120:1 Mini Plastic Gearmotor, Offset 3mm D-Shaft Output, Extended Motor ShaftPololu
This compact, inexpensive plastic gearmotor (brushed DC motor with a 120:1 reduction gearbox) is well suited for use in small robots. While intended for operation at 4.5 V, it should run comfortably in the 3 V to 6 V range. The gearbox has a 9.7mm-long, 3 mm-diameter D-shaped output shaft that is perpendicular to the motor shaft, and a built-in safety clutch helps protect the gears from excessive loads. This version also has a 5×1.5 mm extended motor shaft.
Key specs at 4.5 V: 120 RPM and 80 mA free-run, 20 oz-in (1.4 kg-cm) and 0.8 A stall.
Option: offset 3mm D, 120 rpm, extended motor shaft