The 1119-POLOLU is a great low cost alternative to modified hobby servos for building quick small robots. 

The recommended operating voltage range for this motor is 3 to 12 V. At 6 V, it has a free-run speed of 85 RPM and a stall torque of approximately 65 oz-in. The motor at 6V has a free-run current of 70 mA and a stall current of 800 mA. The stall current, torque, and rotation speed will approximately scale linearly with the motor voltage. The gearbox is protected by a built-in safety clutch that will typically slip before gear teeth can shear.  There are built-in mounting holes, and the output shaft is 6 mm long and 7 mm in diameter with two sides flattened.

Features:

• 90° output shaft
• Typical operating voltage: 6V
• Gear ratio: 120:1
• Free-run speed/current @ 6V: 85 rpm/70 mA
• Stall current/torque @ 6V: 800 mA/65 oz·in