# 30:1 Metal Gearmotor 37Dx68L mm 12V with 64 CPR Encoder parameters

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

Hello.

Many of the parameters you are interested in can be derived from the performance curves in our 37D gearmotor datasheet, which is available on the product page under the “Resources” tab.

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.

- Patrick

Thank you so much Patric.

Can you help me with calculating/finding the armature winding input voltage and the armature winding current? Are they the No-Load V and A?

I will be happy to share with you my calculation, please let me know if something looks strange to you.

% armature winding resistance (rated voltage[12V]/Stall torque[14Nm])
R = 0.857143 % [Oham]

% 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

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 % [Kg
mm^2]

Thanks!

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.

- Patrick