DART restitution coefficient not working

[axkoenig]

Hi,

I am using Gazebo 11 and the DART physics engine. I would like to alter the amount of restoring force and damping that is applied when two models in my simulation collide. As I understand this can be altered with the <restitution_coefficient> tag in my SDF. Please correct me if I'm wrong.

I noticed, however, that Gazebo 11 currently ignores the <restitution_coefficient> defined under <bounce> in the SDF. This should be an easy fix. Instead of working with the default DART properties defined here, we could parse at least the <restitution_coefficient> from the SDF and hand it to the constructor.

Note that there is a similar PR open in the IgnitionPhysics repo. Is there an easy way to integrate this change?

[azeey]

It would be nice to add this, but we can't directly take the changes from ign-physics and apply them here. We would need to add a restitution_coefficient variable to DARTSurfaceParamsPrivate.hh and populate it from SDF in DARTSurfaceParams.cc and apply it to the body node in https://github.com/osrf/gazebo/blob/63d11b695134c7075161f1bdc36b91db47f27f92/gazebo/physics/dart/DARTLink.cc#L249

We would definitely welcome a PR ;)