Motor with 20 mm diameter and 43 mm length, 63:1 metal gear, 6 V operating voltage, 0.15 A to 2.9 A power consumption, 230 RPM speed and 4 kg*cm maximum torque. Pololu 3714

Motor with 20 mm diameter and 44 mm length, 156:1 metal gear, 6 V operating voltage, 0.15 A to 2.9 A power consumption, 91 RPM speed and 7.9 kg*cm maximum torque. Pololu 3718

Motor with 20 mm diameter and 46 mm length, 313:1 metal gear, 6 V operating voltage, 0.15 A to 2.9 A power consumption, 45 RPM speed and 13 kg*cm maximum torque. Pololu 3721

Motor with 20 mm diameter and 44 mm length, 156:1 metal gear, 6 V operating voltage, 0.15 A to 2.9 A power consumption, 91 RPM speed and 7.9 kg*cm maximum torque. Pololu 3456

A high-power miniature Pololu from the HP series. The motor with gear 210:1, shaft speed is 150rpm, torque is 3kg*cm (0.3Nm). The motor has an extended shaft which makes it easy to attach the encoder. Pololu 2216

Motor with 20 mm diameter and 41 mm length, 25:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 550 RPM speed and 1.9 kg*cm maximum torque. Pololu 3474

Motor with 20 mm diameter and 41 mm length, 31:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 450 RPM speed and 2.4 kg*cm maximum torque. Pololu 3475

Motor with 20 mm diameter and 43 mm length, 63:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 220 RPM speed and 4.6 kg*cm maximum torque. Pololu 3476

Motor with 20 mm diameter and 43 mm length, 78:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 180 RPM speed and 5.4 kg*cm maximum torque. Pololu 3477

Motor with 20 mm diameter and 44 mm length, 100:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 140 RPM speed and 6.1 kg*cm maximum torque. Pololu 3478

Motor with 20 mm diameter and 44 mm length, 125:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 110 RPM speed and 7.8 kg*cm maximum torque. Pololu 3479

Motor with 20 mm diameter and 44 mm length, 156:1 metal gear, 12 V operating voltage, 0.08 A to 1.6 A power consumption, 89 RPM speed and 9 kg*cm maximum torque. Pololu 3480