# Urgent Help needed for Motor Calculation

I have a 131:1 Metal Gearmotor 37Dx57L mm motor.

I am trying to calculate Ke, Kt and resistance of the motor.

The specifications is given by:
|Gear ratio:|131:1|
|Free-run speed @ 12V:|80 rpm|
|Free-run current @ 12V:|300 mA|
|Stall current @ 12V:|5000 mA|
|Stall torque @ 12V:|250 oz·in|

According to the FAQ it is stated that, “The electrical resistance of the motor can be approximated by dividing the rated voltage by the stall current (at the rated voltage). The electromotive force constant (Ke) can be approximated by dividing the rated voltage by the free-run speed (at the rated voltage). To approximate the motor torque constant (Kt), you can divide the stall torque by the stall current.”.

electrical resistance of the motor = 12v/5A = 2.4
electromotive force constant (Ke)= 12V/80RPM = 0.15
motor torque constant (Kt) = 1.765Nm/5A = 0.35308

I would like to ask if my caluclation is correct? Next i would like to ask do I need to take into consideration of the gear ratio 131.25 for the calculations of Ke and Kt? Is it okay if I don’t take in the gear ratio of 131.25?

for example: Ke = = 12V/(80rpm*131.25)

Hello.

Your calculations look correct (though you forgot the units). The values you calculated apply to the gearmotor as a whole. You only need to take into account the gearbox if you plan on using the motor without the gearbox.

Grant