Has any team or anybody made a 80% - 100% lexan bot?
 

I'm looking for pictures and any details on a robot that is made of lexan or any other material then metal. It goes with all these posts.

**I'd like to add a note this is for my senior project and it will be done before the start of the season and i will be doing extensive testing on the durability of the materials chosen, since we will be going to 3 competitions this year.

6 wheel bot

Belt Drive

Drive the 6" wheels

thanks!

pictures if possible

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I believe 1038 had a frame made of lexan in 2003.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Here's a picture of it...it was acrylic and was apparently not used because of "design flaws."
http://www.chiefdelphi.com/forums/sh...threadid=17366
Hope this helps.

-Steve

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

190 made their 2003 chassis out of lexan, it was SICK! they had no problems until battlecry when the lexan split right down the middle of the robot


that was an easy 6-7 events before they had a fatigue problem.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

SPAM team 180 has mad robots, even the gear boxes were out of lexan i believe. I belive this one below was called lexy.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

One reason i am against using lexan as the chassis... it may break. example was given by greg...

Edit- andrew, spam is a great team. and yes they have made 3 robots out of lexan. none of the robot broke during the competition. the past three years (2002, 2003, and 2004) they used aluminum as their chassis. for a game like we had in 2003 (Stack Attack) i wouldnt build a robot using lexan. but still you never know, you might be able to come up with something very solid.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Any material can break.
Engineering is about designing such that the materials used can withstand the forces applied.

It's true, a robot chassis made out of graham crackers (my default, "weak material" for examples) probably wouldn't hold up. However: lexan, aluminum, steel are all TOTALLY doable.

Lexan's main advantage is it bends quite a bit before exceeding the elastic point. However, this is also a disadvantage when it comes to chassis design. Aluminum is much more rigid, and rigidity is important for some chassis applications.

Enough rambling... my point is:
Lexan is a totally viable chassis material, and I'd be more worried about it bending and throwing a chain or something than worried about it breaking.

John

edit:
Despite it's "bendability" (there's a fun fake word) Lexan can STILL be used effectively. Check out the above picture of 180 and see how they got around it. Note the cross bracing and box stucture (very high rigidity). Good stuff.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I agree. Plus Lexan is expensive. I'm on 95, and we hardly spend any money on our 'bots. We use 9-layer baltic plywood becuase i can absorb damage much more easily. Plus it's really easy to mount things to. But Lexan does look pretty cool.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I don't have any numbers off the top of my head, but I'm pretty sure lexan is horrible in most strength(tensile strength, etc)/weight ratios compared with aluminum. I'd venture to say a good quality plywood will even exceed polycarbonate.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I would tend to agree. It certainly has terrible performace/cost ratio. We only have about 900 extra dollars to spend on our bot every year, so every dollar counts.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Really? I've always been told that aluminum and lexan have almost identical strength/weight ratios. However, as it has been stated before, lexan is much more springy than aluminum, and will bend and flex (which led to 190's 2k3 bot throwing lots of chains).

Also, I agree that lexan is much more expensive than aluminum, and 190 would probably not use it if we didn't get it donated every year. In fact, in 2003, the lexan that was donated to us was Hyzod AR, which is a pain to work with due to its abrasion resistant coating, and normally costs $300-$500 for a 4'x4' sheet (about twice what normal lexan costs).

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Max,
What you posted doesn't "mesh" with what I thought to be true. Can you go to www.matweb.com and get the actual values, and report back your results?

I'd do it, but I'm working on something else right now.

Can anyone out there do this for me? I'd really appreciate it.

Maybe a comparison between 5052 H34 aluminum or 6061 aluminum, and whatever common grade of Polycarb McMaster-Carr sells?
That would be awesome.

Real enginerding -- you betcha!
Thanks,
John

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

is this what you wanted John?...


http://www.matweb.com/search/Specifi...snum=MA5052H34 ... thats for 5052 H34 Aluminum...


here are few examples of 6061 Aluminum...

http://www.matweb.com/search/Specifi...ssnum=MA6061AO

http://www.matweb.com/search/Specifi...assnum=MA6061A

here is an example of lexan....

GE Plastics LEXAN EM1210 Polycarbonate
http://www.matweb.com/search/Specifi...snum=PGE8NA117

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I was already on it, and would have had it posted before you, John, but Firefox crashed :(

I used ultimate tensile strength as other websites have suggested it is the standard for strength-to-weight calculations. I would have thought yield strength is more appropriate, but I can't find that data for Lexan.

GE Lexan (clear, no glass) ---72 MPa -----1.2 g/cm3----- ratio 60
Aluminum 6061-T6 ---------310 MPa -----2.7 g/cm3 ---ratio 114

for comparison:

very strong titanium ------- 320


steels have an incredible range of like 40-250 but as far as I can tell (I'm not sure what are the most common types), structural steel is in the 80-110 range.

Amazingly enough, a high quality piece of wood (European ash, is good, apparently) can have a ratio as high as 320! in the direction of the grain though it is a mere 12 perpendicular to the grain.

I'm trying to find some good data on plywood, but it looks to be approximately equal to PC (but of course it is bidirectional, unlike regular wood.)



carbon fiber ----------------3200

kevlar----------------------2100

I know that what is generally considered the strongest material ever created was carbon nanotube fiber (spun by some of my dad's former co-workers :)) but that is using some other measurement of strength (I believe Young's modulus).

Note that the properties of these extremely high tensile strength fibers aren't simply comparable with steel and aluminum. You can't build a robot 20 times lighter out of carbon fiber.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Cool!
Thanks a lot. It is always nice to see someone back up their argument with numbers. Props to you, AND to Arefin for taking the time to do some research (Which is very important when doing design and analysis.)

You guys rock,
John

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Team 104 has used polycarbonate for a frame covering the last 3 years. We use 1/8" and 3/16" 6061-T6011 aluminum 1" angle for the frame joined with steel pop-rivets and backup washers. The polycarbonate is held on with 1" velcro. Mcmaster Carr sells velcro with a very strong contact adhesive. We have a sign shop make our decals to be applied on the inside. The inside of each panel is then painted. Our decals and paint can't scrape off. Note- make sure the paint is for lex an. Most paints do not stick. We have not experienced any frame damage or panel damage.
Polycarbonate is expensive. As was noted in another post, birch furniture grade plywood is very strong and light. To take it up another notch in rigidity and strength, Try laminating 5mm, 3/16 or 1/4" plywood with 1 or 2 layers of 4 oz. s2 fiberglass and epoxy. It's an excellent structural material and is fairly cheap. With our budget constraints this year we may have to use it.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Yes, but other aluminums don't fare as well. 5052 aluminum, for example, has ratios between 70 and 100. Other aluminums range from a ratio of 17 to a ratio of 237.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Yes, but the lexan motors kept on melting.... :ahh:

MrToast ;)

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

6061 is definitley the most commonly available (and probably one of the cheapest) types of aluminum used structurally. Most of the aluminum extrusion kits, and most of the tubing/angle/channel found on FIRST robots is 6061.

Additionally, Polycarbonate varies (you'd have to go to some other brand than Lexan) and glass filled PCs have ratios around about 80. I'm pretty sure glass filled PC is too hard and brittle for most framing use.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

And just because the use of this by teams that have plenty of metal machining capabilities annoys me:

pipe type PVC ------ ratio 31

80% - 100% lexan bot?
 

Team 346 (Richmond) made one in 2001, I believe it was. There were a couple of pieces of aluminum angle connecting the Hyzod platform to the side panels. Each side was doubled up and contained a chain driving 3 wheels. It looked very much like one of those WWI tanks, as the front was intended to crawl over the 4x4 in the middle of the playing field. The polycarb was appx. 3/8" if I recall. I don't have pictures, but perhaps someone from 346 does. The frame held up well, although the bot was pretty light.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

does anyone from 401 or any team know anything about this bot?

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

what exactly annoys you?

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Heh. Perhaps that was a bad choice of words, but, in general, it is annoying when a simple design choice could have significantly improved the end product.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

personally, i believe that using ENC (the grey PVC) is good design choice. its light, flexible, strong (enough), cheap, and above all, easy to work with.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

empahses added

Re: Has any team or anybody made a 80% - 100% lexan bot? Yes, I have!
 

MY ROOKIE YEAR ROBOT!

Yes that is Sexy Lexy in her KSC glory. :D At Epcot we added a turtle shell to her chassis for additional protection and were attempting to install a hanging mechanism. Her gearboxes were lexan as well as the following years robot 3-bits (3-bits bad grrrr).

As many has stated it is expensive. Polycarbonate sheet is used as bulletproof glass. We got some donations from a local hurricane shutter manufacturer that year. However, an all lexan bot also sets you apart from the rest as some of us were remembered as the dudes with the clear robot. Before I digress any further, lexan is easy to work with basic machine tools you could get at home depot, loews or any equivalent respectable hardware store. That year if you looked at our pit, that's pretty much what we had at our shop. Belt sander, band saw, couple drill presses...... we've come along way.

When designing, you should also consider not only how will you manufacture it, ease of repair, but what materials. Obviously you don't want a large force extended out on let's say an arm that's just from what you made it out of not to mention whatever you intend to manipulate like this past year a ball.

Oh paint sticking... somehow we managed to get some neon green on lexy when we climbed on top of Swamp Thing somehow (ask Ares.. he was driving ;-)) almost 10 points but we were touching the ramp so only 5.

Thanks for the trip down amnesia lane. :ahh:

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

i look at it like this: i would much rather repair/replace an arm thats made from lengths of PVC tubing than an arm that is made from custom machined alum. at a competition. plus all the weight and/or money saved by using PVC can be put somewhere else, such as a drive train or electronic components.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

another good part about pvc arms is that they wont dent or bend out of shape like some aluminum arms. And if you are worried about it shattering.. how easy is it to cut out the broken part, cut a new piece to size, and put it in with 2 couplers and some glue! woohoo go pvc!

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Tom beat me to it, but this fact was a driving force behind our decision to use PVC for a telescoping arm to reach the bar last year. We knew we'd be subject to punishment from teams cause we were reaching from the ground, and we knew there was a chance for the arm to get bent, so we chose PVC for it flexibility. We had our arm literally wrapped around a pole a couple of times, and it was fine. I saw a team at Lone Star have a metal arm wrapped around a pole, and it was ugly.

So, in summary, PVC definitely has its uses, and you just need to consider what you're designing for, like any other engineering choice.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Max, you must hate Beatty, then. Each of their 4 national championship robots have used PVC in an integral way, along with their custom machined metal parts.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Though I have not had the pleasure of seeing one of 71's robots, from the pictures I have seen, I have great respect for their designs. They exhibit the kind of engineering efficiency few other teams have.

I am not entirely opposed to using any particular material, I'm just pointing out commonly misused materials.

Of course, as I have stated in several threads, material choice is more than simply the best performance for your weight or even for your money but the best performance for your money, weight, and time. You may find a piece of PVC that happens to have a very efficient shape and creating a shape out of a better material with the better efficiency would take too much time or money. I'm only concerned with what I would consider blatant errors like an entire robot out of Lexan.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

We made an all Lean chassis on Team 49 back in 2001.

http://www.chiefdelphi.com/forums/pi...&quiet=Verbose

We had some problems with a lack of rigidity.

Matt B

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Max, please be more careful with your choice of words. It's not the materials that you use, but how you use them that matters. As others have mentioned, you need to be aware of your specific needs and of the strengths and weaknesses of any material you might use. Once all of these considerations have been made, then you can choose the best material for your situation.

To say categorically that making a robot from lexan is a blatant error makes you sound narrow-minded at best and ignorant at worst. SPAM's 1999 and 2000 robots were nearly entirely made from lexan and no one who saw them or played against them would doubt their ability or robustness. Also, SPAM used lexan for vital structural pieces on their 2001, 2002, and 2003 robots with complete success.

I'm sure, as with any other material, there are many teams who have use it successfully and many who have not. I'd say it's similar to how some people refuse to use wood on their robots, yet teams like 173 and 61 use it masterfully. Know your material, know your purpose, and you won't go wrong.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Since this thread has turned to a choice of materials discussion, I would like to point out that in the past 3 years I have noticed a increase in rough play in the game. In 2004 we took several high impact hits. We fortunately survived them with no damage. I would suggest that all teams look at the materials and design with the goal of surviving high speed point impacts. More and more teams are using multiple motor trans and the power and speed is increasing. Plan for it or you'll find you self in the pits making emergency repairs. What worked in the past may not work as well for 2005.
First has opened up the allowed materials. Evaluate the choices and use them.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Seems like people on CD are just out looking for something to be offended by. If there is anyone here who can't find significant design errors on every single robot in FIRST, they obviously don't know much about engineering or building robots.

Additionally, I didn't say categorically that the use of a material is bad, just that certain materials are commonly used incorrectly.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Care to point out a design error in Team 60 and 71's robots in 2002?

And those were just the two that first jumped to mind.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

You know the argument is getting a bit ridiculous when people start using very obscure questions as points...

Nevertheless, if you insist, I will try. I have never seen either of those robots. If you can provide me with a couple of good quality pictures, I might be able to give you an answer.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I found a couple pictures, don't know if its what you are looking for.
Team 60 - http://www.firstrobotics.net/02galle.../060-1_jpg.htm
Team 71 - http://www.firstrobotics.net/02galle.../071-1_jpg.htm

Try searching soap108.com for videos, I think they have some.

I tend to agree that there will be a few flaws here and there in all bots, but I don't think FIRST meant us to build a perfect bot. Every bot is built to do a certain thing and accomplish a certain aspect of a game.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Another good example of using plastic as a constructive material is 1999 TKO robot from 45.

Polycarbonate, in this case, was an excellent material choice. It was better than steel or aluminum. Anyone want to guess why?

Andy B.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Because it's not too good an idea to have all the weight steel or aluminum would bring, 8 feet up in the air?

And Max, I didn't think it was an obscure question at all. Those two robots are widely acclaimed as among the best ever built by FIRST teams, and all who saw them in action would probably agree that they dont have any significant design flaws.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

It is clear and wouldn't block the drivers view?

In 99, when the playing field was only 24' x 24' I don't know how much more you would be able to see, but that's my guess as I am sure an arm made of aluminum or steel could be equally strong for the same weight.

The only other benefit I can think of is thermal and electrical conductivity (or lack thereof.)

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Well if I remember correctly--
The tkats used that mean arm as a "stiffarm" to prevent teams from getting onto the puck. Perhaps they wanted a "flexy" arm that would give a little bit when it was under "stress". This would protect their gearboxes from damage.

Best guess...

John

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

mmm, yes, good call.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Please define "design errors".

If a particular design meets requirements, then by the definition most professionals use, it is correct. If it doesn't meet requirements then it is not. Requirements should NOT be general, like "it won't break". They need to be specific as in "won't break when subjected to a load of 100N in a particular direction". The more numbers the better.

We generally develop a list of requirements for our robot each year. It will include things like "move across the field at 7 ft/s" or "lift 45 lbs of boxes to a height of 3ft in 3 seconds or less". If it meets the requirements (including cost, weight, and time to fabricate) then it is a CORRECT design. That isn't to say it is the BEST design. There will always be room for improvement, but you can spend your life analyzing to get the best result only to find when you look up that it is now next year and there is a new game.

We tell our students "In this game, if you meet your requirements, you win. BEFORE you ever take the field." After that everything else is gravy. (BTW you will win on the field a fair amount of the time as well if you have set your requirements correctly)

We started doing this systematically in 1999. I can't think of a robot since then that hasn't been a "winner", though some have done better in competition than others.

In saying that every FIRST robot has significant "design errors" (whatever they are by your definition) you are impugning the skills of a fair number of technical people who do this sort of thing for a living. Kind of like an apprentice telling a master he's doing it wrong. So don't be too upset if people take offense because, quite frankly, you have just been offensive.

But you're young and foolish (all of 17 is it?) so we won't hold it against you.

ChrisH

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Correct. Not only did this design protect gearboxes from damage, but the arm could withstand a significant deflection and then spring back into its original straightness. I remember a few times when the arm's polycarbonate box structure would buckle and bend at a 90 degree angle, and then it would spring back after the load was removed. Sure, there was some damage to the arm, but it did not fracture and we could easily repair it.



Many plastics have great elasticity, while most metals do not. Shown above and linked here is a stress strain curve for a high grade polycarbonate. As stress begins (lower left corner of the graph), the material goes through its elastic stage. Until the stress hits the material's Yield Point, the material can bounce back to its original structure. As the strain increases, the yield point is passes and the material is in the "plastic region". This is the area where you see the material being bent, and then maintaining that bent shape (not springing back to original form). Then, at the end, to the right is the Ultimate Strength point, where the material fractures.

All materials have these stress/strain curves, just like all motors have torque/speed curves. The main difference between plastics and metals is the distance between the yield point and the ultimate breaking point. With metals, the distance is short. With plastics, it is much longer. Therefore, choosing plastic (Lexan, PVC, etc.) as a construction member for a FIRST robotics design is a good choice, since these members see much deflection at times.

Andy B.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I have great respect for all the people to commit their time to FIRST and I have respect for the work they accomplish. That is in no way mutually exclusive to these same people not doing perfect work and having "significant design errors" (would we even be talking about any other kind of design error?).

When I was talking about design errors, I was referring to different requirements then you were. Not the requirements that are set by teams for themselves (the best teams probably nail all of these requirements consistently), but the requirements of the job. The requirement is simple: make a robot that wins. If it was possible to make a more robust robot, or save enough weight to add an aditional useful mechanism, etc, then I don't think the design was "correct". (I'm not speaking about the more general design as it is very complex to analyze wether a ball herder is better than a ball carrier or wether a hanging mechanism is worth the weight, etc, etc.)

The only thing I have been saying is that a very common design mistake is a bad choice in materials. As Mr. Baker pointed out very nicely, and as I didn't and don't disagree with, certain materials do have unique properties that aren't encompassed by the single number I was using for analysis.

If I have offended anyone, I apologize, but nothing was meant to be offensive, and I hope I have explained my intentions to you. This thread has gone way off topic, so if you really wish to continue this discussion, perhaps do it in private.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

I probably posted this before but Lexan/Polycarbonate has a pretty cool effect to spot wear and tear. Take two polarizing lens and rotate them so that you can't see any light coming out of them. Now look at a clear light source (glass, lexan, polycarbonate) and at points where there is stress you should be able to see rainbows/something.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Team 1038 did use the Lexan pictured in this thread. It wasn't acrylic. We only had minimal damage - a chunk taken out of a side plate during the 2003 IRI when a very strong and fast team tried to remove us from the top of the ramp. We also used 80% Lexan in 2002 when we were team #144. There may be some pics in the image galleries from that season. That machine was great. We like polycarb because it is workable for our students and it has many close characteristics to 6061 Aluminum. We also get it donated by a couple of our sponsors, therefore very affordable! One of our students (CD username crispyc) did a Strength of Materials project while studying at Miami University. I'll see if he has any of his research around. Good luck with your project Alex. I'll PM you if I find Crispyc, or his project.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

A few points about Lexan that we've learned over the years:

1) All polycarbonate is not created equal. We have tried cheaper forms of polycarbonate and found the the GE LEXAN brand name is definitely stronger / more rugged than others. There are different varieties of GE LEXAN as well, but in general they are all better than other manufacturers.

- Also, please don't confuse Lexan or polycarbonate with acrylic. You might as well make your robot out of glass if you go that route.

2) We started using Lexan when it was an unlimited allowable material because it made very nice assemblies. It is easy to machine and it makes nice square corner joint assemblies - we drill pilot holes through the edges using 3/8 inch thick Lexan and use self tapping drywall screws. You need to use Lithium grease or the screws will shear while torquing (use the low torque setting on your cordless drill when installing them), and don't use locktite because it heats up, expands and cracks/delaminates the lexan.

3) An important point to understand when talking material choice is that for impact loading (like running into other robots or them running into you or your components) the imparted load is NOT INDEPENDANT of the material or construction of your robot. The kinetic energy input (1/2mv^2) is absorbed by the structure based on its spring rate; a very stiff structure will take a very high effective g-loading, where a soft structure will see a much lower load. So you could say for instance that aluminum is twice as strong as Lexan, but it the aluminum structure will see 10 g's and the lexan structure will only see 2 g's when they run into something, the lexan may be the better choice if you can tolerate the deflection. This is frequently the case with some mechanisms that don't require precision, and why PVC is a very good choice for them in many cases.

One other point about aluminum if you're making the comparison for a structure: 6061-T6 loses 2/3 of it's strength when welded. The Aluminum Association Handbook takes it from 35 ksi yield to 12 ksi yield in the heat affected zone (within 1 inch of the weld) so be careful.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

Funny, there haven't really been any references to plywood in this thread.
For my team's first 2 years we used 3/8" plywood. Though in 2002 we had this large steel "knee breaker" apparatus that was used to grab ahold of goals. In 2003, however, the only metal you could see on the robot was the angled alluminum, 1/4-20 bolts and lock nuts used to hold the chassis together. It was sweet.

Re: Has any team or anybody made a 80% - 100% lexan bot?
 

While that would probably work quite well, I would highly recommend that anyone using lexan first glue the pieces together using an unthickened methylene chloride solvent glue. You can get this from any plastics supplier. It is applied using an applicator bottle that has a needle tip and uses capillary action to flow between the pieces of lexan. The solvent breaks down the plastic's surface, allowing the pieces to chemically weld themselves together. Edge preparation prior to glue application is of utmost importance. Your final seam will never be better than your beginning edge, so you may need to use a mill to make a flat edge if you are gluing a cut side.

Once the edges are glued, you can drill and tap them (or use self tapping screws if you are feeling lucky), and they will never come apart.