Mobile robot gravity issue on gazebo7

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Hello,

I am working with a mobile robot controlling it with ROS controllers.

Lately i decide to upgrade the version to gazebo7.11 but I noticed that robot seems like has no gravity.

Notes:

1. I spawn the robot from urdf.xacro file
2. The same urdf.xacro of the robot and .world file on gazebo2 works correctly
3. The only change that i did, was at the controller of the base which I changed the functionjoints[]->SetMaxForce() to joints_[]->SetEffortLimit() , following this answer.

See what happens when trying to move the robot:

Any ideas on what could go wrong?