how to model motor voltages on the quadrotor

[frewenta]

As I understand it there are Gazebo plugins that calculate propulsion and drag forces acting on the quadrotor but the plugin requires as INPUT the 4 motor voltages (and, perhaps, a wind vector) and then OUTPUTs calculated forces and torques. How should one model the 4 input motor voltages for the quadrotor as without these it seems the propulsion plugin does not do much?

echoing /motor_status shows

/motor_status
running: False
voltage: [0.0, 0.0, 0.0, 0.0]
frequency: [0.0, 0.0, 0.0, 0.0]
current: [0.0, 0.0, 0.0, 0.0]