Will plexi-glass work?
 

so anyway, my team gets this great idea to make our robot's frame completely out of plexiglass. With only little metal brackets. I do not think this will work. We are an am. team, and we have nothing done. We have a few small pieces of plexiglass and a few metal brackets. we have no wiring done, no drivetrain. A flawed design that basically will only move. Sooo.....my question is.....Can we basically bend over and kiss our chances of even getting this done goodbye? Any help would be appreciated! thanks

Mathew Smith
team 1352

Re: Will plexi-glass work?
 

plexi glass is heavy!! not only that, but in the competetion (guessing you've never been to one) there is ALOT of pushing a shoving and ramming into each other. If there was no support behind the plexi (like studs in a wall) it would most likely break. I dont know about you, but i wouldnt want to have to fix plexi in the pits. If you are really looking for an easy way out, try getting some reliable wood, or just using the frame they give.

Re: Will plexi-glass work?
 

This is not supposed to be mean, but, you have NO chance of surviving a match with plexiglass. It will crack and break and splinter into a million pieces when another robot just barely nudges it... Our team learned this the first match in 2001 @ NYC. Hence why we have lots of lexan on reserve now. Attached is a pic of the shattering (the other robot barely nudged us on the side)...

Re: Will plexi-glass work?
 

I'll throw this link in here so this thread doesn't turn out to be bad.

Critical and picky - here I go again

Even though i've not had much experience using Plexi-glass in robot operations, I've played with it enough to know that it will shatter and crack fairly easily. I also seem to remember a lot of threads in the past asking this exact same question, "Should we use plexi-glass or lexan" and the majority of the time most responses went, "Use lexan" for one reason or another.

Also, one thing i saw was people confusing the terms lexan(polycarbonate) and plexi-glass(acrylic). I just don't want this thread to turn into a "Let's argue about what its called thread".

This is not the end of the world for your robot. With the right support I think it will be just fine, but that's just my opinion.

Re: Will plexi-glass work?
 

Plexiglass is a tough thing to use for robot body. It does shatter and easily cracks when you drill into it. Lexan works better and is less prone to damage but weighs a ton, heavier than aluminum. No you are not out of the competition at this point. Just think about a little modification. Use some aluminum extrusion to frame out the same dimensions you already have and start bolting it together. Move things bit by bit over to the new frame and voila! a robot is born. If you can't get it done before ship, cut as much as you can now and ship all the parts in the container with the robot. You will have lot's of work at your first regional but you can get it done. Ask for help from other teams, they are required to help if they can. I know that one team at Great Lakes last year, came with a box of parts and built their robot at the regional. "Never give up, never surrender!!"

Re: Will plexi-glass work?
 

Good advice. One of the things that many people get confused with is the difference between acrylic and polycarbonate. Plexiglas is the best-known trade name for acrylic and Lexan* is the best-known trade names for polcarbonate.

Many people get these two materials confused. I hope that Mathew is saying plexiglas while his team is really using polycarbonate. Like Yan said, polycarbonate works well for many teams, but acrylic does not.

Mathew - are you sure it's plexiglas and not polycarbonate?

* btw, here is a related piece of trivia: Lexan was the first polycarbonate invented. Dan Fox mistakingly created it in 1963, as he was working at General Electric. GE had the patent on it for 17 years before another company could make it. Now there are other trade names, but Lexan is still the original. (I spent 4 co-op terms working for GE Plastics, making Lexan and Ultem.)

Also... a side note: the density of polycarbonate is 0.043 lb/in^3 while the density of aluminum is 0.098 lb/in^3.

Re: Will plexi-glass work?
 

I'm sure if they broke any pieces drilling them it probably is polycarbonate. Those materials are a pain in the but to use.
Actually they are trade-names which is why it gets so confusing. The trade names for polycarbonate are: Lexan, Hyzod, and Tuffak. The trade names for acrylic well according to my book there is only one trade name. It is plexi-glass. Go figure. Also I have heard bad stories about using loctite on plastic materials. I heard it actually weakens the materials. Anyone care to find out if this is true?
*hint* Want to see something cool. Take two polarizing filters and stack them one on top of the other. Turn them until you can't see any light coming out. Then point them at a opaque material like lexan. You would be able to see any of the stresses put on the material*end of hint*

Re: Will plexi-glass work?
 

thsi late in the season I recommed you use 3/8" plywood for the base and the 2x4 alum pieces that FIRST gave your for the sides.

we built a pratice robot like this in november with parts left over from last year. It only took us 3 one hour meetings, at the highschool, to put it together and get it running

Im certain you could do the same in one weekend.

Re: Will plexi-glass work?
 

Sorry to hear about your problems, but don't throw in the towel yet. It's easy to get overwhelmed, especially in your rookie year, with trying to do too much and seeing alot of things fail. You still have over a week left - see what you can do positively. Ken's idea about plywood and kit parts is a good start - get something driving so you can get some practice. A moving robot is an asset in any match - you can certainly block your opponent's corral and you can push balls even if one at a time. Use the default code - go back to square one and take smaller steps.

BTW - when you get to the competition I think you'll be surprised at how supportive other teams are. No-one will look down on you if your robot is dead, in fact they'll pitch in and try to help you get it started. You will enjoy this event regardless of how you robot performs.

Our rookie robot was named "Kenny" because it got killed every match. But we learned alot and moved on.

And don't use plexiglass/acrylic. Use Lexan/polycarbonate.

Re: Will plexi-glass work?
 

if you go with lexan instead of plexiglass ask for polycarbonate - same stuff much cheaper.....gl

Re: Will plexi-glass work?
 

There is only one plastic strong and tough enough. LEXAN.
All, that is All of the other and cheaper choi :) ces will crack and let you down. I can tell you this after 4 years of experience.

Re: Will plexi-glass work?
 

any chance of using lexa or plexiglass for a base is nto good. I am guess you are a rookie team. We use lexan to protect the compenents of our robot and for skins. Lexan is strong but not made to be a base. I would not quit yet but i would suggest go get some wood like mentioned about and just build it out of wood. Especially with a game that i think is gonna involve alot of contact between robots like last year youa re gonna need somethign that holds up

Re: Will plexi-glass work?
 

Didn't plexiglass(acrylic) used to be illegal on FIRST robots since it is so brittle? I know some acrylic got mixed in with our excess stock of polycarbonate, found out the hard way when it shattered while trying to be bent. Eitherway, polycarbonate frames have been done before. In 2001 we had a robot with no structural metal
Browsing the gallery, it looks like team 49 also did a robot made primarily out of lexan

So yes its possible, given your time crunch though, wood might be easier to get and to work with. Just get a drive train that runs first and go from there, there's still plenty of time left. Good luck,
~Scott

Re: Will plexi-glass work?
 

I agree, if you absolutely must use a plastic, use lexan. It is more durable, and while it does splinter and shatter, it is less likely to do besides plexiglass. If you use this, you have to support it, using plexiglass or lexan will no support is a sure way to have a base be totally demolished. Supporting the base with aluminum extursion at stress points (if you can, ask an engineer to evaluate your design and offer advice on where to support it) is a very good idea.

Now Ken is also right. There is absolutely nothing wrong with using plywood as a base. In fact, one team that comes to mind that uses a wood base every year and is one of the well known teams in FIRST is Team 173 Rage. Every year they use a wood frame (which I'm not mistaken is supported by aluminum brackets). It may splinter, but with the brackets, it's an easy fix. Just put a sheet of aluminum or steel over it, bolt it on, and you're ready to go. I bring up Rage, because they are one of the well known teams that uses a wood base, and have so for years.

And yes, if you turn up at your regional with your robot unfinished, it's guarenteed other teams will come over to help you. No team is going to look down upon you, in fact most teams will do everything in their power to make sure your robot works and is able to compete. That's the great thing about FIRST, everyone is willing to help each other to make sure the competition is as good as it can be and everyone has a fighting chance.

Re: Will plexi-glass work?
 

I don't know how physical this years matches will be but last year we shattered the side of a lexan robot in our first practice match (they ran into us). I still have a piece of it.

I would use wood and the aluminum for the kit. You can definitely get something driving and it will cut down on the repairs you will have to do at competition. You can compete if you can make something that can drive every match.

Re: Will plexi-glass work?
 

I disagree there are few other plastics that are better suited for a frame than lexan. Polyethylene is probably one of the better plastics to use for frame materials. It is easy to machine and very durable. The names to look for are HDPE (same stuff used in the fields) and UHMW. My best guess is that the gearbox and mounts are some form of polyethylene.

Re: Will plexi-glass work?
 

I'm sure that if you've gotten this far in this thread, you know that plexiglas (acrylic plastic) is not a good structural material. What might be missed is why you would use one material over another, and how you'd choose the "best" one for your application.

[A little disclaimer here: I am not a mechanical engineer or materials expert - but I do have a tattered degree from the school of hard knocks.]

First - the term "plastic" tells you something right off about these materials: they can deform, move, flow and/or creep by nature. This may be a good thing if you want low friction, impact resistance or high toughness. It also means that in general, their strength may not be the greatest. (There are exceptions to every rule, but we're talking generalities here.)

So, going back to a couple of plastic materials mentioned in this thread, what's so good or bad about acrylic and polycarbonate? Acrylic is great for clarity - you can polish it so it looks like crystal glass. It has pretty good machineability with the right tooling, too, but those tools require a different profile than what you use for metal or wood. It is pretty hard and stiff, but does break easily (notice I compared it with glass earlier). Personally, I really like working with the stuff, but I can't think of anywhere I'd use it on a robot!

Polycarbonate is what they make bullet-proof windows and jet canopies out of. You can bounce a chicken off it at very high speeds. Or another robot at somewhat lower speed. Great flexibility, too, in thin sections. Not so nice to machine, as it tends to grab the cutter and needs coolant to keep from melting, but sheets can be sheared and bent just like sheetmetal. You shouldn't expect holes tapped in it to hold a lot of force, either in tension or shear - use through bolts, nuts and washers. So this is good stuff for the bumpers, feelers, side covers and things that go bump on a robot.

Polyethylene (HDPE, UHMW, LDPE) is great as a sacrificial wearing surface, chain guides for example, and for chemical resistance. It's okay for lightly loaded bearings, but it's a pretty lousy structural material.

One way to look at materials for structures (like robot frames) is their strength to weight ratio. If we compare the ultimate tensile strenght divided by the density we get a picture of why people use steel for fasteners and really strong structures, aluminum for weight-sensitive structures, and plastics for the rest. (The numbers are the ratio of the UTS, in MPa, to Density, in g/cm3)

ASTM A574 Steel: 160
6061 Aluminum: 122
Polycarbonate: 58
Acrylic: 51
Delrin: 48
HDPE: 29
Teflon: 14

[End of lecture]

Re: Will plexi-glass work?
 

well thanks for all your suggestions! i beat it into my team that we needed some kind of metal. we used alumminum and we are still using the plexi glass for walls and the base and the top. I suggested using the stuff that you guys told us to use...but we diddn't. and we are getting our electrical stuff mounted and all that. so i think we can have this done by thursday! i hope we can get it done! Thanks for your help!

Mathew Smith
Team 1352

Re: Will plexi-glass work?
 

Plexi-glass I.E. Acrylic is EVIL it shatters even before you are finished machining it. Therefore it should be avoided like the plague. If you are put into the circustance when someone has a knife to your throat threatening to kill you if you don't use acrylic then the only answer is to use brad point drill bits. But that's about all you can do; Don't mill it, turn it, cut it with a saw, or do anything else because it will break.

However do not dispare there is an answer.

LEXAN, POLYCARBONATE is the answer!!

Tough, Strong, Clear, some varieties are bullet proof. But all varieties of lexan are better than plexi-glass.

Re: Will plexi-glass work?
 

This is slightly tangential, but....
I heard a story that one team used lexan on their robot, and spray-painted it. And the paint and varieties of temperatures caused it to become very brittle and it cracked during their first match. Is there any truth in this at all?

Re: Will plexi-glass work?
 

I'm not sure about "more brittle", but I'm pretty sure spray paint contains a solvent that will damage polycarbonates. I believe ketones (acetone) are the main problem (I know these are damaging to acrylics like Plexiglass). In general, polycarbonates are much more resistent to solvents then acrylics.

In general, keep organic solvents away from polymers :) (I believe there is a thread about this in the Control System forum).

There are spray paints specifically made for polycarbonates. Latex based paints would work (if they stick, I'm not sure).

Greg

Re: Will plexi-glass work?
 

You all are crazy. Lexan can't be shattered, or damaged. Maybe if you buy it down at the local rip off house home imporvement store, it will.

Horray for Lexan!?!?!?!

Re: Will plexi-glass work?
 

Don't forget that wood is a very good option. Over the past 4 years, my team has made 2 robots with aluminum frames and 2 robots with wooden frames. The 2 with aluminum frames lost miserably. The 2 with wooden frames were our pride and joy, and played very well. The success level may just be coincidence, but we definitely did well with wood. Our team found some 9-layer plywood that works real well.

Re: Will plexi-glass work?
 

190's 2k3 robot was almost entirely lexan, and it held up pretty well. The only structural metal we had in the chassis was the two pieces of channel that held our crab drive. If you use a combination of Lexan Glue (which chemically welds pieces together), bolts, and some aluminum angle on the outside corners, you can end up with a pretty strong frame.

Re: Will plexi-glass work?
 

I have heard the same thing. But as for the specific case I don't know of one. It would make since to me since spray paint is very caustic. A good acrylic paint or latex paint should have the same proplem. The best guarentee would be to print of over head projection pages and adhere them to the inside of the lexan.

So be warned of compromising materials with chemicals.

Re: Will plexi-glass work?
 

I have seen lexan shatter but it takes quite a bit to shatter it. The circumstance was in battle bots. A spinning bot got slammed in to the 1/2" thick bullet proof lexan wall and took a chunck out of it the size of a human head. It was pretty spectacular.

But that is way out of the FIRST robotics league.

Re: Will plexi-glass work?
 

This is team 1038 from 2003.

http://www.chiefdelphi.com/forums/pi...gle&picid=3592

Re: Will plexi-glass work?
 

Lexan can easily be damaged. The sun is just one of the many things that can and will weaken it. Loctite is another.

Re: Will plexi-glass work?
 

Polycarb + Heat gun = Messy death. We tried to bend it like that for our control box last year. Oooops.

Other than that, it is a great material to use...however, I don't see why there is so much worry about break-age. The competition this year really isn't as violent as last year's, and I personally think you'll be just fine with Plexi unless you're planning on playing bumper cars with the other bots...

Re: Will plexi-glass work?
 

PLEASE DO NOT USE PLEXIGLASS/ACRILYC (sp??). The volunteers and field crew will thank you if you dont use plexi, i personally spent a good 10 mins with another staff member at the NJ Regional this past weekend cleaning up 1/2 a bot's plexi frame that exploded on contact with another bot while in auton mode. It shatters into small shards like glass will and needs to be all completly removed due to the hazard to the game balls...

Re: Will plexi-glass work?
 

as everyone else has mentioned, plexi has a tendency to break..well, more like shatter. If someone so much as touches the stuff...Id' hate to be you guys if you had a match in less than a few hours

Re: Will plexi-glass work?
 

Our entire base was constructed of lexan. With this we managed to hold up against anyone who tried to push us off the ramp.

This year our robot used lexan plating on an aluminum frame. We decided to play king of the hill on the chin-up platform. The lexan on our robot is merely scratched. You dont have to worry about it breaking in this competition.

Re: Will plexi-glass work?
 

I don't want to repeat anything that's already been said... so I won't mention plexi-glass and the fact that it is completely horrible for use as a structural component on a robot.

But I will say something interesting: We have a cart we've been working on, which is motorized, to carry the robot around on. We gave our 12" wheels to team #1043 before we realized that we might have wanted them for the cart. (A good move, they made very good use of those wheels). However, to get to the point, we actually tried replacing those wheels with 12" roughly cut wheels of lexan instead. Ugly, but they could withstand the pressure, and weight isn't an issue for a cart. We will end up putting the pneumatic tires on, but the cart would have functioned, we expect, with the lexan.

Re: Will plexi-glass work?
 

For many years, we used laser cut lexan wheels on the robot. They gave us limited slip on the carpet and allowed some side turning for tank drive. We never had one break but they did wear down.