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131:1 Gearmotor 64 CPR Encoder

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$34.95 ea

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  • Jameco Part no.: 2238101
  • Manufacturer: Pololu
  • Manufacturer no.: 2827
  • Electronics Parts Locator
  • This item is discontinued and is not
    recommended for new designs.
# of units Price
1+ $34.95
5+ $32.95
25+ $29.95

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131:1 12V Metal Gearmotor with 64 CPR Encoder 37Dx73L mm

This gearmotor is a powerful 12V brushed DC motor with a 131.25:1 metal gearbox and an integrated quadrature encoder that provides a resolution of 64 counts per revolution of the motor shaft, which corresponds to 8400 counts per revolution of the gearbox's output shaft. These units have a 0.61" long, 6 mm diameter D-shaped output shaft.

These motors are intended for use at 12 V, though these kinds of motors can run at voltages above and below the nominal voltage (they can begin rotating at voltages as low as 1 V). Lower voltages might not be practical, and higher voltages could start negatively affecting the life of the motor.

These gearmotors are functionally identical to the previous versions we carried without end caps (they use the same motor, encoder, and gearboxes). The black plastic end cap is easily removable if you need to access the encoder or want to slightly reduce the overall gearmotor size, but there is a small amount of base plastic that will remain, as shown in the pictures below:

View of encoder on gearmotor


  • Gear ratio: 131:1
  • No-load Speed @ 12V: 80 RPM
  • Stall Torque @ 12V: 250 oz-in
  • Stall Current @ 12V: 5 A
  • Size: 37 mm diameter x 73 mm long
  • Shaft Diameter: 6 mm D-shaft
  • Lead Length: 11"

Note: Stalling or overloading gearmotors can greatly decrease their lifetimes and even result in immediate damage. 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.

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, 11" (28 cm) leads terminated by a 1x6 female header with a 0.1" pitch, as shown in the main product picture. This header works with standard 0.1" male headers and our male jumper and pre-crimped wires. If this header is not convenient for your application, you can pull the crimped wires out of the header or cut the header off. The following describes the wire functions:

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. By counting both the rising and falling edges of both the A and B outputs, it's 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.

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Specification Value
Voltage Rating12 VDC
Motor Speed @ Max. Efficiency (RPM)80
Current @ Max. Efficiency (mA)250
Torque @ Max. Efficiency (g-cm)18000
Gear Ratio131:1
Gear Case Size (Diameter x Length) (inch)2.7 x 1.45
Motor Size (Diameter x Length) (inch)1.3 x .63
Shaft Size (Diameter x Length) (inch)0.24 x 0.60 (flat side)

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