19:1 Metal Gearmotor 37Dx68L mm 12V with 64 CPR Encoder (Helical Pinion)

by Pololu

This gearmotor is a powerful 12V brushed DC motor with a 18.75:1 metal gearbox and an integrated quadrature encoder that provides a resolution of 64 counts per revolution of the motor shaft, which corresponds to 1200 counts per revolution of the gearbox’s output shaft.

The gearbox is composed mainly of spur gears, but it features helical gears for the first stage for reduced noise and improved efficiency. These units have a 16 mm-long, 6 mm-diameter D-shaped output shaft.

Measuring 37 mm (1.46″) in diameter, these brushed DC gearmotors are the largest and most powerful we carry. 


Size: 37D × 68L mm(1)
Weight: 200 g
Shaft diameter: 6 mm(2)
Gear ratio: 18.75:1
No-load speed @ 12V: 530 rpm
No-load current @ 12V: 0.2 A
Stall current @ 12V: 5.5 A(3)
Stall torque @ 12V: 8.5 kg/cm(3)
Max output power @ 12V: 12 W
No-load speed @ 6V: 270 rpm(4)
No-load current @ 6V: 0.15 A(4)
Stall current @ 6V: 3.0 A(4)
Stall torque @ 6V: 5.0 kg/cm(4)
Motor type: 12V

Performance at maximum efficiency

Max efficiency @ 12V: 55 %
Speed at max efficiency: 470 rpm
Torque at max efficiency: 1.0 kg·cm
Current at max efficiency: 0.76 A
Output power at max efficiency: 5.0 W

1 Length measurement is from gearbox face plate to back of encoder cap (it does not include the output shaft). See dimension diagram for details.
2 D shaft.
3 Stalling is likely to damage the gearmotor. Stall parameters come from a theoretical extrapolation of performance at loads far from stall. As the motor heats up, as happens as it approaches an actual stall, the stall torque and current decrease.
4 This motor will run at 6 V but is intended for operation at 12 V.
5 May vary by a few centimeters.

Note: The listed stall torques and currents are theoretical extrapolations; units will typically stall well before these points as the motors heat up. Stalling or overloading gearmotors can greatly decrease their lifetimes and even result in immediate damage. The recommended upper limit for continuously applied loads is 10 kg-cm (150 oz-in), and the recommended upper limit for instantaneous torque is 25 kg-cm (350 oz-in). Stalls can also result in rapid (potentially on the order of seconds) thermal damage to the motor windings and brushes; a general recommendation for brushed DC motor operation is 25% or less of the stall current.

In general, these kinds of motors can run at voltages above and below the nominal voltages; lower voltages might not be practical, and higher voltages could start negatively affecting the life of the motor.

Using the Encoder

A two-channel Hall effect encoder is used to sense the rotation of a magnetic disk on a rear protrusion of the motor shaft. The quadrature encoder provides a resolution of 64 counts per revolution of the motor shaft when counting both edges of both channels. To compute the counts per revolution of the gearbox output, multiply the gear ratio by 64. The motor/encoder has six color-coded, 8″ (20 cm) leads terminated by a 1×6 female header with a 0.1″ pitch, as shown in the main product picture. The following table describes the wire functions:

Colour Function
Red motor power (connects to one motor terminal)
Black motor power (connects to the other motor terminal)
Green encoder GND
Blue encoder Vcc (3.5 – 20 V)
Yellow encoder A output
White encoder B output

The Hall sensor requires an input voltage, Vcc, between 3.5 and 20 V and draws a maximum of 10 mA. The A and B outputs are square waves from 0 V to Vcc approximately 90° out of phase. The frequency of the transitions tells you the speed of the motor, and the order of the transitions tells you the direction. The following oscilloscope capture shows the A and B (yellow and white) encoder outputs using a 12 V motor at 12 V and a Hall sensor Vcc of 5 V:

By counting both the rising and falling edges of both the A and B outputs, it is possible to get 64 counts per revolution of the motor shaft. Using just a single edge of one channel results in 16 counts per revolution of the motor shaft, so the frequency of the A output in the above oscilloscope capture is 16 times the motor rotation frequency.