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Moving the PR2 arm using command line

Description: This tutorial is a brief introduction on how to start up motion planning for the arm.

Tutorial Level: BEGINNER

Setup

To be able to move the arm, three components need to be running:

• perception : this processes the sensor data so it can be used for collision checking. For more details on this, please see collision_map and collision_space

• planning : uses perception information to compute paths for a set of joints. For the purpose of this document we only care about the set joints that make up the right arm. For more details on this, please see planning_environment. The paths consist of a sequence of states (not all planners provide velocity information).

• action interface between planning for the arm and arm controller :

  • listens to requests from the user (for instance, a request to move the arm move_arm),

  • uses the planning component to figure out solution paths,
  • sends the solution paths to the controller so the robot moves,
  • monitors the execution of the path until completion
    • if the path becomes invalid at any point in time, the motion is stopped and a new solution is requested from the planner.

Compiling code

Assuming pr2_alpha (on the robot) or pr2_gazebo (in simulation) are already built, you need to:

   rosmake 3dnav_pr2

Launching things

Assuming the robot is running (or simulation is running):

• Bring up the robot

     roscd pr2_alpha
     roslaunch [pr[e|f|g] | hc[a|b|c]].launch

  • alternatively, if you are running PR2 in simulation, follow the basic simulator tutorials up to this point, and setting

  • export ROBOT=sim

• start perception

     roscd 3dnav_pr2
     roslaunch launch/perception/laser-perception.launch

• Using rviz, check that collision_map_occ topic is being published (you will need the Collision Map panel).On your local machine:

      rosrun rviz rviz

  • Click the "Add" button in the lower left corner of rviz
  • Select "Collision Map" from the pop-up window
  • Click okay, and modify the new "Collision Map" panel to point to the correct topic.
  • Click the "Add" button again
  • Select "Point Cloud" from the pop-up window
    • The point cloud can be used to determine 3D locations of points
      • Select the "View" menu option, and make sure the "Selection" option is enabled
      • Click the "Select" button located near the top left
      • Use the mouse to left-click and drag a box around some points in the point cloud
      • The selected points will appear in a list on the right
• start planning

     roscd 3dnav_pr2
     roslaunch launch/planning/ompl_fake_planning.launch

  • Check the output produced (or the dashboard) and make sure that right_arm appears in the list of known models.

• start action

     roscd 3dnav_pr2
     roslaunch launch/actions/right_arm.launch

  • Make sure the message Starting move_arm for 'right_arm' (IK is enabled) appears and no errors about the action being invalid follow.

Commanding the arm

•    roscd move_arm
     roslaunch launch/arm_cmd_line.launch

  • You should now see a prompt expecting commands for the arm. Type the help command and you should be able to continue from there.

  • The "go" command requires a 3D position. Rviz can be used to select point in a point cloud and print out their positions (see the above section).

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