PlayMotion2

This repository consists of play_motion2, a tool to play and handle pre-recorded motions in ROS2, and its associated messages in play_motion2_msgs. PlayMotion2 allows executing simultaneous trajectories in multiple groups of joints.

Prerequisites

The motions yaml file should follow the following format:

/play_motion2:
  ros__parameters:

    # params for first position approach
    approach_velocity: 0.5        # default 0.5
    approach_min_duration: 0.0    # default 0.0

    motions:
      motion_1:
        joints: [joint1, joint2]
        positions: [0.0, 0.0,
                    0.5, 0.25]
        times_from_start: [0.5, 1.0]
        meta:
          name: Motion_1
          usage: example
          description: 'Example Motion'

      motion_2:
        ...

      motion_3:
        ...

The field positions of the motion_1 there contains two rows and two columns: - Each column corresponds to one joint, so the first column is for joint1 and the second one for joint2 - Each row is one position to reach. Then, motion_1 consists of 2 trajectories for the specified joints: - Trajectory 1: both joint1 and joint2 move from their starting position until reach their respective point 0.0 - Trajectory 2: joint1 goes from 0.0 to 0.5 and joint2 moves from 0.0 to 0.25.

The field times_from_start specifies the time to reach each position from the starting time In case of motion_1 the joints will move to the first position in 0.5s, and to the second position in 0.5s.

However, since the starting position of the joint could be further than expected, an approach time to the first position is calculated for safety reasons. Then, if the approach time for motion_1 is lower than 0.5, the first trajectory will last 0.5s, but if it's higher, it will take the approach time calculated.

The approach velocity and minimum duration can be chosen with their respective parameters.

Usage

In order to use Play Motion 2, it has to be started with the following command

ros2 launch play_motion2 play_motion2.launch.py play_motion2_config:=PATH_TO_MOTIONS_YAML [use_sim_time:=false]

Once started, motion goals can be sent from another terminal:

Disclaimer: In the current version all motions are executed WITHOUT planning.

Planning capability will be available in the future.

ros2 action send_goal /play_motion2 play_motion2_msgs/action/PlayMotion2 "motion_name: motion_1"

PlayMotion2 also includes two services:

• To list the available motions

ros2 service call /play_motion2/list_motions play_motion2_msgs/srv/ListMotions

• To check if a motion is ready to be executed or not

ros2 service call /play_motion2/is_motion_ready play_motion2_msgs/srv/IsMotionReady "motion_key: motion_1"