Robot is not subjected to gravity and friction

[aleada23]

Good morning,
I'm a student and I'm using Robosuite for a project. I'm trying to move the Baxter robot with his base into the space. In order to do this I introduced 3 more joints at the base (2 prismatic and 1 revolute) into the xml file of the robot to provide mobility.
I substituted the mount with a geom with the same mesh and then the robot moves with it's base. However it slides on the floor without being subjected to friction, also if i put all the coefficients at the maximum values. Then I noticed also that the robot is floating on air and it's not subjected to gravity, so if I introduce a downhill into the floor the robot is not able to follow the shape of the ground.
Can some one help me with the resolution of this two problems?

Thank you for your time,
Alessandro