I am trying to study/learn mathematical modelling of a DC motor i came across an equation which is known as the mechanical equation for an armature-controlled DC motor

I have understood other parameters in this equation but i am confused by the highlighted "b" term , what is meant by it?

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1 Answer 1


The b represent the drag/viscous coefficient of the motor


2.2 The mechanical equations Let us now deal with the mechanical representation of the motor. It has been shown in Section 1.2 that the motor exerts a torque, while supplied by voltages on the stator and on the rotor. This torque acts on the mechanical structure, which is characterized by the rotor inertia J and the viscous friction coefficient F. It has also to be taken into account that


Viscous damping in BLDC

DC motor differential equation

  • \$\begingroup\$ is ''b'' the same thing viscous friction coefficient"F" ?? \$\endgroup\$
    – DSP_CS
    Commented Aug 29, 2019 at 11:36
  • 1
    \$\begingroup\$ Yes it is. If you look at the placement of the variable and the intent of the equation it is producing the same effect: subtraction of a torque which is proportional to rotor velocity \$\endgroup\$
    – user16222
    Commented Aug 29, 2019 at 11:39

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