34:1 Metal Gearmotor 25Dx52L mm HP with 48 CPR Encoder
 

This cylindrical, 2.54" x 0.98" x 0.98" gearmotor uses a brushed
DC motor with extra-strong magnets and a 34.014:1 metal gearbox to deliver a lot of power in a relatively small package.
It has an integrated 48 CPR quadrature encoder on the motor shaft,
which provides 1633 counts per revolution of the gearbox’s output shaft.
These units have a 0.315"-long, 4 mm-diameter D-shaped output shaft. We also carry
a lower-power version of this gearmotor and a version without an encoder.

Key specs at 6 V: 285 RPM and 450 mA free-run, 60 oz-in (4.3 kg-cm) and 6 A stall.

These motors are intended for use at 6 V. In general, these kinds of motors
can run at voltages above and below this nominal voltage,
so they should comfortably operate in the 3 – 9 V range, though they can begin rotating at voltages as low as 1 V.
Higher voltages could start negatively affecting the life of the motor.

These gearmotors have output shafts with a diameter of 4 mm.
The Pololu universal aluminum mounting hub for 4mm shafts can be used to mount our larger Pololu wheels
(60mm-, 70mm-, 80mm-, and 90mm-diameter) or custom wheels and mechanisms to the gearmotor’s output shaft
(see the left picture below).
These are the same type of motors used in the Wild Thumper all-terrain chassis,
and the gearbox’s output shaft works directly with the 120mm-diameter Wild Thumper wheels.
 

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 48 counts per revolution of the motor shaft.
To compute the counts per revolution of the gearbox output, multiply the gear ratio by 48.
The motor/encoder has six color-coded, 11" (28 cm) leads:

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 6 V and a Hall sensor Vcc of 5 V:
 

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