How to control multiple joint controllers at the same time?

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Assuming you have already set up the controllers through configuration yaml files and modified the urdf to add transmission interfaces then you can use rqt_gui to send commands to each controller.

Once you launch the robot with it's controllers then you can open the rqt gui with a new terminal using

rosrun rqt_gui rqt_gui

From here, there is a drop-down box to select the topic you would like to publish on, it should be something like effort_controllers/JointPositionController/command. Use the plus to add it to the list, modify the rate and expression you would like to publish and repeat for every controller.