Real time tracking control

[nataliya-dev]

Hello!
I would like to implement a loop in which the arm receives a command in real-time and updates its position. The loop can run ~30Hz because there is some computation in between receiving data and sending the command to a robot. However, if I use set_joint_positions() or robot_write_commands() in position mode then I have to wait an arbitrary amount of time before sending another command. This means the robot starts and stops and the motions become slow and out of sync with real-time commands.
I would like to use velocity control, such as robot_write_commands() in velocity mode, but in that case I am cautious about how the robot will behave. For example, sending all zero velocities means the robot joints drop down. To pause robot motion, would I need to set the robot to position mode? Will there be any issues at low velocities? Please let me know if there a better way to implement this real-time tracking loop.