How Slippery is the Bridge

[idahorobot]

I am trying to figure out how slippery is the bridge for the 2012 FRC game. I think the specs are saying that the field bridge material will be HDPE. I found the coefficient for that to be .28. That seems quite slick.

The YouTube video show a battery not sliding?

Am I on the right track?

Anyone know for sure?

Thanks ahead!

[Elgin Clock]

HDPE is a slick material. You are correct. You have the COF number, now compare that number with some other material you are familiar with if you don't have access to a piece of HDPE & you'll get an idea of just how slick.

[RufflesRidge]

The bridge surface is polycarbonate. HDPE is the material for the bridge "deck" which is below the polycarb surface.

[DonRotolo]

That is correct. The surface is polycarbonate.

[Mongai]

Originally Posted by Elgin Clock

HDPE is a slick material. You are correct. You have the COF number, now compare that number with some other material you are familiar with if you don't have access to a piece of HDPE & you'll get an idea of just how slick.

Would that be comparable to the Lunacy surface?

[the man]

Sooooo, how slick is polycarbonate?

[Grim Tuesday]

According to Wikipedia, the CoF of polycarb is 0.31

To compare with wood, according to this,

Coefficients of sliding friction for smooth, dry wood against
hard, smooth surfaces commonly range from 0.3 to 0.5; at
intermediate moisture content, 0.5 to 0.7; and near fiber
saturation, 0.7 to 0.9.

[the man]

How much does the coefficient of friction change with wheel composition?

[djdaugherty]

There is no such thing as a coefficient of friction for one material (e.g. polycarbonate). A coefficient of friction is always between two materials (e.g. polycarbonate and rubber or polycarbonate and wood). You will find many examples of CoF between materials because they vary greatly depending upon the composition of the two materials. The CoF values are determined emperically. Your best bet is to purchase a sheet of polycarbonate and play with it.

[the man]

So in other words, Posting the coefficient of friction gives no help at all because it various between materials. We need to experiment. Good thing our mentor has about 20 sheets of 1/8 in polycarbonate lying around. mwahahah.

[PAR_WIG1350]

Originally Posted by the man

So in other words, Posting the coefficient of friction gives no help at all because it various between materials. We need to experiment. Good thing our mentor has about 20 sheets of 1/8 in polycarbonate lying around. mwahahah.

Make sure you remove the masking material, if there is any. If you leave that on, your results will be inaccurate.

[Bill_B]

Originally Posted by PAR_WIG1350

Make sure you remove the masking material, if there is any. If you leave that on, your results will be inaccurate.

What? And get scratches on it? Won't that change the CoF too? You mean Cof will be different in Elims than it was in Quals? week2 differs from week1? Week 6 balancers will have a cake walk on the scratch-covered bridges. Or do you think we'll get fresh polycarb each tournament?

All hail the goddess of uncertainty! I mean, I would if I knew in which direction to genuflect.

[maxwellt]

if your wondering you are pretty much driving on a white board for the ramps which is really slick depending on the wheels you are using for this year, if you use the wheels from the KOP you have no problem on the bridge but if you use mechanum wheels you will be sliding all over the place on the ramp during the game

[the man]

Originally Posted by maxwellt

if your wondering you are pretty much driving on a white board for the ramps which is really slick depending on the wheels you are using for this year, if you use the wheels from the KOP you have no problem on the bridge but if you use mechanum wheels you will be sliding all over the place on the ramp during the game

I dont think so. The mechanum wheels are a soft-ish rubber I think they will grip quite well, I also saw a youtube video of some one going up a bridge with mechanums.

[Samk]

We had some hdpe laying around the shop, took one of the wheelchair wheels to it, the wheel stuck surprisingly well.