This is a DFRobot customised high quality DC motor. The best part of this motor is that it is a quiet and high torque output motor with optical encoder built in. The optical encoder gives 663 pulses per rotation which is able to sense 0.54 degree rotation from the shaft. The resolution can meet general PID speed control requirements.
This motor is widely used in mobile robotics.
Note: A pull-up resistor between VCC & signal is necessary when using encoders.