56:1 Metal Gearmotor 20Dx42L mm

New versions available! We have replaced these older short-shaft versions of our 20D mm gearmotors with a much wider assortment of gear ratios that feature longer output shafts. You can find the full selection of these new versions here. The older versions are now only available by large-volume special order. Please contact us for more information.

Note that the following product page is being left here for historical purposes; it has not been updated to reflect our current offering of 20D mm gearmotors.

Overview

The 20D mm line of brushed DC gearmotors all have the same dimensions except for the length of the gearbox, and they 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. Higher voltages could start negatively affecting the life of the motor, and lower voltages might not be practical. Four different gear ratios are available:

Gear Ratio	No-Load Speed @ 6 V	No-Load Current @ 6 V	Stall Torque @ 6 V	Stall Current @ 6 V
29:1	450 RPM	250 mA	25 oz-in	3.2 A
56:1	250 RPM	250 mA	45 oz-in	3.2 A
73:1	180 RPM	250 mA	60 oz-in	3.2 A
154:1	90 RPM	250 mA	120 oz-in	3.2 A

Note: Stalling gearmotors can greatly decrease their lifetimes, occasionally resulting in immediate damage to the gearbox. This is especially true for the higher gear ratios, which can generate enough torque to damage themselves. Prolonged stalls (on the order of seconds) can result in thermal damage to the motor windings and brushes.

The gearmotor face plate has two mounting holes threaded for M2.5 screws, and you can use our custom-designed 20D mm metal gearmotor bracket (shown in the left picture below) to mount the gearmotor to your project via these mounting holes and the screws that come with the bracket.

Pololu 20D mm gearmotor with bracket and hub.

White Pololu Wheel 60×8mm on a Pololu 20D mm Metal Gearmotor.

This gearmotor has an output shaft with a diameter of 4 mm; the Pololu universal aluminum mounting hubs 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 right picture above). 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, and you can use our 12mm hex wheel adapter to use this motor with many common hobby RC wheels. The gearbox’s output shaft also works directly with the 120mm-diameter Wild Thumper wheels, as shown below.

Dagu Wild Thumper wheel 120×60mm (metallic red) with Pololu 20D mm metal gearmotor.

Dimension Diagram

The diagram below shows the dimensions of the 25D mm line of gearmotors (units are mm over [inches]). This diagram is also available as a downloadable PDF (172k pdf).

Dimensions of the original Pololu 20D mm metal gearmotors with shorter output shafts. Units are mm over [inches]. This diagram only applies to the listed gear ratios.

This diagram is also available as a downloadable PDF (172k pdf).

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.

People often buy this product together with:

Pololu Universal Aluminum Mounting Hub for 4mm Shaft, #4-40 Holes (2-Pack)

Pololu 20D mm Metal Gearmotor Bracket Pair

73:1 Metal Gearmotor 20Dx42L mm (Short Output Shaft)