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How can I get the value of B for a DC motor when the data sheet has Viscous Damping (F1) like the following?

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The 'Mechanic' block stands for the mechanical part of the system, which is described by the Newton's second law for rotation: $$ J\dot \omega=\tau, $$ where tau is the overall torque. If we split it into the torque of viscous friction and the external torque, we get $$ J\dot \omega=\tau_{ext}-B \omega $$ or $$ J\dot \omega+B \omega=\tau_{ext}, $$ where B is a viscous damping coefficient. Computing the Laplace transforms gives us $$ (Js+B)\Omega= T_{ext} $$ or $$ \Omega=\frac1{Js+B} T_{ext}. $$ Thus, B from the 'mechanic' block is nothing but a viscous damping coefficient.

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