Why does gravity not simulate?

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I am trying to make a quadruped robot. I have attached the files of the robot below. It says that gravity cannot be simulated correctly. What should I do to correct it. Also, it says

[ INFO] [1592469924.035582306, 0.001000000]: Starting gazebo_ros_control plugin in namespace: /urdfgenesyssw
[ INFO] [1592469924.037038323, 0.001000000]: gazebo_ros_control plugin is waiting for model URDF in parameter [/robot_description] on the ROS param server.
[ERROR] [1592469924.154172441, 0.001000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/BLLFT

The error occurs even when I have included a yaml file with joint config details with PID parameters, Ill attach a sample below.C:\fakepath\gazebo.launch

The below warning occurs but I have no idea why.

   [ INFO] [1592469924.177225326, 0.001000000]: Loaded gazebo_ros_control.
    [ WARN] [1592469924.177853816, 0.002000000]: The default_robot_hw_sim plugin is using the Joint::SetPosition method without preserving the link velocity.
    [ WARN] [1592469924.177892672, 0.002000000]: As a result, gravity will not be simulated correctly for your model.
    [ WARN] [1592469924.177916895, 0.002000000]: Please set gazebo_pid parameters, switch to the VelocityJointInterface or EffortJointInterface, or upgrade to Gazebo 9.
    [ WARN] [1592469924.177943573, 0.002000000]: For details, see https://github.com/ros-simulation/gazebo_ros_pkgs/issues/612

I am also attaching the YAML FILE CODE.

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

# Position Controllers
joint11_position_controller:
  type: effort_controllers/JointPositionController
  joint: base_link_to_LF_thigh_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint12_position_controller:
  type: effort_controllers/JointPositionController
  joint: LF_thigh_link_to_LF_calf_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint21_position_controller:
  type: effort_controllers/JointPositionController
  joint: base_link_to_RF_thigh_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint22_position_controller:
  type: effort_controllers/JointPositionController
  joint: RF_thigh_link_to_RF_calf_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint31_position_controller:
  type: effort_controllers/JointPositionController
  joint: base_link_to_LH_thigh_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint32_position_controller:
  type: effort_controllers/JointPositionController
  joint: LH_thigh_link_to_LH_calf_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint41_position_controller:
  type: effort_controllers/JointPositionController
  joint: base_link_to_RH_thigh_link
  pid: {p: 200.0, i: 10, d: 10.0}
joint42_position_controller:
  type: effort_controllers/JointPositionController
  joint: RH_thigh_link_to_RH_calf_link
  pid: {p: 200.0, i: 10, d: 10.0}