I am facing this issue again and again. Before i solved by modefing the inetia values, now i'm again getting the same problem. Whenever i start gazebo with the model, all the links position comes to zero. and i just found out that if i put the pid value as 000, it don't hapens, in this case what p i d values should i use. current controller configuration values are:

rrbot:
  # Publish all joint states -----------------------------------
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50  

  # Position Controllers ---------------------------------------
  joint1_effort_controller:
    type: effort_controllers/JointEffortController
    joint: joint1
    pid: {p: 0.0, i: 0.0, d: 0.0}
  joint2_position_controller:
    type: effort_controllers/JointPositionController
    joint: joint2
    pid: {p: 100.0, i: 0.01, d: 10.0}
  joint3_position_controller:
    type: effort_controllers/JointPositionController
    joint: station_joint
    pid: {p: 100.0, i: 0.01, d: 10.0}

this also happens after few seconds the model has loaded properly in gazebo. the model starts to shake after 10-15 seconds and than everything goes to origin.