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I am working with Inverted double pendulum in ROS2 Gazebo. I have written a controller which subscribes to /dynamic_joint_states and publishes to /effort_controller/commands of effort controller of ROS2 control to stabilize the links in vertical position.

My controller doesn't seems to be working.

Problem While trying to diagnose the issue, I realize when I echo the effort from /dynamic_joint_states and commanded effort from /effort_controller/commands, I see a lag between the two values.

Example When I command the effort to be 10 for all time, for first 1-2 seconds effort from /dynamic_joint_interface reads 0 then it goes to 10.

I am suspecting this lag to be causing my controller to fail. Even if this is not the issue can someone explain why there's a lag and is there a method to reduce that lag.

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I'm writing here as I couldn't comment yet. Did you write a ROS2 Controller or a ROS2 node?.

If it is a ROS2 node, can you check if the spin is done properly? and also checking the code of the controller (https://github.com/ros-controls/ros2_controllers/blob/bdb7ad5bdcdfec0cd0b17bb05aaf3cac8229e7b5/forward_command_controller/src/forward_controllers_base.cpp#L61C1-L63C84), it writes into the RT Publisher as soon as it gets. You can clone both ros2_controllers and realtime_tools packages and debug it from there

If it is a ROS2 Controller, then you are not supposed to subscribe to the joint states, instead in the state interface ask for ALL (https://github.com/ros-controls/ros2_controllers/blob/bdb7ad5bdcdfec0cd0b17bb05aaf3cac8229e7b5/joint_state_broadcaster/src/joint_state_broadcaster.cpp#L79). Later, use that data to command the interfaces.

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