Joint Trajectory Controller: Joints on incoming trajectory don't match the controller joints

Question

I am trying to create a script to control my robot using an action. The action server was already created by Joint Trajectory Controller and I had to make the action client. The issue I am having is that it continues to give me this error:

Joints on incoming trajectory don't match the controller joints.

I assume the reason I am getting this error though is because my yaml file keeps giving me this message, which isn't given as an error message but a info message:

No specific joint names are used for command interfaces. Using 'joints' parameter.

I do not understand why though because I am using a generic Joint Trajectory Controller yaml setup that is supposedly setup correctly, here it is:

controller_manager:
  ros__parameters:
    update_rate: 100 #Hz

    arm_controller:
      type: joint_trajectory_controller/JointTrajectoryController  

    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster

arm_controller:  
  ros__parameters:
    joints:
      - shoulder_pan_joint
      - shoulder_lift_joint
      - elbow_joint
      - wrist_1_joint
      - wrist_2_joint
      - wrist_3_joint

    command_interfaces:
      - position
    
    state_interfaces:
      - position
      - velocity

As of now I am just trying to control a single joint on the robot, which happens to be the Elbow joint. I am able to control it through rqt but am trying to get actions working. Here is a snippet of my code for the action client that tells it which joint to use:

    def __init__(self):
        super().__init__('move_elbow_actionclient')
        self._action_client = ActionClient(
            self, FollowJointTrajectory, '/arm_controller/follow_joint_trajectory'
        )
#where the goal gets sent
    def send_goal(self, angle):
        goal_msg = FollowJointTrajectory.Goal()

#what joint it controls
        joint_names = ["elbow_joint"]

Thank you for your support and if any more information is needed please let me know!

Answer 1

The Joint_names inside the action client have to entirely match with the joints: parameter in the yaml file, so I put all 6 inside the joint_names and it fixed my problem

Answer 2

Exactly, you have to give all joints in the trajectory message or set allow_partial_joints_goal=true, see the docs.