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131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder


This powerful brushed DC gearmotor features an integrated quadrature encoder with 64 counts per revolution (CPR) of the motor shaft. it is intended for use at 12 V, though in general, this kind of motor can run at voltages above and below the nominal voltage (it 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.

The face plate has six mounting holes evenly spaced around the outer edge threaded for M3 screws (not included).These mounting holes form a regular hexagon and the centers of neighboring holes are 15.5 mm apart. 

The 6 mm diameter gearbox output shaft works with the universal aluminum mounting hub for 6mm shafts, which can be used to mount larger wheels (90mm-diameter) or custom wheels and mechanisms to the gearmotor’s output shaft . 

Warning: Do not screw too far into the mounting holes as the screws can hit the gears. it is recommended screwing no further than 3mm (1/8") into the screw hole. 


Gear ratio:131:1

  • Free-run speed @ 6V: 40 rpm.
  • Free-run current @ 6V: 250 mA.
  • Stall current @ 6V: 2500 mA.
  • Stall torque @ 6V: 9
  • Free-run speed @ 12V: 80 rpm.
  • Free-run current @ 12V: 300 mA.
  • Stall current @ 12V: 5000 mA.
  • Stall torque @ 12V: 18
  • Lead length:27.94 in.
  • encoder counts per revolution (CPR): 64 CPR. 
  • Size: 37D x 69L mm.
  • Weight: 216g.
  • Shaft diameter: 6 mm.

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 1×6 female header with a 0.1″ pitch, as shown in the main product picture. This header works with standard 0.1″ male headers. 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 table describes the wire functions:

encoder wires

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 motor voltage of 12 V and a Hall sensor Vcc of 5 V:

Encoder A and B outputs for 37D mm metal gearmotor with 64 CPR encoder (motor running at 12 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.


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