Interpertation on Bumpers: Do the bumpers need to display the team numbers?

[Mike Betts]

Originally Posted by kws4000

For the past, what, 3 years now, we have used plexi for the electrical box, becouse it doesn't bend under load. Never had a problem. Asides from that, true, lexan is much more resilient under shock.

Back in the 90's, Plexiglass was explicitly forbidden on the robot by rule. When the ban was lifted, I bought a small sheet at the HD for an electrical panel. When it shattered during routine tooling, we went back to polycarb and never looked back.

No team I have ever mentored has ever had Plexiglass on their robot.

To the original poster: If the rules don't persuade you, note this quote from this document:

Team number displayed with 4” tall x ¾” stroke, on the bumpers, 4 locations at approximately 90 deg spacing, in contrasting color or background.<R9>

Without the team number on the bumpers as specified, you will not pass inspection.

Regards,

Mike

[Thermal]

Originally Posted by Al Skierkiewicz

Let this be your guide... I predict 50% of the robots on the field will have an arm for scoring at least the center rows. That means at least one robot on the opposite alliance in every match will have extensions beyond their frame perimeter. Those arms will reach over six feet and can contact your plastic signage.

It's more than just that. Simple vibrations will crack the acrylic where the bolts go through to mount it to your backing. Acrylic is not acceptable for a FIRST robot under any circumstances. If I won't use it in my computer for waterblock tops (where there is negligible vibrations and no movement), you definitely shouldn't ever use it on a FIRST robot.

Theres a few companies (Thermaltake) that used to make waterblocks with acrylic tops and meager 10°C changes to the acrylic along with the pressure the barbs put onto the threadings to maintain a watertight seal caused many of these blocks to crack and leak water over the users video cards and motherboards.

[Matt C]

I find it interesting that this post has turned into a post on acrylic vs polycarbonate.

With students, I normally do the "vise test" . .

Give a student (with safety glasses of course) a small piece of polycarb and tell them to smack it against the vise.

Then give them a piece of acrylic and tell them to do the same thing.

That'll teach em.

(and yes, you need to put your numbers on your bumpers . . silver Sharpie works GREAT!
http://www.amazon.com/Sharpie-MARKER.../dp/B001GXFNYI)

[Grim Tuesday]

We used plexi (acrylic) to make a mounting bracket for our C-Rio, since we have access to a laser cutter, which can't cut polycarb. It allowed us to precisely "drill" the holes for the bottom of the C-Rio, and mount it in a way that it won't crack.

But then we took it off for weight and made a smaller bracket by hand out of polycarb

[Wayne TenBrink]

Is there any difference between "plexiglass" and "acrylic"? I have seen stuff marketed as "plexiglass" that was very brittle and virtually impossible to drill holes in without cracking. We have had decent success with "acrylic" sheet (as marketed by Ace Hardware), for non-structural, flat panels that are well supported along the edges. It drills fairly well, and is quite flexible, but will break before it bends. In 2009 we had 3 large panels (30" x 44") of the stuff and they held up very well despite impacts that bent the supporting structure (yeah, I know - that was Lunacy and there weren't arms and impacts weren't like they are on carpet).

We have three small, non-structural panels of it on the robot this year (because I had a tightwad moment and it was in stock), and we are taking bets about how long it holds up. Will replace any broken sections with Lexan, though.

[Matt C]

Originally Posted by Wayne TenBrink

We have three small, non-structural panels of it on the robot this year (because I had a tightwad moment and it was in stock), and we are taking bets about how long it holds up. Will replace any broken sections with Lexan, though.

I got my money on 2nd practice round.

[Al Skierkiewicz]

Originally Posted by Grim Tuesday

We used plexi (acrylic) to make a mounting bracket for our C-Rio, since we have access to a laser cutter, which can't cut polycarb.

We cut poly on our laser cutter all the time. We have even used it for wheels in the distant past also cut by the laser. It does require some serious deburring operations and the smell takes a while to get used to.

[sanddrag]

I thought I've read polycarb is dangerous to laser cut, due to toxic gasses produced? Can anyone confirm or deny?

[Al Skierkiewicz]

The laser bed we use has fume removal built in.

[Racer26]

1075 used plexiglas on our 2003 electrical board. We had to remake that board several times, and the competition robot had chunks missing from where it had cracked and we couldn't fix it.

Never again have we used it. We switched to some super-thin aluminum sheeting (in the neighborhood of 0.008", IIRC) for our electrical panels since then.

[PAR_WIG1350]

Originally Posted by 1075guy

1075 used plexiglas on our 2003 electrical board. We had to remake that board several times, and the competition robot had chunks missing from where it had cracked and we couldn't fix it.

Never again have we used it. We switched to some super-thin aluminum sheeting (in the neighborhood of 0.008", IIRC) for our electrical panels since then.

??? Aluminum foil???

Also, why not use polycarb? You won't short stuff out by drilling into it, and you can mount your crio directly to the polycarbonate which can then be directly attached to the frame without any additional insulation.

[Matt C]

Originally Posted by PAR_WIG1350

Also, why not use polycarb? You won't short stuff out by drilling into it, and you can mount your crio directly to the polycarbonate which can then be directly attached to the frame without any additional insulation.

Most teams I've worked with use plywood to mount electonics . . .

[Bill_B]

Originally Posted by Wayne TenBrink

Is there any difference between "plexiglass" and "acrylic"? I have seen stuff marketed as "plexiglass" that was very brittle and virtually impossible to drill holes in without cracking.

There is a drill for plastics that has a steeper angle at the tip. I have no recommendation but you could try here for at least the claim of flawless holes in plastics.

[MagiChau]

Originally Posted by Matt C

Most teams I've worked with use plywood to mount electonics . . .

Polycarbonate is what my team uses every year now. It worked fine for us and saves plenty of weight.

[Chris is me]

Originally Posted by Al Skierkiewicz

We cut poly on our laser cutter all the time.

A small, benchtop laser cutter found in many schools would be unable to do this - only huge ones in plastic shops.