Chassis Material/Construction
 

This is my effort to make a meaningful thread.

I am interested in what all the teams use to make their chassis. We have always used Bosch extrusion and will be using it again next season. What do you use and what are the pros and cons of different materials?

All steel for us. We had a welded steel frame this year and it worked very well for us. It weighted a ton, and probably limited our design, but it was strong, cheap, and easy to work with. We have used aluminum channel and tubing before (2001 and our off-season OCCRA competition), but we like steel better, and we can get it fast and cheap locally.

/me <3 extruded aluminum

very useful when you design and build the chassis, then realize it sucks, and redesign it and rebuild it, then realize it sucks...

We don't use any of that we, use 1/4 Aluminium plating with alot of holes in it. Makes for a very rugged robot.

Hmm...I think we use 1"x1.5" aluminum rectangular tubing. Not too sure on the dimensions. It's sturdy. Uhh...and it's sturdy.

Extrusion
 

The past couple years all we've used is different assortments of extrusion....This year we used more "aluminium tubing"(still extrusion?) because of weight.

:D

Example:
http://www.chiefdelphi.com/forums/at...=&postid=13472

We used 1/4" aluminum plate with 1/4" aluminum angle underneath for sturdiness. We also have a 1/4" aluminum angle V-cut in the front of our robot for handling goals. It's sad though - it's way too strong. Our engineer used it as a trampoline after he made it until his ankles hurt, but now we've cut too many holes in it for it to be used that way again.

Next year, bring on the extrusion and tubing! Let's go for a frame, not a plate, woo!

Sounds about right, or at least something close. Don't forget our steel anti-bumpers. Moe found out about them to well this year, there are still traces of them finding out about our anti-bumpers. :) Ohh yeah... it's sturdy!

We've used aluminum angle , extrusion, and angle iron.
We stoped using the aluminum angle because our welding teacher retired and we have no idea how to mig or tig weld(tried it once the results were not pretty) so we switched to angle iron which was much easier to weld, but weighed a ton. This year we used 80/20 extrusion which was nice and modular but was heavy also.
So out of my expieriance the best framing material is some sort of aluminum structural material like box or angle that you weld together because you just can't get a stronger lighter frame that actually allows you to put other mechanisms for the other part of the game on the robot.

This past year, we used 30mm x 30mm Boasch aluminum extrusion. It's sturdy, it connects well and we get a discount on it! ;)

- Katie

We always go by are moto ( Wood is good , Steal is real , and plastics fantastic ) just to share a little humor with you guy !:D

We used Bosch, because the team welder graduated last year.

It's great stuff to use, you can build a bot in no time, and disassemble it easily... but it adds unneeded weight. You could probabaly use 2 bars of aluminum tube for every 1 Bosch, and still have it weigh less and be just as strong.

But, hey, it worked great for us, so I'm not complaining.


Heh, it'd be sweet if someone built their bot outta polycarb. That'd be rather fragile tho. Just get some nice 3/4" thick polycarb :P

The bosch aluminum extrusions are not much heavier than the same size square tube with an average wall thickness. The extrusions are great for changing design, quickly adding mechanisms, and moving pieces without drilling. It's a snap to build and makes the whole project more modular. It is incredibly strong too. Also, its only a couple of bucks more than sq. tube.

The only downside is the cost of hardware. Those little brass alloy T-nuts are like 50 cents apiece. There's also the wierd metric hardware that's a little more money and harder to get then American hardware. The joiner plates are just a rip off so we make our own.

For those of you who voted wood, can we see some pics?

Somebody did. In 2001 (I think Adam knows this story better than I) they only used Lexan as a building material. They made 1/4" lexan angle, lexan sidepanels, and everything like that. No structural steel or aluminum at all.

It was pretty cool looking :)

EDIT:

Forgot to mention who it was! It was team 401. We were next to them in the pits at VCU, so I remember them lifting up lexan parts of their robot I could see through while we worked.

Yeah, but in 2001, you could get away with that. The structural concerns were not as great when you knew you weren't going to be in contact with opposing bots.

We noticed some NASA teams that pre-made connectors (like tinker toy ends) that hold tubing at different angles in the off season. THe keys here is build your 'proto-type' out of BOSCH then make the final out of tube by quickly rebuilding straight tube sections fitted into the pre-made connectors and giving it a little weld, which is much faster than making the custom ends on each piece when time is an issue. We will probably do this for 2003.

Bosch is great stuff, it just weighs alot, we did find we could 'remove' some excess material from sides we weren't attaching to for weight savings and it still was pretty strong stuff.
30x30mm

Love that Lexan
 

We've been using polycarbonate for several years now - I don't think anyone would accuse us of being fragile. This year our front frame was aluminum tubing and center pan was aluminum sheet, but most of the rest of the chassis (including the gearbox housings) were Lexan. It's easy to machine and assemble - it taps very easily for individual brackets and we use self tapping drywall screws for general assembly. A couple lessons learned - grease the screws and don't use locktite - it will shatter the laminate when it heats and cures. A key thing to remember in battle is that low spring rate materials will absorb impact energy better than stiff materials and lexan does a great job.

wheelman already said what we use


Badjokeguy

God Bless 80-20! SEE IT HERE! We usually go for the 1"x1" extruded 80-20 with 1/4 inch aluminum plate for the body. And also some 2"X 2" as well.

see example here and here

Yeah, we got some free samples of that stuff.

Could you explain a little about the "castors and one wheel on each side of your robot thing" I see in the picture?

Too heavy
 

I represent team 66. We build the sturdiest drive chassies i've ever seen, and can rarely be beaten. It is a little know fact that our robot for this last year was actually meant to handle balls. we only had one problem, a 95 lb drive chassy. We are big fans of the 1" extrusion but in my pit scouting for the last few years i have noticed something, The robots built for first don;t have enough power to bend 1" extrusion with any kind of blow.

I beleive that 20 mm extrusion, very light by comparison to its big brothers, has more than enough strength for our purposes.

As for polymers in construction, i haven;t seen many good examples of structural framing comming from it but have seen it in many good low impact uses (33's ball carrier a prime example. But after seeing the plastic bot of, i believe, 49 fall over at grand rapids last year and loose its arm, i have been weary of plastics use for robots.

Simple, pneumatically controlled drive systems. One primary drive, and one secondary drive. The pneumatic wheels are the drive wheels hence 4 of them, two drive each configuration. The castors are just there for balance. It is a thing of beauty, no need to have a wide turning radius. We just switch drive systems and drive in a 90 degree angle from the original heading. It all worked with our I.D.A.N. System described below.

"A mini press release if you will:

The 2002 Robot

The Watertown High School Sie-H2O-Bots have created the 2002 PAL (Professionally Automated Landrover) to be a combination of simplicity and robustness. The machine uses a total of eight motors to function. These motors include three Bosch drill motors with planetary gear transmissions, one Fischer-Price motor with a custom built planetary gear transmission, two power window drive motors, one air compressor with 120 psi capacity, and one small servo motor. The final product is a durable, fast robot with good maneuverability.

The robot consists of two operating systems controlled via remote control through a computer-generated program. The two systems control the locomotion of the robot as well as a grasping system to capture and release goals. These two systems will allow the team to score points on the field by maneuvering the goals into different positions of the field.

PAL 2002 utilizes a 4-wheel drive system. The primary drive system consists of two wheels located on the east and west sides of the robot. These propel it forward and backward with tank style steering via two flight sticks in the driver’s hands. Speed is achieved with the click of a button, which activates two small air cylinders, shifting the drill motor drives from low to high range and vice versa.

The secondary drive system wheels are located on the north and south side of the robot. They are engaged when the primary drive wheels are raised off the floor and the secondary drive system is lowered. In this position, the robot moves from side to side. The tank-style steering drives are toggled by the student driver who, at his or her discretion, regulates the speed, power, and direction they deem necessary. During driver training, the ability of the robot to rotate around the goals proved to be a valuable asset. It enabled the robot under strong power to slip out of normally pinned positions with other ambitious robots.

A pneumatic system consisting of an air pump, storage tanks, regulators, valves, flow controls, and actuator cylinders is used to give the driver the luxury of switching drives instantly at the squeeze of a trigger.

The grasping systems consists of two “fork plates” that are located on the north and south side of the robot. They are ¼” aluminum plate shaped like a fork. The controls are designed to deport the fork arms by raising them vertical to horizontal from the profile of the robot, like short wings. When driven into the goal structures, the arms will automatically grab and hook the goal. The second driver controls each fork arm independently with a small control box at the driver station. Lowering the arms and driving the robot away releases the goal.

The team’s very ambitious electrical team has developed sophisticated controls, wiring, and programming to navigate the machine. The navigational system compliments the robot design very well. Important symbiotic relationships continue to develop between the electrical and mechanical systems as well as between the drivers and driver feedback systems.

The electrical team of students and engineers has created a system that would enable independent control of the machine by a visually impaired driver. Code named I.D.A.N. (Intelligent Detection, Analysis and Navigation), the system allows the robot to provide audio feedback to a laptop computer.

The cornerstone of this system is a tiny magnetic sensor that will read the earth’s magnetic field. The signal it sends out will identify the direction the robot is facing. This information also establishes the robot’s location within the five zones of the playing field. An optical switch receives a signal every time the robot moves over a line of white tape bordering each zone.

The robot has been installed with optical switches on servomotors, which allow it to “scan” for the goals and correct its path automatically. The optical switches respond to the retro-reflective properties of the tape on each goal. A pressure sensor inside the robot arms will determine that the goal is secure. The Sie-H2O-Bot team looks forward to gaining extremely valuable experience with this very sophisticated system as the season progresses.


Our experimental "Blind Drive" system won us the leadership in controls award in NYC as well."

wood all the way. why, because its inexpensive and does the job. We were attacked left and right this year, slamming into everything and the wood did not bugde. Our team loves it.

We used 1.5" Steel angle this year, because some genius thought that we would really need the extra strength. In reality our frame weighed a TON more than it should have. In the past we have used 1.5" aluminum angle, and it worked great.

bosch is good bwa-hahaha

80/20 is better (And no its not because our main sponsor sells over a million dollars of it a year and gives it to use for free)

We've been all across the board.

96. ALL WOOD. Even the wheels!
97. Wood/Steel frame Hybrid. This bot Rocked! 2nd place in NJ
98. All Steel frame, all alumin upper chassis. 2nd in NJ again
99. again, all steel, and alumnin upper chassis
00. Aluminin Frame. Actually, the whole bot was aluminin
01. Aluminin / Bosch Hybrid
02. All Bosch. She was a tad heavy, but we have never had a bot that wasn't within a few ounces of the limit.

Another funny correlation. 96 and 02 had the same drive train, two wheels.
all the other years had skid steer. (Think like a tank)

We like steel. Our two most successful robots have hade a steel frame. We used aluminum, too, for our mast in 2000, but 2002 was all steel. It was ridiculously heavy, but for our simple but effective design, it was perfect. We took a heavy beating, but the only damage was superficial damage to our Lexan paneling.

We've done wood and aluminum, too. Our 1998, 2001, and OCCRA bots are all wood/aluminum hybrids. We make an aluminum frame and put in a wood base and side walls.

When I heard chassis I thought it was a computer chassis or such.

DUH!

Anyway, aluminum tube, it's stronger and lightweight.

Chassis
 

Some of you said that polycarb was brittle and or shatterd easily, those people are confuseing polycarbonate(aka lexan) with acrylic. Acrylic is very brittle, which was best demonstrated at the seatle regional when a team had a scoop made out of acrylic and the opposing alliance threw a ball into play, and it hit the scoop, the scoop shattered. Polycarb on the other hand is extremly tough in fact it is used instead of plate glass in prisons and things of that nature. I saw a demo of polycarb on TV where they invited members of the LA SWAT team to try and break the stuff. The SWAT team tried to break it with sledges, axes, pipes, and crowbars and failed miserably. So they came back with their automatic weapons and fired on the stuff with MP5 sub-mchine guns (NO JOKE) and the polycarb stopped every bulleto a full 30-round mag!! So polycarb(aka lexan) is extremely tough and has no problem holding up to any and all FIRST applications.

My team used extruded aluminum for our base in the form of a "c" shaped structure which was temporaily bolted together for testing and then was TIG welded at the end of testing. Then we built up from there with alum. angle. Then a plywood base to mount ball gathering mechanism and electronics. Why did we use plywood you may ask, because it as avalible and it is so much easier to work with then metal will ever be. Even though it is ugly as can be. On top of the plywood we used alum angle for the ball hopper which filled out the maximum allowed space.

Re: Chassis
 

Unless you effect it chemically. In 2001 my HS team had forklifts made out of 1/4" lexan. We spray-painted them so that the drivers could easily see them from the booth. Late in the day at Long Island, we had a minor collision with 263 (they blasted right into us coming into the endzone) and the forklifts shattered.
Near as we can figure, the Lexan was weakened by the spray paint.

Moral of the story:
Don't paint Lexan. It can weaken it greatly.

That is a very good point to not paint lexan. Generally plastics dose not like to be sprayed with solvents(which spray paint is). They tend to weaken them by eating little holes in them. Thus, as you know, they become weak and brittle. 1/4" Lexan is about the weakest lexan you can find. The lexan used in the demo was most likly of 3/4" to 1" thick lexan.

Re: Re: Chassis
 

Are you sure this was Lexan? I have never heard of Lexan shattering, but acrylic would do exactly what you say. Certainly spray painting could have surface effects but by the molecular nature of polycarbonate I don't see how it could shatter, even if the surfaces are eaten away a little.

First of all I don't see why you'd ever want to spray paint lexan as it's crystal clearness is beautiful as it is. Perhaps a custom airbrush job but I'll save that topic for another thread.

As for the lexan shattering, this is completely reasonable given the circumstances. The spraypaint acts as a solvent and attacks the lexan making it brittle. Pactra and Parma both make paints safe for lexan. They can be found at your local hobby shop. Here's the link for the Parma paint http://www.parmapse.com/faskolor.asp

Re: Re: Re: Chassis
 

Positive. It was the real stuff. It took quite the hit to break it, but still.

We painted our Lexan panels last year. That's how we got the black color. We dented it a little, but it never broke (and it took some big hits, too).

The lexan that was spray painted and shattered was 1/4" thick this is important. Lets say that the paint eat away at the 1/16" deep(very conservative estimate) on all painted sides that leaves 1/8" of untainted material left to hold up to an impact. since the imapct was on there goal grabber forklift and it most likly was nt supported except on the end and it was probably over 10" long that leaves an 1/8" thick 10" long piece of unsupported lexan collideing on edge with an unforgiving piece of metal(most likly). Shattering sounds like the logical solution.

If you want to make your forklift visible I would have used a bright shinging tape. Like a neon yellow tape or what ever would match your bots color scheme.

Here is a pretty good website w/ Metric and English properties of polycarbonate (aka lexan).

http://www.matweb.com/SpecificMateri...&group=General

This was the solution we came up with for Nationals. :D

Titanium?
 

We'd love to use all Ti plate and tube, but C & A might balk at the materials bill! So instead we've used the 1.5 x 1.5 extrusion in the past. There is a considerable weight penalty once you add all the hardware to put the frames together. I like how the Huskie Brigade designed this years bot. Using the shape of the Huskie as the primary structure. I also likes the Killer Bees chasis. Standing .156 plate on edge, connecting the plate with tube is strong and light. And as their leader says "some chasis flex helps keep the wheels on the floor.." Working with sheetmatal most of the time, I appreciate Wildstang's bot as work of art. It is amazing how strong thin sheets of aluminum become once you start putting bends and beads in them. The benfit of the extrusion is the rapid build and ease of maintenance once the bot is together. The trick now, is to use the modular concept for ease of assembly and modification, making the components durable enough for the application, but light as possible....I still want an all Ti bot....:D

The only sheet metal chasis?
 

.09" Sheet metal, oh yeah.

Aluminum Extrusion in Kit
 

We plan to use some of the aluminum extrusion in the kit this year. Has anyone found a marking on the box extrusion or a spec for the exact alloy of aluminum used. We need this for a compatible weld material.
Thanks

We (60) use 1"x2" & 2"x2" 1/8 wall 6061 Aluminum tubing
(good weld-ability / good working) with a lexsan floor pan/side panels for the main frame
alum tubing / plate for components
6061--- yield strength is 40 ksi hardness is 95 brinell
melting range is 1080f to 1205f
also heat treatable (let cool Slowly or crystallizing may occur)
SEE statement below

Shhhhh... everyone keep this a secret, we use sheet metal .090 thick! But i'm not gonna tell you how we do it!
We have wanted to build a full sheet metal frame using 6061-t4 aluminum. We felt we could achieve a better strength to weight ratio.

I'm really interested in seeing what sorts of results you all have with the sheet metal.

We're using .19" sheet metal for our frame, with some beefier stuff mixed in here and there. I was a little scared of going thinner than that. We'll see how it shapes up in a few weeks, I guess.

Good luck.

Sheet metal is what the body of your automobile is made of. By golly I think what your talking about is honest-to-goodness 3/16" PLATE. That will do just dandy for any robot is my shop.

Nothing against extruded aluminum, cause i love it to death, except for the fact that it is just too heavy, so i think we are going to eventually go with the aluminum tubing, either round or rectangle. But i do know one thing for sure, we dont have the weight to spare this year..:(

we are using aluminum 2x4 tubing that came in the kit. it works well and is strong but we cant weld a lot of disimilar metals on it.

We're going to use 3/4" square tubing for our bot this year. We're making a steel prototype, but the final version will probably be aluminum.

Re: Too heavy
 

20mm extrusion is something that we've looked into too, and I think that's definitely a possibility to reduce weight, though rough calculations would show the moment of intertia would drop to about HALF that of 1" 80-20 just by reducing the overall width and height (and presumably weight) to roughly 80% (20 mm / 25.4 mm/in) . That's the one reason that we haven't made that switch. Has 20 mm been used by your team in the past?

To keep with the thread:

In the past two years we're always using 80/20, 1010 (1" x 1")... and here's why:

The moment of inertia of 80/20 1010, which is 1" x 1", is .04413 in^4
The moment of interia of 1" x 1" x 1/8 thick box is 0.0570 in^4

The weight of 80/20 1010 is 0.495 lbs / ft
The weight of 1" x 1" x 1/8 aluminum box is 0.511 lbs / ft

So.. for those of you trying to save weight, look again!

Check it out at:
http://www.8020.net/pdf/Fractional/0...%20(31-62).pdf

Obviously though, it's more expensive than box aluminum. We were purchasing it at around $2.50 a foot. Box aluminum is about $1.50 a foot off of www.onlinemetals.com

People tend to make assumptions... crunch some numbers and you'll be surprised what you find!

In addition, the ability to actually CHANGE your frame around makes 80-20 great stuff. You can buy a 100 pack of t-nuts for $.08 each and go to town. Where 80-20 makes all their money is on those brackets and corner squares at $18 each. We make our own and come out just fine.

Matt

Re: Too heavy
 

Though the 8020 extrusion itself may be lighter per foot than box aluminum, don't forget to factor in the weight of the additional fasteners and joining plates required to make it all stay together. If a team has access to aluminum welding equipment, it's probably lighter to weld a frame together from box aluminum than to make it from extrusion -- depending on its design, somewhat.

Re: Too heavy
 

Let's see.

If you're using say 25 feet of 1" 80-20 for your frame, you'll save about .4 lbs over box.

40 1/4-20 bolts at 5/8" long, 8 of those corner fasteners (about .025 lbs each) and prolly about a foot and a half of 1" x .125" angle (at .2742 lbs / ft) gives you fasterner weight total of about .752 lbs...

<math skipped, have faith in my algebra>

So using 1" 80/20 for your frame is about 3.1% heavier than box aluminum, fasteners included. (13.17 lbs vs. 12.78 lbs)

Absolutely worth it IMHO.