AC servo motor
B&R Industrial Automation 8LS synchronous motors
Synchronous servo motors with stall torque from 0.8 to 390 Nm (series maximum, force-cooled 8LSP9), nominal speeds from 1,300 to 6,000 rpm and flanges from 58 to 269.9 mm.
Key specifications
| Standstill torque (max) | 390 Nm |
|---|---|
| Rated speed | 1,300–6,000 |
| Frame sizes | 58 x 58 to 269.9 x 269.9 |
| Feedback | wide encoder choice including functional safety encoders |
| Cooling | self-cooled (8LSA, 8LSO) or axial fan (8LSC, 8LSP) |
| Options | holding brake, oil seal, reinforced bearings |
Summarised in our own words from ABB's published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Specify Motion is not affiliated with ABB. B&R Industrial Automation and 8LS synchronous motors are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a B&R Industrial Automation part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These series from our supply network is the closest match on published figures.
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.
View ELM1 / ELM2 AC Servo Motors →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.
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 B&R Industrial Automation 8LS synchronous motors
Send these with your enquiry and an engineer can confirm the right 8LS synchronous motors 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
B&R Industrial Automation 8LS synchronous motors: frequently asked questions
What is the B&R Industrial Automation 8LS synchronous motors?
Synchronous servo motors with stall torque from 0.8 to 390 Nm (series maximum, force-cooled 8LSP9), nominal speeds from 1,300 to 6,000 rpm and flanges from 58 to 269.9 mm. Published series figures include standstill torque 390 Nm. It is made by ABB; Specify Motion can help source it or propose an equivalent.
Who makes the B&R Industrial Automation 8LS synchronous motors?
The B&R Industrial Automation 8LS synchronous motors is made by B&R Industrial Automation (ABB) and is listed here for engineers comparing options. Specify Motion is not affiliated with ABB; brand names are used only to identify the product.
What is the standstill torque of the B&R Industrial Automation 8LS synchronous motors?
The published series maximum standstill torque is 390 Nm. Individual models and sizes in the 8LS synchronous motors 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 B&R Industrial Automation 8LS synchronous motors?
Yes. On published figures, Leadshine ELM1 / ELM2 AC Servo Motors is the closest match 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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