Description

Overview

These cylindrical brushed DC gearmotors are available in a wide range of gear ratios and with five different motors (two power levels of 6 V motors and three power levels of 12 V motors). The gearmotors all have the same 25 mm diameter case and 4 mm diameter gearbox output shaft, so it is generally easy to swap one version for another if your design requirements change (though the length of the gearbox tends to increase with the gear ratio). The motor and encoder portion is available by itself (no gearbox) for each combination of power level and nominal operating voltage, and versions without the encoder are also available. Please see the 25D metal gearmotor comparison table for detailed specifications of all our 25D metal gearmotors. This dynamically-sortable table can help you find the version that offers the best combination of speed, torque, and current draw for your particular application. 

Note: Stalling or overloading gearmotors can greatly decrease their lifetimes and even result in immediate damage. For these gearboxes, the recommended upper limit for instantaneous torque is 15 kg-cm (200 oz-in); we strongly advise keeping applied loads well under this limit. Stalls can also result in rapid (potentially on the order of a second) thermal damage to the motor windings and brushes, especially for the versions that use high-power (HP) motors; 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 their nominal voltages (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 little bit of base plastic that will remain, as shown in the picture below:

Details for item #4847

Warning: Do not screw too far into the mounting holes as the screws can hit the gears. We recommend screwing no further than 6 mm (0.24″) into the screw hole.

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, 8″ (20 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:

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.

Gearmotor accessories

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.

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.

Dimensions

Size:	25D x 69L mm1
Weight:	104 g
Shaft diameter:	4 mm

General specifications

Gear ratio:	98.78:1
No-load speed @ 12V:	100 rpm
No-load current @ 12V:	300 mA
Stall current @ 12V:	5600 mA
Stall torque @ 12V:	300 oz·in2
No-load speed @ 6V:	50 rpm3
Stall current @ 6V:	2800 mA3
Stall torque @ 6V:	150 oz·in3
Motor type:	5.6A stall @ 12V (HP 12V)
Lead length:	8 in4
Encoders?:	Y

Notes:

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

This is a theoretical value; stalling the gearbox output shaft is likely to damage the gearbox.

3

This motor will run at 6 V but is intended for operation at 12 V.

4

May vary by a few inches.

Resources

File downloads

• Dimension diagram of the Pololu 25D Metal Gearmotors (171k pdf)

• 3D models of 25D mm gearmotors (10MB zip)

  This file contains 3D models (in the step file format) of the 25D mm gearmotors with and without encoders.

• Modifying the Wild Thumper to use motors with encoders (3MB pdf)

  Customer Richard Nguyen has documented his work modifying the Wild Thumper chassis to use 25D motors with encoders in place of the chassis’s included motors.

  Note: This is not an easy modification, and the chassis can be damaged if it is not done properly, so we generally recommend against it, and we can only provide very limited support for those who want to attempt it. The manufacturer did not intend for the chassis to be modified in this way, and we do not know how well such a modification will work out.

Recommended links

• MATLAB script to plot motor performance curves for Pololu brushed DC gearmotors

  This MATLAB script, written by Ali Asgher Mansoor Habiby, plots speed, power, current draw, and efficiency as they vary with torque when you input the gearmotor specifications. It also prints the resistance of the motor, and the current draw and torque at which maximum efficiency and maximum power occur.