20.4:1 Metal Gearmotor 25Dx65L mm LP 6V with 48 CPR Encoder

via Pololu
$44.37
SKU PL-4823
This gearmotor consists of a low-power, 6 V brushed DC motor combined with a 20.4:1 metal spur gearbox, and it has an integrated 48 CPR quadrature encoder on the motor shaft, which provides 979.62 counts per revolution of the gearbox’s output shaft. The gearmotor is cylindrical, with a diameter just under 25 mm, and the D-shaped output shaft is 4 mm in diameter and extends 12.5 mm from the face plate of the gearbox. This gearmotor is also available without an encoder.