I find the unit of damping coefficient referenced from http://gazebosim.org/tutorials/?tut=ros_urdf#Joints and viscous friction coefficient in the motor which is usually expressed as Bm is (N*m)/(rad/s), so are they the same physical quantity? I want to simulate a servo motor, what value should the damping coefficient be?

If the damping coefficient = c and angular velocity = w, the damping force is c*w?