model set to be immovable still move after collide with other model

**Goal:** I want to set **base_link** of robot arm **fixed to the ground_plane of the world**. When moving robot arm collides with surface of wall, because base_link is fixed to ground, arm has to stop moving(or rather, try to moving to penetrate but doesn't work) instead of the base_link moving away. **Background:** I have learnt how to fix **box model** onto the world from [this question](http://answers.gazebosim.org/question/16419/model-set-to-be-fixed-to-world-keeps-jittering/), by adding static tag of gazebo tag under robot tag in xacro, reference to [using urdf in gazebo](http://gazebosim.org/tutorials?tut=ros_urdf&cat=connect_ros)true However, it doesn't work for the robot arm, though I have done the same trick for robot arm's xacro. Gazebo/Whitetrue Or try this one: true When moving robot arm hits the surface of box, the base_link of robot arm is forced to move away. Original pose of robot arm  Robot arm yields to the inter-force and base_link moves away