is it possible to calculate gear reduction based on the datasheet of SG90 servo motor? Because I wanted to do some modeling in Simulink and RC servo ask for gear reduction, but I can't find any information about the gear reduction.
If it does not say directly in the data sheet, you can calculate it from:
the nominal speed of the DC motor vs. the nominal speed of the whole servo assembly (incl. gears).
the maximum torque of the DC motor vs. the maximum torque of the entire assembly (incl gears)
the velocity constant of the motor and the nominal voltage can be used to calculate the nominal speed of the dc-motor, after this see point 1.
the torque constant and the max current of the DC motor can be used to determine the maximum torue of the DC motor, after this see point 2.
the torque constant of the motor is specified, it equals (as value not as unit of measurment) the velocity constant of the dc motor, after this see point 3.
a detailed drawing is presented you can count the teeth on the gears and calculate the transmission ratio from those (and hope that the drawing matches the motor)
You can disassemble the servo nd count the teeth of the gears and compute the transmission ratio