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.

[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.

[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.

[Sperkowsky]

Originally Posted by FrankJ

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]

Originally Posted by Sperkowsky

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]

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

[RoboChair]

Originally Posted by Bob Steele

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.

[GreyingJay]

Originally Posted by FrankJ

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]

Originally Posted by GreyingJay

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.