NMB SMF25, ST35 and SMW High-Speed PM Stepping Motors Review: Specs, Price and Applications
Updated: 4 days ago
NMB’s high-speed permanent-magnet stepping range includes thin SMF25, ST35 and SMW35–42 motor families with silicon-steel stator construction. These are pulse-driven motor components for external drive electronics. The 48- and 96-step versions differ in full-step angle and electrical characteristics, so diameter and a high-speed label are not enough to select an ordering configuration.
Quick Verdict
Consider these motors for compact paper-feed, printer, scanner or similar OEM mechanisms where a thin PM motor fits the torque-speed duty. Their value is a documented low-profile motor architecture with model-specific performance curves. Compare the load at the intended pulse frequency, and keep pull-in capability, pull-out capability and commanded resolution separate.
NMB SMF25, ST35 and SMW High-Speed PM Stepping Motors at a Glance
Specification | Details |
SMF25-G48 / -G96 | 25 mm outer diameter; 8.5 mm catalog body length; 48 / 96 steps per revolution; 7.5° / 3.75° full steps |
ST35A/B-G96 | 35 mm diameter; 8.7 mm catalog body length; 96 steps per revolution; exact A/B configuration required |
SMW35-G48 / -G96 | 35 mm outer diameter; 13 mm catalog body length; 48 / 96 steps per revolution |
SMW42-G48 / -G96 | 42 mm outer diameter; 16.5 mm catalog body length; 48 / 96 steps per revolution |
SMF25 reference drives | 24 V bipolar chopper; 300 mA per phase; G48 15 Ω and G96 15.2 Ω reference windings |
SMW35 reference drives | 24 V bipolar chopper; G48 500 mA and 8.7 Ω per phase; G96 400 mA and 6.5 Ω per phase |
SMW42 reference drives | 24 V bipolar chopper; 400 mA per phase; G48 8.4 Ω and G96 4.2 Ω reference windings |
Performance documentation | Model-specific pull-in and pull-out torque-versus-pulse-frequency curves; reference conditions apply |
System scope | Motor component; external drive/controller and any required load feedback |
Price | Request a quote for the exact winding, mounting and shaft configuration |
Design and Engineering Assessment
Thin construction can be useful in a compact feed or scan mechanism, but it does not determine the torque available at speed. The catalog curves tie the motor to a particular magnet, winding, excitation and driver. Preserve that configuration when comparing candidates, rather than assigning one torque maximum to every motor with the same outside diameter.
A 96-step motor needs twice the step-pulse rate of a 48-step motor at the same shaft speed under the full-step convention. At 600 rpm, the geometric requirement is 960 versus 480 pulses per second. This comparison is arithmetic, not evidence that either model can move a particular load at that point. Read its matching torque curve and acceleration requirement.
The SMW35 comparison also shows that step count is not the only difference. G48 uses 500 mA and an 8.7 Ω winding in the reference data, while G96 uses 400 mA and 6.5 Ω. Those values must stay with their own model and performance graph. A generic controller setting copied from a neighboring motor may change heating, torque and motion reliability.
Paper-feed and scanning tasks include load variations from rollers, belts, media tension and mechanism friction. A motor that runs freely on a bench may lose synchronism when those disturbances are present. Size for the actual cycle, including acceleration, reversal and warm operation, and define how the machine detects or recovers from a feed fault.
SMF25, ST35 and SMW packaging choices
SMF25 provides a 25 mm motor diameter with an 8.5 mm catalog body length, while the ST35 reference is 35 mm by 8.7 mm. SMW35 and SMW42 use longer 13 and 16.5 mm bodies. The published outline and shaft arrangement must be checked for the exact unit, including PCB, lead routing and mounting features.
A thin body dimension is not the complete installed envelope. Add the shaft projection, pulley or gear, electrical connection and service clearance. Keep radial and axial loading within the selected motor’s requirements and avoid using the small motor bearings as the sole support for an unsuitable overhung mechanism.
Step angle, pulse rate and command scaling
The G48 models use 48 full steps per revolution, or 7.5 degrees per step. G96 uses 96, or 3.75 degrees. If a controller adds microstepping, its pulse interpretation must be specified separately. More command subdivisions can improve smoothness without guaranteeing an equal improvement in mechanical accuracy.
For a feed roller, linear travel also depends on effective roller diameter, gearing and media slip. Calibrate and qualify the actual transport mechanism rather than converting the motor step angle into a guaranteed media-position tolerance.
Pull-in and pull-out curves answer different questions
A pull-in curve concerns starting and stopping synchronously under the stated test conditions. A pull-out curve concerns the running torque boundary once the motor is operating. A motion profile that is feasible with an acceleration ramp may not be feasible as an instantaneous start at the same frequency.
Use the matching winding and magnet curve, then include inertia and friction. The catalog identifies its torque values as reference data and asks designers to consider installation heat radiation and duty. A curve should therefore support a qualified selection, not be presented as a universal continuous-duty certificate.
Driver and thermal integration
The cited SMF and SMW examples use a 24 V bipolar current-regulated chopper drive. Match phase current, winding and switching arrangement; do not treat the bus voltage as permission to connect a low-resistance winding directly to a supply. The drive electronics are external to the motor.
Evaluate motor temperature over the real on/off pattern, including any energized hold. A printer or scanner mechanism may spend substantial time stationary, so holding-current behavior can affect heat even when average mechanical output is low. Confirm the actual ambient and mounting conditions for the supplied configuration.
Application and lifecycle selection
NMB identifies office-automation equipment such as printers and scanners as applications. Select by feed or scan duty, shaft interface, acoustic behavior and life expectations under the real load. Claims of high speed do not establish a noise level or service interval for the assembled mechanism.
Current manufacturer tables use complete references such as SMF25-G48 and SMW35-G96. Some older listings omit the G or use a different SMW42 label. Confirm the manufacturer’s exact replacement reference and drawing before treating an old announcement name as an interchangeable current part.
Commissioning and alternatives
Verify the wiring, full-step or microstep convention and travel scaling at reduced speed. Introduce the intended acceleration ramp and actual mechanism load, then evaluate start reliability, reversals, temperature and repeatability throughout the cycle. Include media jams or other process disturbances in the machine fault-handling design.
Compare against another PM motor, a hybrid stepper or an encoder-equipped motor using the same loaded duty and installation constraints. A closed-loop drive can provide additional error detection or correction, but only when the motor, feedback and controller are specified together. It is a different system scope from a bare PM component.
Applications and Selection
Manufacturer-documented use includes paper-feed and other motion mechanisms in printers, scanners and office-automation equipment. Evaluate the specific load, pulse-rate profile, thermal duty and mechanical interface before selecting a motor for a related OEM mechanism.
For NMB SMF25, ST35 and SMW High-Speed PM Stepping Motors, define the actual machine duty before selecting an ordering configuration. Include the required operating point, available installation space, environment and control interfaces. The specification table describes the product or family; the surrounding machine determines which of those features matters for the intended job.
Price and Value
Price: Request a quote for the exact configuration. Compare the product, compatible control equipment, required mechanical parts, cabling and commissioning as one installed system. A component price alone does not represent the cost of a working automation axis.
Evaluate an alternative against the same duty and acceptance criteria. Match the continuous operating requirement first, then compare transient capability, feedback, mechanical fit and support. This avoids choosing between superficially similar products whose ratings describe different operating conditions.
Pros and Cons
Advantages
Thin motor bodies support compact feed and scan mechanisms
48- and 96-step choices provide explicit step-angle options
Model-specific drive conditions and torque curves support engineering selection
Several diameters and winding choices allow a defined packaging comparison
Limitations
High-speed naming does not establish torque at the intended operating point
Pull-in and running torque limits differ
Drive, load feedback and fault handling are external system responsibilities
Old short names require exact current ordering-code confirmation
Who Should Consider NMB SMF25, ST35 and SMW High-Speed PM Stepping Motors?
Consider the high-speed PM range for an OEM feed or scan mechanism whose required torque-speed cycle fits the exact catalog configuration. Give the driver, acceleration profile, shaft interface and thermal installation the same attention as diameter and step angle.
NMB SMF25, ST35 and SMW High-Speed PM Stepping Motors FAQ
Are these integrated servo motors?
No. The reviewed SMF, ST and SMW products are PM stepping-motor components. They require an external driver and controller, and any needed position feedback must be specified separately.
What changes between G48 and G96?
The full-step count changes from 48 to 96 per revolution, corresponding to 7.5 and 3.75 degrees. Electrical characteristics and torque curves can also differ, so the suffix belongs in the complete specification.
Does 96 steps per revolution guarantee better machine accuracy?
No. It defines the full-step increment. Actual accuracy also depends on the motor, load, transmission, control sequence and any feedback. More command subdivisions are not an accuracy certificate.
What is the difference between pull-in and pull-out torque?
Pull-in concerns synchronous starting or stopping under the documented conditions; pull-out concerns the running limit. Use an appropriate acceleration profile and the matching model curve rather than treating the two as one boundary.
Can the listed 24 V be connected directly to a phase winding?
The reference examples use a bipolar chopper driver with a specified phase current. Select and configure that drive arrangement; bus voltage is not an unrestricted direct-winding supply specification.
Are older SMW42S names interchangeable with current SMW42-G references?
Do not assume interchangeability from the family name. Confirm the full manufacturer code, winding, drawing, shaft and curve for the actual replacement.
Where should they be considered?
NMB identifies printer, scanner and office-automation mechanisms. Evaluate the actual feed or scan load, speed, duty and disturbance conditions before extending that application fit to another OEM mechanism.
What is the price and ordering scope?
Request a quote for the exact motor, winding, magnet, shaft and mounting arrangement. Include the external driver, control, wiring and any feedback or process-fault detection needed for the machine.
Prices are indicative and may change. Confirm the final configuration, commercial terms and delivery schedule before ordering.
