ODE Friction Model

[abachoo]

Dear Coppelia

I would like clarification on the friction model used by V-REP for the ODE engine. I refer to an old post (viewtopic.php?f=9&t=5956&p=23946&hilit= ... del#p23946) where this question was raised but not answered.

According to the ODE manual (http://ode.org/wiki/index.php?title=Manual), there are 2 friction approximations to choose from:

• The meaning of μ is changed so that it specifies the maximum friction (tangential) force that can be present at a contact, in either of the tangential friction directions.
• The friction cone is approximated by a friction pyramid aligned with the first and second friction directions. This differs from a true friction pyramid in that the "effective" μ is not quite fixed. This approximation is easier to use as μ is a unit-less ratio the same as the normal Coloumb friction coefficient, and thus can be set to a constant value around 1.0 without regard for the specific simulation.

Which of these 2 options does V-REP use? Based on my experiments, I think option 1 is implemented because the friction values can take on values greater than 1.0. I would also like to know if ODE has a torsional friction model. I came across a Gazebo post saying ODE offers this model but I could not find anything in the ODE manual.

Thank you very much.

[coppelia]

Hello,

the implemented friction model is the second one. The firction coefficient is not limited, and can be specified higher than 1.0, because ODE internall also does not limit that.
Have maybe also a look at the contact callback function, that allows to modify some of the contact parameters on the fly?

Cheers