ROSCon DE 2023 talk "Learning Robotics Fundamentals with ROS 2 and modern Gazebo"

Slides available here

Setup:

• Follow the official installation instructions at https://docs.ros.org/en/humble/Installation/Ubuntu-Install-Debians.html.
• In the step "Install ROS 2 packages", install the packages ros-humble-desktop and ros-dev-tools.
• In addition, install the following packages

  sudo apt install \
    python3-colcon-common-extensions \
    ros-humble-ign-ros2-control \
    ros-humble-plotjuggler-ros \
    ros-humble-ros2-control \
    ros-humble-ros2-controllers \
    ros-humble-ros-gz-sim-demos \
    ros-humble-ros-ign-gazebo \
    ros-humble-rqt-joint-trajectory-controller \
    ros-humble-rqt-tf-tree
  

M1:

• Start (modern) Gazebo:

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="empty.sdf -r"
  

• Spawn a simple mobile robot in Gazebo:

  ros2 run ros_gz_sim create -file $(pwd)/vehicle_blue.sdf -z 0.325
  

• Create a bridge between ROS and Gazebo:

  ros2 run ros_gz_bridge parameter_bridge \
    '/model/vehicle_blue/cmd_vel@geometry_msgs/msg/Twist]gz.msgs.Twist' \
    '/model/vehicle_blue/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V'
  

• Start PlotJuggler

  ros2 run plotjuggler plotjuggler
  

• Add plots:
  • ROS2 Topic Subscriber -> Select /model/vehicle_blue/pose
  • Drag and drop /model/vehicle_blue/pose/empty/vehicle_blue/translation/x from Timeseries List to the plot area
  • Split the plot vertical twice
  • Add Custom Series -> Input timeseries: Same x as above; Function library: backward_difference_derivative; New name: v; Create New Timeseries
  • Drag and drop v from Custom Series to the middle plot and to the bottom plot
  • Apply filter to data on the bottom plot -> Derivative
  • Now the top plot shows the position x, the middle plot shows the velocity v, and the bottom plot shows the acceleration a.
• Command the mobile robot to move forward:

  ros2 topic pub --once /model/vehicle_blue/cmd_vel geometry_msgs/msg/Twist '
  linear:
    x: 0.1
    y: 0.0
    z: 0.0
  angular:
    x: 0.0
    y: 0.0
    z: 0.0'
  

P1:

• Start Gazebo:

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="$(pwd)/falling_world.sdf"
  

• Create ROS-Gazebo bridge:

  ros2 run ros_gz_bridge parameter_bridge '/model/sphere/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V'
  

• Record pose of falling sphere:

  ros2 bag record /model/sphere/pose
  

• Unpause Gazebo
• Wait for sphere to hit the ground. Stop recording.
• Open bag file in PlotJuggler

P2:

• Start Gazebo:

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="$(pwd)/slippery_slope.sdf"
  

• Create ROS-Gazebo bridge:

  ros2 run ros_gz_bridge parameter_bridge \
    '/model/sphere/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V' \
    '/model/cylinder/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V'
  

• Record pose of falling sphere:

  ros2 bag record /model/sphere/pose /model/cylinder/pose
  

• Unpause Gazebo
• Wait for both objects to have rolled down the inclined plane. Stop recording.
• Open bag file in PlotJuggler

R1:

• Start Gazebo:

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="$(pwd)/stiff_one_armed_bandit.sdf"
  

• Create ROS-Gazebo bridge:

  ros2 run ros_gz_bridge parameter_bridge \
    '/world/stiff_one_armed_bandit/model/double_pendulum_with_base/joint_state@sensor_msgs/msg/JointState[gz.msgs.Model' \
    '/model/double_pendulum_with_base/joint/upper_joint/cmd_force@std_msgs/msg/Float64]gz.msgs.Double' \
    '/model/double_pendulum_with_base/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V'
  

• Unpause Gazebo
• Add /world/stiff_one_armed_bandit/model/double_pendulum_with_base/joint_state/lower_joint/position to PlotJuggler
• Add /model/double_pendulum_with_base/pose/double_pendulum_with_base/double_pendulum_with_base/lower_link/translation/y and z as XY plot to PlotJuggler

R2:

• Start Gazebo:

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="$(pwd)/damped_stiff_one_armed_bandit.sdf -r"
  

• Create ROS-Gazebo bridge:

  ros2 run ros_gz_bridge parameter_bridge \
    '/world/damped_stiff_one_armed_bandit/model/double_pendulum_with_base/joint_state@sensor_msgs/msg/JointState[gz.msgs.Model' \
    '/model/double_pendulum_with_base/joint/upper_joint/cmd_force@std_msgs/msg/Float64]gz.msgs.Double' \
    '/model/double_pendulum_with_base/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V'
  

• Setup plots in PlotJuggler, similar to R1.
• Set torque on upper_joint:

  ros2 topic pub --once /model/double_pendulum_with_base/joint/upper_joint/cmd_force std_msgs/msg/Float64 'data: 3.0'
  sleep 3
  ros2 topic pub --once /model/double_pendulum_with_base/joint/upper_joint/cmd_force std_msgs/msg/Float64 'data: 0.0'
  

• Set friction coefficient of the upper_joint to zero and set the damping coefficient to 0.5:

  <joint name="upper_joint" type="revolute">
    <parent>base</parent>
    <child>upper_link</child>
    <axis>
      <xyz>1.0 0 0</xyz>
      <dynamics>
        <damping>0.5</damping>
        <!-- <friction>1.0</friction> -->
      </dynamics>
    </axis>
  </joint>
  

• Restart Gazebo and repeat the torque command. Observe the difference in the plots.

R3:

• Start Gazebo:

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="$(pwd)/damped_stiff_one_armed_bandit.sdf -r"
  

• Create ROS-Gazebo bridge:

  ros2 run ros_gz_bridge parameter_bridge \
    '/world/one_armed_bandit/model/double_pendulum_with_base/joint_state@sensor_msgs/msg/JointState[gz.msgs.Model' \
    '/model/double_pendulum_with_base/joint/upper_joint/cmd_force@std_msgs/msg/Float64]gz.msgs.Double' \
    '/model/double_pendulum_with_base/pose@tf2_msgs/msg/TFMessage[gz.msgs.Pose_V' \
    '/joint_lower_joint_cmd_pos@std_msgs/msg/Float64]gz.msgs.Double'
  

• Setup plots in PlotJuggler, similar to R1.
• Set torque on upper_joint:

  ros2 topic pub --once /model/double_pendulum_with_base/joint/upper_joint/cmd_force std_msgs/msg/Float64 'data: 50.0'
  

• Set joint position on lower_joint:

  ros2 topic pub --once /joint_lower_joint_cmd_pos std_msgs/msg/Float64 'data: 0.0'
  

• Change the joint position of lower_joint and observe the resulting settling position of the pendulum.
• You can also vary the lower_joint position more continuously:

  for q in $(seq 0 0.1 6.28); do
    ros2 topic pub --once /joint_lower_joint_cmd_pos std_msgs/msg/Float64 "data: ${q}"
  done
  

C1:

• Start Gazebo along with a simulated UR5e robot:

  ros2 launch ur_simulation_ignition ur_sim_control.launch.py
  

• Plot the robot's joint efforts via the /joint_states topic.
• Command trajectories to the simulated robot:

  ros2 launch ur_bringup test_joint_trajectory_controller.launch.py