How to add controller through calling controller_manager service in C++

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Hi everyone

I meet with a problem with controller_manager. In my project, I need to dynamically delete or spawn a hector_quadrotor. But after spawning a hector_quadrotor in ros-gazebo. It does not have essential topics (cmd/vel and ground_to_truth/pose) for control. I try to call controller_manager/load_controller service to add control/twist controller to it. But it always fails. I did not find much relevant information about how to use service. Does anyone know how to call this service to add controller to the robot in C++

Cheers,

Jason