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SnowCats 19-01-2017 19:12

Polycarbonate/Plexiglass Ruling
 
I was looking through the game manual for this year's competition and I couldn't find anything about the amount of polycarbonate/plexiglass you are allowed to use

Is there a rule on how much you can use?

If so, how much?

pilleya 19-01-2017 19:14

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by SnowCats (Post 1633671)
I was looking through the game manual for this year's competition and I couldn't find anything about the amount of polycarbonate/plexiglass you are allowed to use

Is there a rule on how much you can use?

If so, how much?

You can use as much as you like as long as it is under the allowed total cost of $4000. Probably best to stick to polycarbonate for robot parts to avoid disappointment.

Ginger Power 19-01-2017 19:15

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by SnowCats (Post 1633671)
I was looking through the game manual for this year's competition and I couldn't find anything about the amount of polycarbonate/plexiglass you are allowed to use

Is there a rule on how much you can use?

If so, how much?

There is no limit to how much polycarbonate you can use on your robot. The only rule that applies would be the 120 lb robot weight limit. Be careful how you budget your weight!

edit: ^^^ also the $4000 robot budget limit, and the $400/part limit

Ari423 19-01-2017 19:22

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Ginger Power (Post 1633678)
There is no limit to how much polycarbonate you can use on your robot. The only rule that applies would be the 120 lb robot weight limit. Be careful how you budget your weight!

edit: ^^^ also the $4000 robot budget limit, and the $400/part limit

This raises the question: if you built your entire 120lbs robot out of polycarb, would you exceed the $400 part limit (if it were one solid block) or $4000 total cost limit (if it were laminated sheets)? Someone with too much free time want to do the math?

mrnoble 19-01-2017 19:34

Re: Polycarbonate/Plexiglass Ruling
 
A solid block of polycarbonate would cost less than an equivalent block of 7075 aluminum, I think. We can ask Poohbear.

Ginger Power 19-01-2017 19:37

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Ari423 (Post 1633682)
This raises the question: if you built your entire 120lbs robot out of polycarb, would you exceed the $400 part limit (if it were one solid block) or $4000 total cost limit (if it were laminated sheets)? Someone with too much free time want to do the math?

Or just ask ask a team that basically does build their entire robot out of polycarb.

messer5740 19-01-2017 22:47

Re: Polycarbonate/Plexiglass Ruling
 
Ok learn from our mistakes!! DO NOT use Plexiglass as an electronics board! We had ours made of Plexiglass last year, and by the end of our third time on the field, it was falling apart. By the time eliminations came around, we were on the field with an electronics board held together mostly by duct tape. Poly carbonate is definitely the better choice.

cadandcookies 19-01-2017 22:57

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by messer5740 (Post 1633774)
Ok learn from our mistakes!! DO NOT use Plexiglass as an electronics board! We had ours made of Plexiglass last year, and by the end of our third time on the field, it was falling apart. By the time eliminations came around, we were on the field with an electronics board held together mostly by duct tape. Poly carbonate is definitely the better choice.

This. So many people just call clear plastic "plexi" or "plexiglas"-- whether it's the right thing or not. For competitive robotics, it is just about always the wrong thing.

Also, since nobody explicitly stated what will go wrong:
Lexan basically doesn't shatter. They use specific compositions of it for bulletproof "glass" for this reason. You can even cold-bend the stuff (though I wouldn't generally recommend it) and depending on the use it can be fine. Acrylic on the other hand... well, drop it or hit it with something or try to bend it and see what happens. It shatters. Something into sharp shards. A quite undesirable characteristic for robots. So, polycarbonate, Lexan, or Makrolon are generally good for robot use. Acrylic, Plexiglas, Acrylite, Lucite or Perspex = bad news.

To reiterate everyone else:

Make sure what you are using is polycarbonate and not acrylic or it may very well literally shatter your dreams.

Kevin Sevcik 19-01-2017 23:01

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Ari423 (Post 1633682)
This raises the question: if you built your entire 120lbs robot out of polycarb, would you exceed the $400 part limit (if it were one solid block) or $4000 total cost limit (if it were laminated sheets)? Someone with too much free time want to do the math?

50lbs of PC resin = $175 so $420 for 120 lbs. I'm going to assume we use the bulk price of the resin. Otherwise your robot is free cause each pellet < $5. Actually, I think it's costed at the cost of the smallest amount you can actually buy that covers what you used. So if a carbon fiber resin only comes in $1000 drums, you're out of luck.

According to midwest steel supply, a 24"x24"x2" plate of 7075 regularly costs $440 and weighs in at 116lbs.

frcguy 19-01-2017 23:12

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by mrnoble (Post 1633687)
A solid block of polycarbonate would cost less than an equivalent block of 7075 aluminum, I think. We can ask Poohbear.

You'd need a 5-axis mill and hexagonal wheels too.

engunneer 19-01-2017 23:15

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by cadandcookies (Post 1633780)
This. So many people just call clear plastic "plexi" or "plexiglas"-- whether it's the right thing or not. For competitive robotics, it is just about always the wrong thing.

Also, since nobody explicitly stated what will go wrong:
Lexan basically doesn't shatter. They use specific compositions of it for bulletproof "glass" for this reason. You can even cold-bend the stuff (though I wouldn't generally recommend it) and depending on the use it can be fine. Acrylic on the other hand... well, drop it or hit it with something or try to bend it and see what happens. It shatters. Something into sharp shards. A quite undesirable characteristic for robots. So, polycarbonate, Lexan, or Makrolon are generally good for robot use. Acrylic, Plexiglas, Acrylite, Lucite or Perspex = bad news.

To reiterate everyone else:

Make sure what you are using is polycarbonate and not acrylic or it may very well literally shatter your dreams.

That being said, (and all of it accurate) you can also weaken polycarbonate significantly with some chemicals. Threadlock in particular can make even polycarbonate brittle.

jnicho15 19-01-2017 23:24

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by messer5740 (Post 1633774)
Ok learn from our mistakes!! DO NOT use Plexiglass as an electronics board! We had ours made of Plexiglass last year, and by the end of our third time on the field, it was falling apart. By the time eliminations came around, we were on the field with an electronics board held together mostly by duct tape. Poly carbonate is definitely the better choice.

We made the fan/lid over our electronics last year out of plexiglass. The first defense we crossed, it broke.

Eryl2000 19-01-2017 23:43

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by frcguy (Post 1633786)
You'd need a 5-axis mill and hexagonal wheels too.

Haha yes, I loved that thread! :D

Ekcrbe 20-01-2017 00:37

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by frcguy (Post 1633786)
You'd need a 5-axis mill and hexagonal decagonal wheels too.

Fixed that for you. Also, they need to be arranged holonomically.

FrankJ 20-01-2017 08:50

Re: Polycarbonate/Plexiglass Ruling
 
To restate what others have already said.

Plexiglass is a brand name of acrylic.

Lexan is a brand name of polycarbonate.

They both have their advantages, but acrylic is brittle compared to polycarbonate.. You should avoid using for shields and structural partc. It is nice for fish tanks if we ever have a water game. One easy test to tell acrylic from poly. Hit a piece hard against a table top. If it cracks or shatters it is probably acrylic. Wear your safety glasses. So in the robot world. Lexan=polycarbonate=good. Plexiglass=acrylic=bad.

Sperkowsky 20-01-2017 09:36

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by FrankJ (Post 1633850)
It is nice for fish tanks if we ever have a water game.

Is this a good place for a debate on Glass Vs. Acrylic when building Aquariums?
#teamglass

FrankJ 20-01-2017 10:32

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Sperkowsky (Post 1633862)
Is this a good place for a debate on Glass Vs. Acrylic when building Aquariums?
#teamglass

Only in the context of a water game. :]

Bob Steele 20-01-2017 13:17

Re: Polycarbonate/Plexiglass Ruling
 
Transparent Aluminum?
http://www.ubergizmo.com/2015/11/transparent-aluminum/

although this is really alumina based glass instead of silica based glass
Probably not the same stuff as on Star Trek lol

Oblarg 20-01-2017 13:20

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by cadandcookies (Post 1633780)
This. So many people just call clear plastic "plexi" or "plexiglas"-- whether it's the right thing or not. For competitive robotics, it is just about always the wrong thing.

Also, since nobody explicitly stated what will go wrong:
Lexan basically doesn't shatter. They use specific compositions of it for bulletproof "glass" for this reason. You can even cold-bend the stuff (though I wouldn't generally recommend it) and depending on the use it can be fine. Acrylic on the other hand... well, drop it or hit it with something or try to bend it and see what happens. It shatters. Something into sharp shards. A quite undesirable characteristic for robots. So, polycarbonate, Lexan, or Makrolon are generally good for robot use. Acrylic, Plexiglas, Acrylite, Lucite or Perspex = bad news.

To reiterate everyone else:

Make sure what you are using is polycarbonate and not acrylic or it may very well literally shatter your dreams.

Just about the only nice property of acrylic, in my opinion, is that it lasercuts very, very nicely.

RoboChair 20-01-2017 13:34

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Bob Steele (Post 1633987)
Transparent Aluminum?
http://www.ubergizmo.com/2015/11/transparent-aluminum/

although this is really alumina based glass instead of silica based glass
Probably not the same stuff as on Star Trek lol

Ruby and Sapphire are both transparent aluminum(Al2O3). Sapphire is sometimes used as viewing windows in ultra high pressure and high temperature lab equipment. The color of ruby and sapphire is just based on the impurities in the crystal lattice, no impurities and it's clear like glass.

btw: this means all the aluminum you own is literally covered in sapphire.

Munchskull 20-01-2017 13:40

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Oblarg (Post 1633988)
Just about the only nice property of acrylic, in my opinion, is that it lasercuts very, very nicely.

You laser cut acrylic and you are a hero. You laser cut ABS and you poison the entire shop with cyanide gas. (For real though when lasercuting know the material safety properties.)

RoboChair 20-01-2017 13:49

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Munchskull (Post 1633998)
You laser cut acrylic and you are a hero. You laser cut ABS and you poison the entire shop with cyanide gas. (For real though when lasercuting know the material safety properties.)

And PVC makes chlorine gas

Andrew Schreiber 20-01-2017 13:54

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Munchskull (Post 1633998)
You laser cut acrylic and you are a hero. You laser cut ABS and you poison the entire shop with cyanide gas. (For real though when lasercuting know the material safety properties.)

This is why above our laser cutter we have a list of banned materials. And a fume hood that must be running or the laser won't turn on.

Oblarg 20-01-2017 13:56

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Andrew Schreiber (Post 1634007)
This is why above our laser cutter we have a list of banned materials. And a fume hood that must be running or the laser won't turn on.

Yep, this is the way to go. Back when I was in a lab which laser cut things regularly, we had a big materials chart with safety information and tips about how well the various stuff cut.

Several entries had no text other than "TOXIC FUMES, DO NOT CUT."

Munchskull 20-01-2017 14:00

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Andrew Schreiber (Post 1634007)
This is why above our laser cutter we have a list of banned materials. And a fume hood that must be running or the laser won't turn on.

Correct me if I am wrong but Polycarbonate has dangerous gases too.

RoboChair 20-01-2017 14:03

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Munchskull (Post 1634015)
Correct me if I am wrong but Polycarbonate has dangerous gases too.

I just know it cuts like crap. It puts the carbon back into polycarbonate.

Oblarg 20-01-2017 14:03

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Munchskull (Post 1634015)
Correct me if I am wrong but Polycarbonate has dangerous gases too.

Correct.

It also cuts like crap, though, so it's sort of immaterial.

cadandcookies 20-01-2017 14:04

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Munchskull (Post 1634015)
Correct me if I am wrong but Polycarbonate has dangerous gases too.

It generates benzene if I remember correctly, which is carcinogenic (even in places that aren't California).

Also doesn't cut well.

frcguy 20-01-2017 14:15

Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by RoboChair (Post 1634003)
And PVC makes chlorine gas



Cut Kydex on laser, created chlorine gas. 0/10 would not recommend.

Edit: forgot to add it causes every steel part in your laser to rust. So yeah, don't cut PVC.

Andrew Schreiber 20-01-2017 14:16

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Munchskull (Post 1634015)
Correct me if I am wrong but Polycarbonate has dangerous gases too.

It's on our list - if I recall the training correctly it's partially because it cuts like crap too because it just melts.

We borrowed our list from http://atxhackerspace.org/wiki/Laser...HESE_MATERIALS

Bob Steele 20-01-2017 14:48

Re: Polycarbonate/Plexiglass Ruling
 
Waterjets cut all of these materials pretty well with no fumes.

Oblarg 20-01-2017 14:54

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Bob Steele (Post 1634057)
Waterjets cut all of these materials pretty well with no fumes.

When convenient, affordable desktop waterjets exist, I'll look into them for sure.

engunneer 20-01-2017 16:45

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by Oblarg (Post 1634063)
When convenient, affordable desktop waterjets exist, I'll look into them for sure.

they are now in the $5000 range. https://www.wazer.com/

It was really nice to work for a waterjet maker back when I was on 1318. our 2009 robot was made all of waterjet polycarbonate sheet (which was recylced from a building demolition!)

Our 2008 robot had a waterjet 1/4" titanium sheet as the only frame element. everything just bolted right to it. it also has infinite rotation swerve drives using waterjet copper sheet for custom slop rings.

frcguy 20-01-2017 18:33

Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by engunneer (Post 1634125)
they are now in the $5000 range. https://www.wazer.com/

Quote:

Originally Posted by Cory (Post 1606692)
My opinion is that the Wazer is absolutely useless for FRC purposes (but cool as a technology demonstration).

It cuts REALLY slowly, the cutting area isn't large enough for more than a few small parts, the cost to run it is high, and accuracy will be questionable compared to an industrial water jet. Maintenance will likely add up to more than the cost of the machine within a few years depending on how much its used.

You'd get a lot more mileage out of paying for $5000 (plus cost of consumables) of waterjetting from a legit vendor.

A legitimate water jet cutter is going to be $100-200k depending on how it's optioned out, plus a minimum of $45/hr (up to $60+/hr) to run in power/abrasive/water/amortized maintenance. They are very finnicky and constantly have little problems that pop up that require you to stop and clean things out or perform minor fixes. When the pumps reach their service intervals you're looking at a multi-thousand dollar rebuild. The mixing tubes/orifices are not cheap either and need somewhat frequent replacement. These are also enormously loud and messy machines. Glenn can speak more to his experience with ownership of one, but it would take a unique set of circumstances for a team to have a shop that is suited to owning one.

Legitimate metal cutting lasers for FRC use (1/4" aluminum) are so expensive they're not even worth discussing. $200k-400k. Huge power requirements, though much cheaper to run than water jet due to fewer consumables and lower maintenance costs. These are machines designed to cut 4'x12' sheets all day long as fast as possible and people who own them have to run the machine virtually nonstop, often for multiple shifts a day to make any money off them. Just totally in a whole other world than FRC usage,


Not sure about the Wazer.

JohnFogarty 20-01-2017 18:58

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by frcguy (Post 1634185)
Not sure about the Wazer.

From the short amount of research I did. It takes about $5000 to get 1 ipm of cutting speed for waterjet machines using 1/4" aluminum as a baseline material.

engunneer 21-01-2017 22:54

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by JohnFogarty (Post 1634191)
From the short amount of research I did. It takes about $5000 to get 1 ipm of cutting speed for waterjet machines using 1/4" aluminum as a baseline material.

and to compare to industrial level waterjets, a 60ksi jet can cut 1/4" Aluminum at 22 inches per minute with a nice cut, and ~55 ipm if you tear through it at max speed and don't care about the cut.

dmaggio744 21-01-2017 23:25

Re: Polycarbonate/Plexiglass Ruling
 
As exciting as waterjets are, my team has found huge success with desktop CNC routers. They are relatively cheap, relatively intuitive to use, and cut softer materials like wood and polycarb very easily, and are advertised to cut aluminum if you know what your doing.

We use a Shapeoko 3 XL with DeWalt Router and it's become our new favorite tool. It has a build volume of 33" by 17", and comes with very easy to use software. Our XL version is about $1,600, abut you can scale up(XXL 33" by 33") or down(Standard 16" by 16"). Feel free to pm me if your skeptical, on the fence about buying one, or just want to know more! :D

GreyingJay 24-01-2017 11:27

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by FrankJ (Post 1633850)
One easy test to tell acrylic from poly. Hit a piece hard against a table top. If it cracks or shatters it is probably acrylic. Wear your safety glasses. So in the robot world. Lexan=polycarbonate=good. Plexiglass=acrylic=bad.

The test I was taught (not sure how accurate) is to look into the cross section. If it's clear, it's acrylic. If it's dark, it's polycarbonate.

I have also done an experiment for a non-FRC related group of kids. I took two identically sized pieces of polycarbonate and acrylic plastic (about 2" by 12"). (Fun note: polycarbonate is easy to cut with woodworking power tools like miter saws. Acrylic, I scored with a knife and snapped.)

To the eye, other than the cross section, both pieces look very similar. Then I folded the polycarbonate in half like a sheet of paper. You end up with a nice 90-degree bend. Then I tried the same with the acrylic, and it shatters into pieces (wear gloves). Insert your favourite object lesson here about things looking the same but being very different inside, don't judge inward strength by outward appearances, looking OK on the outside but handling stress and pressure very differently on the inside, etc.

FrankJ 24-01-2017 12:04

Re: Polycarbonate/Plexiglass Ruling
 
Quote:

Originally Posted by GreyingJay (Post 1635570)
The test I was taught (not sure how accurate) is to look into the cross section. If it's clear, it's acrylic. If it's dark, it's polycarbonate.

I have not heard that. It might be possible. They have different optical properties. Acrylic is "brighter". It might be something that a person regularly working with both can judge. I would be hesitant using that criteria as a relatively non expert.


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