These gear motors are made with steel gears (not plastic or sintered metal).  They run great and we've tested them extensively on our All-Terrain-Robots and Vectoring Robots.  We sampled many other manufactures and the gears would strip or the windings would burn up, we had no failures with these.

These gear motors have encoders mounted to the tail shaft of the motor.  They are hall effect encoders that count the revolutions the motors make.  Since its a two channel encoder you can detect the direction of rotation and pick up 4 rises and falls per revolution of the motor.  Apply the gear ratio of the motor and any further reduction of your drive train to get total revolutions of your wheel, etc.  Follow this link for a datasheet for the encoder.

We recommend controlling the motors with one of our motor speed controllers. See our motor controller support page for more information.  We also recommend you use our wiring kit to wire your motors to control the electronic noise generated from any DC motor.  See our motor wiring support page for more information. 

The table below lists its characteristics.  The images above show current and torque curves and dimensions.  These motors have a stall torque of  60 kgf-cm!  They utilize a 1:84 gear reduction.  The gear motor is 24VDC.