AC servo motor
Siemens SIMOTICS S-1FK2 AC servo motor
Naturally cooled compact servo motor family offered in several inertia classes (CT, HD, HI), built primarily for the SINAMICS S210 one-cable system and also usable on SINAMICS S120/S220.
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What are you specifying?
Select everything you need. A motor, drive and gearbox can be specified together as one axis.
Key specifications
| Ingress protection | IP64 to IP67 (range quoted for the 1FK2/1FT2/1FS2 group) |
|---|---|
| Rated torque | 0.16–40 Nm |
| Rated speed | up to 6000 |
| Power | 50–7,100 W |
| Frame sizes | 20, 100 mm |
| Supply | 1 AC 200-240 V (0.05-0.75 kW, 0.16-3.6 Nm); 3 AC 200-240 V (0.05-3.9 kW, 0.16-40 Nm); 3 AC 380-480 V (0.4-6.4 kW, 1.27-40 Nm) - combined 1FK2/1FT2 figures on S210 page |
| Feedback | single-turn absolute, multi-turn absolute, DRIVE-CLiQ digital interface with electronic nameplate |
| Overload | not published as a figure for 1FK2 alone |
Summarised in our own words from Siemens AG's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1 · Source 2 · Source 3 · Source 4
Notes on this data
Siemens publishes 1FK2 and 1FT2 figures partly combined. S210 page (current) gives 0.16-40 Nm and 0.05-6.4 kW for 1FK2/1FT2 together; 1FK2/1FT2 product page gives 1FK2 rated power 0.26-7.1 kW and a single rated torque figure of 34.5 Nm; 2022 brochure gives 1FK2 standstill torque CT 0.64-40 Nm, HD 0.16-16 Nm. torque_Nm_rated_max of 40 is the combined S210-page figure. Servo planetary gearmotor versions also offered. No peak torque figure published on the pages checked.
Specify Motion is not affiliated with Siemens AG. Siemens and SIMOTICS S-1FK2 are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Siemens SIMOTICS S-1FK2 replacement and alternative options
Use these supply-network options as a starting point for an engineering check. We can also help source the original Siemens part. Published series figures do not establish an exact-model or drop-in replacement: confirm ratings, fit, interfaces and approvals for your application.
Kinco's established AC servo motor range from 40 to 180 mm frames, covering 50 W to 7.5 kW and up to 48 Nm rated torque. Standard feedback is a 2500-line incremental encoder with Hall commutation, with absolute options and a resolver on the 180 mm frame. Pairs with FD2S and CD2S drives.
| Published maximum | SIMOTICS S-1FK2 | SMH Series AC Servo Motors (SMH40S-SMH… |
|---|---|---|
| Rated torque | 40 Nm | 48 Nm meets or exceeds |
| Power | 7,100 W | 7,500 W meets or exceeds |
Kinco's current-generation AC servo motor line, matched to the JD2 and FD5P PRO drives. Small-inertia 40-80 mm frames run at 3000 rpm on 220 V; large-inertia 130 and 180 mm frames are 1500 rpm machines reaching 47.8 Nm rated and 7.5 kW, with 23-bit multi-turn absolute encoders as standard.
| Published maximum | SIMOTICS S-1FK2 | SMK Series AC Servo Motors (SMK40S/60S… |
|---|---|---|
| Rated torque | 40 Nm | 47.8 Nm meets or exceeds |
| Peak torque | — | 119.5 Nm |
| Speed | — | 6,000 rpm |
| Power | 7,100 W | 7,500 W meets or exceeds |
Leadshine's AC servo motors for the EL8/EL7/EL6 drives: ELM1 is the economy line and ELM2 the general-purpose line, both with 23-bit absolute encoders, IP65/IP67 sealing and up to 3.5x overload. The catalogue extends ELM2M to 22 kW and previews a 26-bit ELM3.
| Published maximum | SIMOTICS S-1FK2 | ELM1 / ELM2 AC Servo Motors |
|---|---|---|
| Rated torque | 40 Nm | — |
| Power | 7,100 W | 7,500 W meets or exceeds |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
Typical applications
What an AC servo motor is
An AC servo motor is a permanent-magnet synchronous motor designed for closed-loop control of position, speed and torque. A wound stator is driven by a servo drive with sinusoidal three-phase current, while magnets on the rotor follow the rotating field. A high-resolution encoder or resolver on the shaft feeds position back to the drive, which adjusts current many thousands of times a second. The result is precise, dynamic motion with high peak torque, typically about three times the continuous rating for short periods.
When engineers choose an AC servo motor
Choose an AC servo for machine axes needing fast, accurate motion under varying loads, such as packaging, robotics, machine tools and printing. Compared with steppers, servos keep torque at high speed and cannot silently lose position. The trade-offs are cost and set-up: a servo needs a matched drive, feedback and tuning. For simple, low-speed indexing with a steady load, a stepper may be cheaper. For very low speeds and high torque, a gearbox or direct-drive motor may be needed.
How to specify the Siemens SIMOTICS S-1FK2
Send these with your enquiry and an engineer can confirm the right SIMOTICS S-1FK2 variant or an equivalent:
- Continuous and peak torque (Nm)
- Rated and maximum speed (rpm)
- Load inertia and inertia ratio
- Supply voltage: 230 V single-phase or 400 V three-phase
- Feedback: incremental or absolute encoder, resolution (bits)
- Holding brake, IP code and shaft options
- Flange size and mounting (mm)
Common mistakes to avoid
- Sizing on peak torque without checking RMS torque over the cycle
- Ignoring load-to-motor inertia ratio, which makes tuning hard
- Forgetting the brake is for holding, not dynamic stopping
- Using a motor and drive pair that the supplier has not matched
Siemens SIMOTICS S-1FK2: frequently asked questions
Can you help replace Siemens SIMOTICS S-1FK2 or source the original?
Send the full model code, quantity and required date. Our engineers can check original-part availability and assess suitable alternatives, including supply-network options where appropriate. We confirm compatibility and any changes needed before recommending a replacement.
What is the Siemens SIMOTICS S-1FK2?
Naturally cooled compact servo motor family offered in several inertia classes (CT, HD, HI), built primarily for the SINAMICS S210 one-cable system and also usable on SINAMICS S120/S220. Published series figures include rated torque 0.16 Nm, rated torque 40 Nm, power 50 W, power 7,100 W. It is made by Siemens AG; Specify Motion can help source it or propose an equivalent.
Who makes the Siemens SIMOTICS S-1FK2?
The Siemens SIMOTICS S-1FK2 is made by Siemens (Siemens AG) and is listed here for engineers comparing options. Specify Motion is not affiliated with Siemens AG; brand names are used only to identify the product.
What is the rated torque of the Siemens SIMOTICS S-1FK2?
The published series minimum rated torque is 0.16 Nm. Individual models and sizes in the SIMOTICS S-1FK2 range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Siemens SIMOTICS S-1FK2?
We can assess suitable replacement options. On published figures, Kinco SMH Series AC Servo Motors (SMH40S-SMH180D) and Kinco SMK Series AC Servo Motors (SMK40S/60S/80S, SMK130G, SMK180G) are options to assess from our supply network. An engineer confirms the fit against your application before recommending anything.
What is the inertia ratio in servo sizing?
The inertia ratio compares the load inertia reflected to the motor shaft with the motor's rotor inertia. High ratios make the axis harder to tune and slower to settle. Many engineers aim for below about 10:1, and lower for highly dynamic axes, using a gearbox to reduce reflected inertia where needed.
Do AC servo motors need an absolute encoder?
Not always. Incremental encoders need a homing routine after power-up, which is acceptable on many machines. Absolute encoders know their position at power-on, avoiding homing, which saves time and suits robots and multi-axis machines. Multi-turn absolute encoders track turns even when power is off.
Further reading: How to select a servo motor · Servo vs stepper · Servo and stepper motors
Other ac servo motor series
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From enquiry to delivery
Send a part number or describe the application. Our engineers take it from there: the right product, a clear quotation, and delivery and support arranged.
- 01Tell us what you needSend a part number, or configure the application, quantities and timing.
- 02An engineer reviews itWe check the specification and find the original part, a checked equivalent or a complete axis.
- 03Receive your quotationProducts, pricing, lead time and compatibility notes in one reply.
- 04Order and deliveryWhen you are happy, the order is placed and delivery and after-sales support are arranged.