Checking out friction parameters trying to solve situations involving grasping and a humanoid walking I ended up with a doubt:
If I check mu and mu2 parameters from ground_plane in the different sdf versions they have values like 100 and 50 or 1000 and 500.
Meanwhile sdf documentation (http://sdformat.org/spec?elem=collision&ver=1.4) says it's in range [0..1].
I've tried spawning an inclined box as a ramp and spawning a cube over it and play with it's mu and mu2 values. I found out that anything over 1.0 seems to be treated as just 1.0.
I've tested this on Gazebo 2.2 and Gazebo 4.0.
Here you can see a video of the friction acting like that with a tool I made to spawn a inclined ramp and a cube over it with the parameters I tell it on the fly: https://youtu.be/I_QM5v0xT14
