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I'm not sure if I understand your question correctly but since you use a joint of type continuous between the links arm1-11 and arm2-11, arm2-11 will rotate around arm1-11.

When no controller is running which is the case when you start up gazebo, no forces are applied to the arm but gravity which might cause the arm link to rotate. You can find some information on how to specify controllers here. To control the arm, you can also use the ros_controller_manager plugin. You can find some information on that here, though I couldn't find a tutorial on that.