls, replacing a sheet of aluminum. The inner sheet of aluminum was replaced with the sheet aluminum with flanges all around. Motor mounts were all sheet aluminum, too. Our motor pan that held all 4 motors only weighed I think a pound or so. Extrusion was still used to connect each side column, but next year I think they are using thinwall tube, which will cut down on weight even more.
Buzz9’s drivetrain, with the motors, wheels, chain, and multi speed gearboxes weighed in at only about 30 something lbs. (no battery or electronics yet, though)
I’ll toss in a vote for plywood, not as the best all around material, but certainly as the least recognized.
Aside from being cheap, easy to manufacture, extremely forgiving yet rigid and easy to replace, it can be very aesthetically pleasing.
A concern though is that a Wooden frame can ‘get in the way’, since it is going to probably be bulkier and in larger pieces then anything else. You just have to get out of the mentality of using the frame as a place to bolt things and think of it more as a subsystem all it’s self that has to be integrated with the others. Once you do you have something that looks more like a car (in the sense that it’s a single machine and not a collection of machines) and less like a Frankenstein monster (for lack of a better term).
Yes, I can already hear the ‘form follows function’ crowd, but hey… I like good Nordic plywood. Theres just something about a bot with a real form instead of these extruded boxes with lexan panels. A properly done wooden frame has elegance.
-Andy A.