This brushed DC gearmotor is available in high- and low-power versions in a number of gear ratios. The motor and encoder portions are available by themselves (i.e. without the gearbox), and many other gear ratios are also available without an encoder.
Note: At some of the higher gear ratios, these motors can generate enough torque to damage themselves. Any torque greater than about 250 oz-in (18 kg-cm) is likely to damage the gearbox, so we recommend that you avoid stalling the 172:1 HP, 227:1, 378:1, and 499:1 versions of these motors at 6 V.
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.
Details for item #2288
Exact gear ratio: ``(22×20×22×22×22×22×24) / (12×12×10×10×10×10×10) ~~ bb(171.79:1)``
The face plate has two mounting holes threaded for M3 screws. You can use our custom-designed 25D mm metal gearmotor bracket (shown in the picture below) to mount the gearmotor to your project via these mounting holes and the screws that come with the bracket.
|Pololu 25D mm metal gearmotor bracket pair.||
|Pololu 25D mm gearmotor with bracket.|
The 4 mm diameter gearbox output shaft works with Pololu universal aluminum mounting hub for 4mm shafts, which 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 as shown in the left picture below. Alternatively, you could use our 4mm scooter wheel adapter to mount many common scooter, skateboard, and inline skate wheels to the gearmotor’s output shaft as shown in the right picture below.
|25D mm metal gear motor with 48 CPR encoder and Pololu 60×8mm wheel.||
|A 25D mm gearmotor connected to a scooter wheel by the 4 mm scooter wheel adapter.|
These are the same type of motors used in the Wild Thumper all-terrain chassis, so the gearbox’s output shaft also works directly with the hex adapters included with the 120mm-diameter Wild Thumper wheels (the left picture below shows a 25D mm gearmotor while the right picture shows the smaller 20D mm gearmotor):
|Dagu Wild Thumper wheel 120×60mm (chrome) with Pololu 25D mm metal gearmotor.||
|Dagu Wild Thumper wheel 120×60mm (metallic red) with Pololu 20D mm metal gearmotor.|
For a general-purpose hex adapter, consider our 12mm hex wheel adapter
, which lets you use this motor with many common hobby RC wheels.
|12mm Hex Wheel Adapter for 4mm Shaft on a 20D mm Metal Gearmotor.|
The diagram below shows the dimensions (in mm) of the 25D mm line of gearmotors. Note that the encoder PCB and magnetic disc are not shown in this dimension diagram; the encoder assembly extends an additional 12 mm beyond the rear of the motor. The value of
L is shown in the table below.
|Dimension diagram (in mm) for the 25D mm metal gearmotors.||
|25D mm metal gearmotor with 48 CPR encoder: close-up view of encoder.|
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 when counting both edges of both channels. 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 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 and our male jumper and precrimped 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 table describes the wire functions:
||motor power (connects to one motor terminal)
||motor power (connects to the other motor terminal)
||encoder Vcc (3.5 – 20 V)
||encoder A output
||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 6 V and a Hall sensor Vcc of 5 V:
|Encoder A and B outputs for 25D mm HP metal gearmotor with 48 CPR encoder (motor running at 6 V).|
By counting both the rising and falling edges of both the A and B outputs, it is possible to get 48 counts per revolution of the motor shaft. Using just a single edge of one channel results in 12 counts per revolution of the motor shaft, so the frequency of the A output in the above oscilloscope capture is 12 times the motor rotation frequency.
Selecting the Right Gearmotor
We offer a wide selection of metal gearmotors that offer different combinations of speed and torque. Our metal gearmotor comparison table can help you find the motor that best meets your project’s requirements.
|Some of the Pololu metal gearmotors.|
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