Proposal for low level controller architecture. https://discourse.ros.org/t/is-twist-still-a-good-velocity-command-interface/13218/9

cmd_vel_and_feedback.dot

digraph {

controller [shape=box,label="Controller"];
mixer [shape=box, label="Mixer"];
actuator [shape=box, label="Actuator"];

hardware_interface  [label="Hardware Interface"]
abstract_command [label="Twist"]
constraints [label="Constraints",rank=1]


controller -> abstract_command
abstract_command -> mixer 
mixer -> hardware_interface
hardware_interface -> actuator

constraints -> controller;
mixer -> constraints;

// Force rank for readabilty
{
rank = same
abstract_command -> constraints [style=invis]
rankdir = LR
}

}