# Finding viscous damping coefficient and Static friction constant of BLDC motor

I have a BLDC motor and I know its Torque-Speed curve along with torque constant $$K_t$$, motor winding resistance $$R$$, and back emf constant $$K_e$$. I would like to determine its viscous damping coefficient and static friction constant. I found some different formulae to find the damping coefficient on the internet.

1. Damping coefficient: $$K_v = \frac{\Delta torque}{\Delta speed}$$
2. Mechanical time constant: $$\tau = \frac{R.J}{K_e.K_t}$$, where $$J$$ is rotor inertia. And then damping coefficient can be found by $$K_v = \frac{J}{\tau} \implies \frac{K_t.K_e}{R}$$

From 1. I infer that the damping coefficient is equal to the slope of torque-speed curve, Please correct me if I am wrong. But this slope is negative and I found that damping coefficients are positive.

From 2. I can find $$K_v$$ but it is different from 1.

My question is which one of the above methods is correct and if there are some other ways to find these constants. Also is there any good way to find the static friction constant from the above parameters?