120:1 Mini Plastic Gearmotor, 90° 2mm Spline Output

This compact, inexpensive, low-current gearmotor (brushed DC motor with a 120:1 reduction gearbox) is well suited for use in small robots.

Not currently available

Our Code: SKU-002504

Supplier Link: [Pololu MPN:1123]


Description

Pololu mini plastic gearmotor 90 deg. output with opened gearbox

Overview

This brushed DC gearmotor is very compact and weighs only 0.7 ounces (19.5 grams) — perfect for building a quick, miniature robot. The recommended operating voltage range for this motor is 3 to 6 V, though the gearmotor can start rotating at voltages as low as 0.6 V. At 4.5 V, the motor has a free-run current of 80 mA and a stall current of 800 mA; this relatively low current draw makes this a great match for our qik 2s9v1 dual serial motor controller and programmable Orangutan robot controllers. The stall current, torque, and rotation speed will approximately scale linearly with the motor voltage. The gearbox is protected by a built-in safety clutch that will typically slip before gear teeth can shear.

Dimensions

Dimension diagram of the mini plastic gearmotor with 90° 2mm spline output (units are mm over [in])

This dimension diagram is also available as a downloadable pdf (75k pdf).

This gearmotor features a splined, chrome-finish output shaft with a 2mm-crest diameter. This shaft can be used with custom wheels or with our adaptor for LEGO wheels. The gearbox output shaft is perpendicular to the motor shaft.

Gearmotor Versions

We carry two versions of mini plastic gearmotors with 2 mm diameter spline output shafts, one with an offset shaft and one with a 90° shaft.

We have many more versions of these mini plastic gearmotors available with 3 mm diameter “D”-shaped output shafts (just like the ones on our micro metal gearmotors) that are compatible with many Pololu wheels and our 3 mm universal mounting hubs. These versions offer two output shaft orientations relative to the motor shaft (offset and 90°), two motor options (normal and high-power, or HP for short), and two gearbox options (120:1 and 180:1). Additionally, some of these versions are available with an extended motor shaft that protrudes from the rear of the motor by approximately 4.5 mm. This second shaft has a diameter of 1.5 mm and rotates at the same speed as the input to the gearbox, offering a way to add a custom-built encoder to provide motor speed or position feedback. The following table shows all of the mini plastic gearmotors that have 3 mm D-shafts:

Motor Type Stall
Current
@ 4.5 V
No-Load
Speed
@ 4.5 V
Stall Torque
@ 4.5 V


90° output


90° output + motor shaft


offset output


offset output + motor shaft
high-power
(HP)
1250 mA 150 RPM 25 oz-in 120:1 mini HP 120:1 mini HP 120:1 mini HP 120:1 mini HP
low-power 800 mA 120 RPM 20 oz-in 120:1 mini 120:1 mini 120:1 mini 120:1 mini
80 RPM 30 oz-in 180:1 mini 180:1 mini

Note: The stall torque values listed are approximate, and the built-in safety clutch might start slipping at lower torques.


Specifications

Dimensions

Size: 54.5 x 20 x 13.8 mm1
Weight: 19 g
Shaft diameter: 2 mm2

General specifications

Shaft type: 90° 2mm spline
Typical operating voltage: 4.5 V
Gear ratio: 120:1
Free-run speed @ 4.5V: 120 rpm
Free-run current @ 4.5V: 80 mA
Stall current @ 4.5V: 800 mA
Stall torque @ 4.5V: 20 oz·in3
Extended motor shaft?: N

Notes:

1
See drawing for detailed dimensions.
2
Measurement is diameter of spline crest.
3
Note: the gearbox's built-in clutch might start slipping at a lower torque.

Resources

File downloads

dimension diagram: 90° 2mm spline version (75k pdf)
Dimension diagram of the mini plastic gearmotor with 90° 2mm spline output.

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.

FAQs

I need additional information about this motor; do you have a datasheet?

No; the information we have available for this motor can be found on its product page. However, you can approximate various additional motor parameters from the information found in the “Specs” tab.

The electrical resistance of the motor can be approximated by dividing the rated voltage by the stall current (at the rated voltage). The electromotive force constant (Ke) can be approximated by dividing the rated voltage by the free-run speed (at the rated voltage). To approximate the motor torque constant (Kt), you can divide the stall torque by the stall current.

For pretty much any DC motor, the current, speed, power, and efficiency curves as a function of torque will look like those in the graph below (assuming motor voltage and temperature are constant):

The current and speed curves are approximately linear, and the product pages for our motors provide the approximate end points for these lines: (0 torque, no-load current) and (stall torque, stall current) for the red line, and (0 torque, no-load speed) and (stall torque, 0 speed) for the blue line.

The orange output power curve is the product of the speed and the torque, which results in an inverted parabola with its peak at 50% of the stall torque.

The green efficiency curve is the output power divided by the input power, where the input power is current times voltage. The voltage is constant, so you can divide the output power curve by the current line to get the general shape of the efficiency curve, which in turn lets you identify the torque, speed, and current that correspond to max efficiency.

There are many programs out there that you can use to generate these curves. For example, if you have access to MATLAB, you can use this customer-created MATLAB script to generate these motor plots for you from the specifications we provide for each gearmotor.

Note: A good general rule of thumb is to keep the continuous load on a DC motor from exceeding approximately 20% to 30% of the stall torque. Stalling gearmotors can greatly decrease their lifetimes, occasionally resulting in immediate damage to the gearbox or thermal damage to the motor windings or brushes. Do not expect to be able to safely operate a brushed DC gearmotor all the way to stall. The safe operating range will depend on the specifics of the gearmotor itself.