Hi,
I want to model the motor in matlab and make a control system model. For that i need the following parameters:
J = system moment of inertia of the rotor
b = motor viscous friction
Ke = back-EMF constant
Kt = motor torque constant
R = armature winding resistance
L = armature winding inductance
V = armature winding input voltage
I = armature winding current

Here is a link to a forum post I wrote which outlines how to can do that. Please note, unlike the motor discussed in that forum post, the inductance of our 12V 37D motors is about 2.3mH. Also, for moment of inertia calculations, the output shaft on our 37D gearmotors is stainless steel.

% back-EMF constant(rated voltage[12V]/free-run speed with gearbox[330RPM])
Ke = 0.003636 % [Volts]

% motor torque constant without gearbox(stall torque[14Nm]/[stall current[5.5A] - free run current[0.2A]])
Kt = 2.64151 % [Nm/A]

% motor constant (torque constant[Kt]/square root of the armature resistance[R])
Km = 3.08176

% motor viscous friction ([no-load current[0.2]/no-load speed[330]]*motor torque constant[K_t])
b = 0.0016 % []

% armature winding inductance
L_arm = 2.3 % [mH]

% armature winding input voltage
V = ??? % [Votls]

% armature winding current
I = ??? % [Amper]

% system moment of inertia of the rotor [J = (pai/32)Density of S.SLength*Diameter^4 = (3.14/32)*7.75[Kg/mm^3]*16[mm]5.4[mm]^4]
J = 10,351.34 % [Kgmm^2]

The input voltage is not something you calculate; it is your input. The motor current is a function of the supply voltage and load as indicated by the performance curves in the datasheet.