Frictional Discrepancies

[Tristan Lall]

Originally Posted by AndyMark

Tread Material: White Acetal
...
Coefficient of Friction with plastic surface: 0.5 Static, 0.4 Dynamic

Originally Posted by The Kit of Parts, 10.2.4.1

The wheels supplied in the 2009 KOP are very different from previous years’ kit wheels. The tread material is Celcon M90, and has the following coefficients of friction on white, rippled fiberglass plastic sheet
Inline, static: 0.06
Inline, dynamic: 0.05
Transverse, static: 0.14
Transverse, dynamic: 0.10

There's an order of magnitude between the two sets of published figures (for the inline case, assuming that's how AndyMark tested them). This makes design difficult.

Any guesses as to which is accurate? I'd surmise that AndyMark tested early-production wheels, and that FIRST is quoting from a generic material specification, but that's entirely speculative.

I looked up a Celcon datasheet for bearing design, and (on page 67) they suggest that the dynamic coefficient of friction of Celcon on Nylon 66 is around 0.17, and that for Celcon on steel, it will be between 0.15 and 0.30, depending on speed and pressure. That's a third set of data (albeit only vaguely appropriate to our application), and it falls somewhere in between the other values.

Originally Posted by The Arena, 6.2.1

The REGOLITH is made of “Glasliner FRP^tm” gel-coated, fiberglass-reinforced, polymer material.

Also, note that Section 6 suggests that the floor is the gel-coated Glasliner FRP, while Section 10 (above) states that the sheet is "rippled". According to this and this, the "pebbled" and gel-coat finishes are mutually-exclusive options, so one section must be misleading. Which type of material was used to generate AndyMark's test numbers? Which material will appear at the competitions? (Apparently at the NH kickoff, it was the textured stuff.)