Internal State of Stretch
Getting the State of the Robot
Begin by starting up the stretch driver launch file.
roslaunch stretch_core stretch_driver.launch
Then utilize the ROS command-line tool rostopic to display Stretch's internal state information. For instance, to view the current state of the robot's joints, simply type the following in a new terminal.
rostopic echo /joint_states -n1
Note that the flag,
-n1, at the end of the command defines the count of how many times you wish to publish the current topic information. Remove the flag if you prefer to continuously print the topic for debugging purposes.
Your terminal will output the information associated with the
/joint_states topic. Your
effort information may vary from what is printed below.
header: seq: 70999 stamp: secs: 1420 nsecs: 2000000 frame_id: '' name: [joint_arm_l0, joint_arm_l1, joint_arm_l2, joint_arm_l3, joint_gripper_finger_left, joint_gripper_finger_right, joint_head_pan, joint_head_tilt, joint_left_wheel, joint_lift, joint_right_wheel, joint_wrist_yaw] position: [-1.6137320244357253e-08, -2.9392484829061376e-07, -2.8036125938539207e-07, -2.056847528567165e-07, -2.0518734302754638e-06, -5.98271107676851e-06, 2.9291786329821434e-07, 1.3802900147297237e-06, 0.08154086954434359, 1.4361499260374905e-07, 0.4139061738340768, 9.32603306580404e-07] velocity: [0.00015598730463972836, -0.00029395074514369584, -0.0002803845454217379, 1.322424459109634e-05, -0.00035084643762840415, 0.0012164337445918797, 0.0002138814988808099, 0.00010419792027496809, 4.0575263146426684e-05, 0.00022487596895736357, -0.0007751929074042957, 0.0002451588607332439] effort: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0] ---
Let's say you are interested in only seeing the
header component of the
/joint_states topic, you can output this within the rostopic command-line tool by typing the following command.
rostopic echo /joint_states/header -n1
Your terminal will then output something similar to this:
seq: 97277 stamp: secs: 1945 nsecs: 562000000 frame_id: '' ---
Additionally, if you were to type
rostopic echo / in the terminal, then press the
Tab key on your keyboard, you will see the list of published active topics.
A powerful tool to visualize ROS communication is the ROS rqt_graph package. By typing the following in a new terminal, you can see a graph of topics being communicated between nodes.
The graph allows a user to observe and affirm if topics are broadcasted to the correct nodes. This method can also be utilized to debug communication issues.