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Creating a full robot in NXT-ROS

Connect Sensors

For this tutorial, let's add some more sensors and motors: plug in a touch sensor, a color sensor, an ultrasonic sensor, and a servo motor.

• PORT1: intensity sensor
• PORT2: ultrasonic sensor
• PORT3: touch sensor
• PORTA: servo

Create robot.yaml

The yaml file

First, create learning_nxt/robot.yaml in your favorite editor, and place the following inside it:

   1 nxt_robot:
   2   - type: motor
   3     name: l_motor_joint
   4     port: PORT_A
   5     desired_frequency: 10.0
   6   - type: touch
   7     frame_id: r_touch_link
   8     name: touch_sensor
   9     port: PORT_3
  10     desired_frequency: 10.0
  11   - type: ultrasonic
  12     frame_id: r_ultrasonic_link
  13     name: ultrasonic_sensor
  14     port: PORT_2
  15     spread_angle: 0.2
  16     min_range: 0.01
  17     max_range: 2.5
  18     desired_frequency: 10.0
  19   - type: intensity
  20     frame_id: l_intensity_link
  21     name: intensity_sensor
  22     port: PORT_1
  23     color_r: 1.0
  24     color_g: 0.0
  25     color_b: 0.0
  26     desired_frequency: 10.0

The yaml explained

Now, let's break down the ymal piece by piece.

   1 nxt_robot:

Here we are putting everything in the nxt_robot namespace.

   2   - type: motor
   3     name: l_motor_joint
   4     port: PORT_A
   5     desired_frequency: 10.0

These lines creates a motor object with name L_motor_joint that are connected to PORT_A with a pulling frequency of 10Hz.

   6   - type: touch
   7     frame_id: r_touch_link
   8     name: touch_sensor
   9     port: PORT_3
  10     desired_frequency: 10.0

These lines creates a touch object with name touch_sensor and a frame_id r_touch_link of that is connected to PORT_3. The pulling frequency in this case is 10Hz.

  11   - type: ultrasonic
  12     frame_id: r_ultrasonic_link
  13     name: ultrasonic_sensor
  14     port: PORT_2
  15     spread_angle: 0.2
  16     min_range: 0.01
  17     max_range: 2.5
  18     desired_frequency: 10.0

These lines creates an ultrasonic sensor with a spread angle of 0.2m, a min range of 0.01m, and a max range of 2.5m that is connected to PORT_2.

  19   - type: intensity
  20     frame_id: l_intensity_link
  21     name: intensity_sensor
  22     port: PORT_1
  23     color_r: 1.0
  24     color_g: 0.0
  25     color_b: 0.0
  26     desired_frequency: 10.0

These lines creates a intensity object with name intensity_sensor and a frame_id l_intensity_link of that is connected to PORT_1 with the red LED on.

Launch the yaml File

Now we need to create a launch file to launch the robot.yaml file. Create learning_nxt/robot.launch in your favorite editor, and place the following inside it:

<launch>

  <node pkg="nxt_ros" type="nxt_ros.py" name="nxt_ros" output="screen" respawn="true">
    <rosparam command="load" file="$(find learning_nxt)/robot.yaml" />
  </node>

  <node pkg="nxt_ros" type="joint_states_aggregator.py" name="joint_state_publisher" output="screen" />

</launch>

Turn on your nxt brick and connect it to the computer via USB. Now roslaunch:

$ roslaunch robot.launch

You should see something similar to:

• SUMMARY
  ========
  
  PARAMETERS
   * /nxt_ros/nxt_robot
  
  NODES
    /
      nxt_ros (nxt_ros/nxt_ros.py)
      joint_state_publisher (nxt_ros/joint_states_aggregator.py)
  
  starting new master (master configured for auto start)
  process[master]: started with pid [32451]
  ROS_MASTER_URI=http://bvo:11311/
  
  setting /run_id to 281dd58e-afb1-11df-98e9-00251148e8cf
  process[rosout-1]: started with pid [32464]
  started core service [/rosout]
  process[nxt_ros-3]: started with pid [32493]
  process[joint_state_publisher-4]: started with pid [32494]
  [INFO] 1282676127.009863: Creating motor with name l_motor_joint on PORT_A
  [INFO] 1282676127.016516: Creating touch with name touch_sensor on PORT_3
  [INFO] 1282676127.022412: Creating ultrasonic with name ultrasonic_sensor on PORT_2
  [INFO] 1282676127.127735: Creating intensity with name intensity_sensor on PORT_1

Viewing Data

Now you can list all the topics:

$ rostopic list 

Now you can see all the sensor and joint data:

• /intensity_sensor
  /joint_command
  /joint_state
  /joint_states
  /rosout
  /touch_sensor
  /ultrasonic_sensor

You will see topics for each sensor and state/command topics for the joints in this case (motor1 and motor2).

Run:

$ rostopic echo joint_states