Pololu 25:1 Metal Gearmotor 20Dx41L mm 12V CB

These small brushed DC gearmotors can deliver a lot of power for their size. This version has a 12V brushed DC motor with long-life carbon brushes combined with a 25:1 metal spur gearbox. The gearmotor is cylindrical with a diameter of 20 mm, and the D-shaped output shaft is 4 mm in diameter and extends 18 mm from the face plate of the gearbox. Key specs at 12 V: 570 RPM and 90 mA with no-load, 26 oz-in (1.9 kg-cm) and 1.6 A at stall.