These DC motors include gear container and encoder. It uses 2 phase or 2 
stations (quadrature) incremental encoders to identify the velocity of the motor, direction of rotation and the distance it has travelled.
Encoder feedback data enables you to control your motor speed and direction efficiently. DC motors with encoder feed back signal usually known as DC servo motors.
DC motors with encoder have many applications in robots, robot arm, CNC machine and several other applications that require accurate control of rate, direction and position. You can control your motor using microcontroller or Drive Chain arduino.
DC Motor Specifications
Voltage: 6:12 VDC
Output Power: 2.2 W
Gear Ratio: 1:75
Rated Speed: 133 RPM
Ranked Torque: 25.4 N.cm
Stall Current: 3A
Encoder Type: Hall effect quadrature encoder 5v (monitor position and path of rotation)
Size: 25 x 54 mm
Weight: 120 g
Shaft Diameter: 4mm