Polycarbonate/Plexiglass Ruling

[SnowCats]

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]

Originally Posted by SnowCats

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]

Originally Posted by SnowCats

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]

Originally Posted by Ginger Power

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]

A solid block of polycarbonate would cost less than an equivalent block of 7075 aluminum, I think. We can ask Poohbear.

[Ginger Power]

Originally Posted by Ari423

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]

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]

Originally Posted by messer5740

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]

Originally Posted by Ari423

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]

Originally Posted by mrnoble

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]

Originally Posted by cadandcookies

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]

Originally Posted by messer5740

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]

Originally Posted by frcguy

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

Haha yes, I loved that thread!

[Ekcrbe]

Originally Posted by frcguy

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

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

[FrankJ]

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.