In DC motors gears are used :
to decrease (sometimes, increase) the rotational speed of the shaft
to increase the torque of the motor
for inertia matching between motor and load
(in some applications such as Robotic Arm, etc.) to get Standstill torque
There are three methods of controlling the speed of DC geared motor..
Armature resistance control: By controlling the armature resistance we can control the voltage drop across it thus controls the induced EMF across the armature and by varying the EMF shaft speed can be controlled because Eb = K× N.
Field flux controlling: By controlling the field voltage we can control the EMF induced across the armature and thus control the speed of the motor shaft…
Supply voltage controlling: I think you get the point…
