Bridge material question

I was not sure where to post this exactly, so it can moved by the moderators later.

I would like to know a good place to buy the HDPE. I look places and most are 300+ bucks. I was hoping maybe there is a cheaper place?

FYI
The bridge surface is lexan not HDPE. The key is HDPE.

Also if you don’t know Lexan is a brand name for the material from SABIC. The generic name is polycarbonate which you can get fairly inexpensively for thin sheets.

We bought a sheet from our local plastic supplier for $96.

Another option for teams with a tighter budget, Lexan (or other brand of polycarb) will mimic the behavior of HDPE pretty closely. The question becomes do you need it to be EXACT? or is CLOSE ENOUGH good enough for what you’re doing. I’d say for driver testing, you won’t need anything more accurate than Lexan.

The offical FIRST field drawings say its HDPE. But in the video tour of the bridge they call it polycarbonate.

For what its worth a 48 inch by 48 inch sheet of 1/16th hdpe is about $20 from McMaster + shipping.

The bridge deck is HDPE, that’s the colored part. The bridge surface is a sheet of polycarbonate velcroed on top of the deck.

IMO, the important part to recreate is the surface, which is polycarb. This is what will affect driving characteristics the most.

You are right, I got the bridge deck and surface mixed up.

Would you be able to provide the part number at mcmaster? I haven’t went looking yet but know that there catalog is quite vast in what they carry.

Watch out for shipping on a full 4 x 8" sheet of polycarb.

so im trying to build the seesaw (bridge) and i cant seem to find any plans/blueprints anywhere . can anyone help me out?

8619K427 is the part number for the 48 inch by 48 inch by 1/16 of an inch thick smooth sheet in white.

http://www.usfirst.org/sites/default/files/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2012_Assets/2012TeamDrawings.pdf is the “low cost” (Read: lots of plywood and 2x4’s field elements).

It’s all here:

http://www.usfirst.org/roboticsprograms/frc/2012-Official-FIRST-Field-Drawings

The Competition Manual page on the FIRST web site points to the Field Drawings.

According to FTC Robotics, 2011 -2012 Edition either US Plastics or Mc Master Carr are good sources for this Plastic. We have used TAP Plastic. We have not purchased the plastic for the Bridge yet. We are still building Game pieces. We hope to finish tomorrow. FIRST Team #2643, Mentor

I would also try screen-door and awning installers to find polycarb sheets. they use them instead of glass for their doors.

thank you

hey so i pretty much finished making the bridge and have some concerns.

  1. is it alright to NOT include a pinch guard? whats the worst thatll happen?

  2. the real field will be made out of a kind of plastic which has a different friction than plywood. is the frictional difference that great that lets say if the bot goes fine on the plywood bridge. that it wont go as smoothly on the real field or vice versa?

The competition field does not include the pinch guard, but it is good to have it on your practice bridge to keep people from getting their hands under the bridge. The worse that an happen might include having a finger cut off or some hand bones broken. This won’t happen on the field since there won’t be people getting their hands under the bridge. The most dangerous place is in the hinge assembly. A second danger point is right at the end of the bridge where the bridge meets the floor. If you don’t want to build the entire guard, consider putting a guard over both sides of the hinge.

There is a significant difference between the slickness of a plywood bridge and one with polycarbonate on it. If you can’t afford polycarbonate, consider something e styrene or acrylic which might bee a little less expensive but would be durable enough for practice.

Dr. Bob

Chairman’s Award is not about building the robot. Every team builds a robot.

thank you very much retired starman just one question concerning the bridge. i already finished the plywood version of the bridge and the most i can do is to use a coating to try to mimic the slickness of the actual competition bridge what do u recommend i should get to coat the plywood to accomplish a like slickness to that of the polycarb?