Joint Trajectory Playback Example

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Enable the robot joint trajectory interface, parse a file created using the joint position recorder example, and send a the resulting joint trajectory to the action server.

Code Walkthrough

Joint Position Recorder - Code Walkthrough, Joint Trajectory File Playback - Code Walkthrough


Verify that the robot is enabled from an RSDK terminal session, ex:

$ rosrun baxter_tools -e

Record a joint position file using the example, ex:

$ rosrun baxter_examples -f <example_file>

The recorder is now recording joint positions with corresponding timestamps for both arms. Move the arms while holding the cuffs.

NOTE: You can open and close the grippers while recording by using Baxter's cuff buttons: Oval = Close, Circle = Open

Press any key to exit when done recording.

Start the joint trajectory controller, ex:

$ rosrun baxter_interface --mode velocity

In another RSDK terminal session, Run the joint trajectory playback example program, ex:

$ rosrun baxter_examples -f <example_file>

Both arms will then be commanded to repeat the trajectory recorded during the joint position recording. The difference between this example and the joint_position playback example is that the trajectory controller has the ability to honor the velocities (due to the timestamps) to more accurately repeating the recorded trajectory.


A commonly used ROS method for robot arm motion control is the joint trajectory action interface. The trajectory_controller and it's corresponding joint trajectory action server is the baxter_interface implementation to support this action interface. This example shows usage for launching the joint trajectory action server, and parsing of a text file describing timestamped joint position goals into a joint trajectory action call to be commanded to the joint trajectory action server.

For more information on Baxter's arms, see Using the Arms.


See the trajectory controller's usage on the command line by passing the -h, help argument:

Joint Trajectory Action Server Usage:

$ rosrun baxter_interface -h

usage: [-h] [-l {both,left,right}] [-r RATE]
                                         [-m {position_w_id,position,velocity}]

optional arguments:
  -h, --help            show this help message and exit
  -l {both,left,right}, --limb {both,left,right}
                        joint trajectory action server limb (default: both)
  -r RATE, --rate RATE  trajectory control rate (Hz) (default: 100.0)
  -m {position_w_id,position,velocity}, --mode {position_w_id,position,velocity}
                        control mode for trajectory execution (default:

Joint Trajectory File Playback Usage:

$ rosrun baxter_examples -h

usage: [-h] -f PATH [-l LOOPS]

required arguments:
  -f PATH, --file PATH  path to input file
optional arguments:
  -h, --help            show this help message and exit
  -l LOOPS, --loops LOOPS
                        number of playback loops. 0=infinite.




See the API Reference page for details.

  • Joint Trajectory Action Server - /robot/limb/right/follow_joint_trajectory [control_msgs/FollowJointTrajectoryAction]
  • Joint Trajectory Action Server - /robot/limb/left/follow_joint_trajectory [control_msgs/FollowJointTrajectoryAction]

baxter_interface APIs

  • JointTrajectoryActionServer class:


The arm is not executing the trajectory

Verify that the robot is enabled:

rosrun baxter_tools -e

Verify that the trajectory controller has been started:

rosrun baxter_interface --mode velocity