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3321_0 - 28STH32 NEMA-11 Bipolar Stepper with 27:1 Gearbox, 3321


This NEMA-11 motor has an integrated Planetary gearbox with a 26103/121 :1 ratio. It comes with the rear shaft exposed, so you can mount an encoder or shaft coupler.


When connected to a 1067 - PhidgetStepper Bipolar HC, the 3321 has a maximum speed of approximately 120 RPM.  At the output of the gearbox, the step angle approximately 0.067°. When using the step angle in calculations, you should derive the exact step angle by dividing 1.8° by the gearbox reduction ratio.

The 3321 stepper motor connects to a bipolar motor controller such as the 1067 - PhidgetStepper Bipolar HC.

The following diagram shows how to connect the motor wires to the board connectors to produce a clockwise rotation in the stepper motor when increasing position. To wire for counter-clockwise rotation when increasing position, reverse the red and blue wires.

Note: Make sure to unplug the power cord from the motor controller before switching wires around. The rear shaft of this motor can be equipped with the HKT22 Optical Encoder for applications where you need to keep track of the exact position, velocity, or acceleration of the motor.

The mounting holes on this motor are compatible with the 3337 - Mounting Bracket (NEMA11).

Product Specifications

Motor Properties

Motor Type

Bipolar Stepper

Manufacturer Part Number

28STH32-0674B / 28JXS40K27

Step Angle


Step Accuracy

± 5 %

Holding Torque

16.1 kg·cm

Rated Torque

14 kg·cm

Maximum Motor Speed

50 RPM

Electrical Properties

Recommended Voltage

24 V DC

Rated Current

670 mA

Coil Resistance

5.6 Ω

Phase Inductance

3.4 mH

Physical Properties

Shaft Diameter

6 mm

Rear Shaft Diameter

3.9 mm

Mounting Plate Size

NEMA - 11


217.5 g

Number of Leads


Wire Length

300 mm

Gearbox Properties

Gearbox Type


Gear Ratio

26 103121 : 1

Backlash Error


Maximum Strength of Gears

20 kg·cm

Shaft Maximum Axial Load

25 N

Shaft Maximum Radial Load

35 N