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### URDF coefficients of friction mu1 and mu2 question

Can someone explain what these coefficients of friction mean? From looking at this tutorial it says that "Here mu1 and mu2 are the friction coefficients of the wheels."

http://www.ros.org/wiki/urdf/Tutorials/UnderstandingPR2URDFGazeboExtension

However, when looking at the PR2 urdf for the wheels these coefficients are fairly large (100.0). That seems extremely high for a coefficient of friction.

The coefficient of rubber on dry concrete is 0.6-0.85 for example.

Can someone explain what these coefficients of friction mean? From looking at this tutorial it says that "Here mu1 and mu2 are the friction coefficients of the wheels."
However, when looking at the PR2 urdf for the wheels these coefficients are fairly large (100.0). That seems extremely high for a coefficient of friction.
The coefficient of rubber on dry concrete is 0.6-0.85 for example.