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I would like to know how to calculate or select DC motor parameters when knows some parameters.
Knowing parameters:
How to calculate or select following parameters?
It is not clear if you are trying to design a motor or select one. The friction torque seems a little high for bearing friction, but quite low for a load unless you are just accelerating inertia and overcoming aerodynamic drag.
80 N-m at 2000 RPM is 17 kW. If the motor has an efficiency of 80%, you will need about 21 kW of electrical power. At 48 volts, you would need 440 amps. That is not a very convenient current level to work with. The first thing you need to do is decide what voltage and current levels you want to work with. Then you can determine the motor constant as described in another answer.
Given a speed/torque requirement, you're going to want to pick a motor out based on K, the maximum rated voltage, and the maximum rated current/stall current. The equations you care about:
Max motor speed (in rpm, steady state, no load): $$\dot{\theta}_{max} = V_{max}K $$
Max motor torque (in Nm): $$ \tau_{max} = I_{max} \frac{60}{2\pi K} $$
The friction torque and load inertia are both only relevant to the torque specification of your motor. Also note that you'll probably need a small (possibly single stage) gear reduction to hit your speed/torque requirements, and a 10s of kW motor controller (~20kW). Sounds like a motor you might find in an electric bike or low power electric motorcycle.
