Delay in execution about universal_robots_ros2_driver

[fmauch]

Thanks for sharing your thought with us.

I have a couple of remarks:

• You seem to be using a rather old version on an end-of-life ROS version.
• There's definitively a small delay in execution, since the underlying command on the robot controller (servoj) needs some cycles to correctly compute motion commands to get to a target position. It basically needs to look ahead of the next setpoint.
• If you need synchronous motions you should definitively combine both drivers into one controller_manager. I assume, you are already doing that, you just simplified things to demonstrate the problem here.
• I'm not sure about MoveIt!'s role here. You are measuring trajectory execution plus the overhead of the action call. As the latter is not real-time critical this is not deterministic.
• You might be better off using a velocity-based controller, since the expected delay is lower there. However, this currently seems not to be working correctly (see #905)

[kokkalisko]

Just an update:

• I have tried to move the robot to an end position in URSim by publishing a setpoint to the controller topic, but the delay seems to persist.
• According to my timing tests, the added delay due to the MoveIt action call is negligible.

At this point, I strongly think that this is not related to the UR driver (maybe related to the controllers) and I will close the issue. In case I ever come up with a solution I will update it.