Robot is moving in gazebo even if gravity is turned off [closed]

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Hey,

I am quite new working with ROS and gazebo. I am trying to get the Franka Emika Panda working in gazebo. I am using the offical franka_ros repository: https://github.com/frankaemika/franka.... I modified the urdf files where I got inspired from the repository of erdalpekel: https://github.com/erdalpekel/panda_s....

I am facing the following problem: I start an empty world in gazebo in paused mode and spawn the robot. I don't have any controllers added for this. Now I manually change the gravity value in the gazebo gui to 0.0. Then I start the simulation. What happens is that my robot starts moving around like crazy. I guess it should be completely stable when gravity isn't applied.

I am using revolute and prismatic joints and integrated the gazebo_ros_control plugin. I already made the following investigation:

When the safety_controller-tag is commented out and the values for limit effort and velocity are higher than the orginal (from franka_ros repository), the robot is almost stable. The finger joints are moving and all the other joints are moving a tiny little bit, but it's almost not noticable. I have no idea why these parameters are affecting the movement of the robot when gravity is turned off.

I am battling this issue for quite a while now and don't have any ideas anymore. Maybe I am missing an important detail. So any kind of advice is much appreciated. I also posted this question in gazebo answers.

Thilo

P.S. I am using Ubuntu 18.04 in VirtualBox, Ros Melodic and Gazebo 9.16.0