Follower

This package contains ROS2 nodes that allow a target robot to follow joint positions published by a teachbot device.

Overview

The teachbot device publishes joint states on /teachbot/<target_robot>/joint_states, and these nodes command the UR robot to move to match those positions.

Quick Start

Launch Control (Recommended)

ros2 launch teachbot_follower follower_action.launch.py

This starts:

• TeachBot follower action client

Available Nodes

1. follower_action ✅ RECOMMENDED - Action Client

This node uses action client to send trajectory goals. Robust with feedback and result handling.

Usage:

ros2 launch teachbot_follower follower_action.launch.py

Parameters:

• teachbot_topic (default: /teachbot/joint_states) - Topic to subscribe to for teachbot commands

• enable_topic (default: /teachbot/enable) - Topic for enable/disable control

• controller_name (default: scaled_joint_trajectory_controller) - Name of the joint trajectory controller

• update_rate (default: 0.5) - Seconds between updates

• position_tolerance (default: 0.01) - Minimum position change (radians) to trigger movement

• trajectory_duration (default: 2.0) - Duration for each trajectory segment

2. teachbot_follower_moveit_commander 📝 Alternative - Direct Commands - Experimental

This node directly publishes trajectory commands to the robot controller.

Usage:

ros2 run teachbot_follower follower_moveit_commander

Parameters:

• teachbot_topic (default: /teachbot/joint_states)

• enable_topic (default: /teachbot/enable)

• controller_name (default: scaled_joint_trajectory_controller)

• update_rate (default: 0.5)

• position_tolerance (default: 0.01)

• trajectory_duration (default: 0.5)

Complete Workflow

1. Build the package:

   cd ~/teachbot_ws
   colcon build --packages-select teachbot_follower --symlink-install
   source install/setup.bash
   

2. Launch your UR robot with MoveIt:

   # For simulation:
   ros2 launch my_ur_bringup simulation.launch.py
   
   # Or for real robot:
   ros2 launch my_ur_bringup real_robot.launch.py robot_ip:=<ROBOT_IP>
   

3. Start your teachbot device (ensure it publishes to /teachbot/joint_states)

4. Run the follower node:

   # For simulation:
   ros2 launch teachbot_follower follower_action.launch.py sim:=true
   
   # Or for real robot:
   ros2 launch teachbot_follower follower_action.launch.py
   

Joint Names

Make sure the joint names in the teachbot message match the UR robot joint names:

• shoulder_pan_joint

• shoulder_lift_joint

• elbow_joint

• wrist_1_joint

• wrist_2_joint

• wrist_3_joint

Troubleshooting

Robot doesn’t move

• Check that /teachbot/joint_states is being published: ros2 topic echo /teachbot/joint_states

• Verify MoveIt is running: ros2 node list | grep move_group

• Check for errors: ros2 topic echo /rosout

Movement is too slow/fast

• Adjust update_rate parameter (lower = faster updates)

• For ur_teachbot_simple, adjust velocity_scaling and acceleration_scaling

• For teachbot_follower_action or teachbot_follower_moveit_commander, adjust trajectory_duration

Joint names don’t match

• Check your teachbot joint names: ros2 topic echo /teachbot/<target_robot>/joint_states --once

• Verify UR joint names: ros2 topic echo /joint_states --once

Safety Notes

⚠️ Warning: This node will command the robot to follow the teachbot positions. Ensure:

• The workspace is clear of obstacles

• Emergency stop is accessible

• The robot is in a safe starting configuration

• You start with slow update rates and small movements to test