20J1840-404 NEMA8 Stepper Motor - 40 mm, 0.027 N·m

The 20J1840-404 is a NEMA8 Stepper Motor in the 20 mm micro frame, 40 mm long, rated 0.027 N·m at 0.4 A with a 4 mm shaft. It is designed for the very compact mechanisms found in laboratory instruments and precision positioning systems, where every millimetre of envelope is allocated early in the design.

Micro Torque for Precision Positioning

The 0.027 N·m rating safely moves optics adjusters, particle positioning fixtures, and minute specimen stages. The low 0.4 A current is easily supplied by compact driver boards and small power supplies, which makes the motor attractive for portable and battery-operated instruments. Its open-loop stepping gives repeatable movement without encoder complexity.

Specification

• Frame: NEMA8 (20 mm)
• Body length: 40 mm
• Phase current: 0.4 A
• Holding torque: 0.027 N·m
• Shaft: 4 mm
• Type: 2-phase, open-loop

Laboratory and Optical Applications

Optical and laboratory instruments that position sensors, lenses, or small fixtures favor a micro motor with low vibration and negligible heat. The modest current permits simple driver circuitry and small supplies, easing integration into tight instrument designs. Typical duties include adjusting focus, translating specimens, and moving compact fixtures along short rails.

Design Notes

The 4 mm shaft and NEMA8 interface fit compact micro-coupling hardware and small mounting plates. Because torque is small, keep friction low and verify the load at the working speed before committing the axis. For designers who need controlled motion in the smallest practical footprint, this motor delivers a proven, low-power solution. The 20 mm frame is often chosen for OEM instrument modules where the motor is embedded in a larger assembly. Because the output is small, pair it with low-friction guides and light carriages, and use microstepping to smooth motion for the finest positioning steps. Thermal load is minimal, so the motor can be mounted inside sealed housings without extra ventilation.