B&R 8MSA4S.R0-31 Servo Motor

Product Introduction & Engineering Value

The B&R 8MSA4S.R0-31 is a compact synchronous servo motor intended for integration with B&R motion-control hardware. Its R0 resolver feedback is an important part of the model identification; the motor is not simply interchangeable with another 8MS motor that has a different feedback arrangement. Available documentation also identifies two circular connectors for power and feedback.

For legacy machinery, the value of this motor is straightforward: it can preserve an existing axis architecture without forcing a complete servo-system redesign. The practical question is not whether another motor physically fits. It is whether the replacement matches the drive, feedback, electrical ratings, mounting geometry, and machine parameters.

Technical Specifications

The IP65, Class F insulation, six-pole construction and natural-cooling characteristics are reported by industrial automation suppliers.

There is an important documentation caveat: secondary-market databases do not agree on every dimensional and electrical parameter. For example, one source gives approximately 4.5 kg while another mechanical-data section reports approximately 3.2 kg.

For procurement, treat the actual motor nameplate and original B&R machine documentation as the controlling specification.

8MSA4S.R0-31

8MSA4S.R0-31

Field Application & the “Trench” Experience

Consider an older packaging machine where one servo axis begins producing resolver-related faults. The motor has accumulated years of operating hours, while the rest of the motion system remains serviceable. The maintenance team finds an 8MSA4S.R0-31 as a replacement and assumes the job is simply mechanical.

It isn’t.

The first check should be the resolver interface and motor identification. The ACOPOS-side configuration must correspond to the replacement motor. Then verify the power connector, feedback connector, shaft, mounting dimensions and machine parameters before enabling the axis. The available documentation specifically states that this motor is intended for use with the B&R ACOPOS servo-drive family, rather than direct connection to mains power.

Niche applications

• Packaging-machine indexing and feed axes where resolver feedback is already integrated into the motion architecture.
• Plastic-processing auxiliary axes requiring replacement of a legacy B&R synchronous motor without changing the complete drive system.
• Metal-processing machine positioning axes where an existing ACOPOS installation has to remain in service.

Transparency SOP: QA & Testing

For New Surplus inventory, a credible inspection process should include:

1. Identity check — verify the complete 8MSA4S.R0-31 part number on the physical nameplate.
2. Visual inspection — examine the housing, flange, shaft, connectors and seals for impact, corrosion or storage damage.
3. Winding inspection — perform appropriate winding-resistance and insulation checks before energization.
4. Resolver verification — inspect resolver wiring and confirm feedback integrity.
5. Mechanical check — rotate the shaft manually and check for bearing roughness, abnormal play or binding.
6. Controlled run test — where equipment is available, operate the motor with an appropriate B&R-compatible servo drive and verify feedback and basic motion behavior.

For refurbished units, request the supplier’s actual test report rather than accepting “tested” as sufficient evidence.

Also separate supplier warranty from OEM warranty. One independent supplier advertises a one-year warranty on its own supplied units, while another repair supplier advertises a 12-month whole-unit warranty. Those are supplier warranties, not automatically B&R factory warranties.

The Veteran’s Tech Trap Guide

⚠️ Trap #1 — Confusing 8MSA4S.R0-31 with another 8MSA4 variant

The suffix is significant. R0-31 identifies a particular motor configuration. A nearby 8MS model may have different speed, torque, feedback, or mechanical characteristics. Match the complete part number.

⚠️ Trap #2 — Assuming the resolver is optional

It isn’t something you should ignore during replacement. The 8MSA4S.R0-31 is documented with resolver feedback. If the drive configuration expects a different feedback technology, the replacement is not a plug-and-play substitution.

PRO TIP: Photograph the original motor’s nameplate and both connectors before disconnecting it. Record the ACOPOS axis configuration at the same time.

⚠️ Trap #3 — Trusting a reseller’s specification table blindly

This model has inconsistent secondary-market data. One source lists 2.3 Nm at 3,000 RPM and 330 V, while other pages provide different or incomplete figures.

For a critical spare, ask the seller to photograph the actual unit, including the complete nameplate. Do not purchase solely from a catalog image.

Dynamic FAQ

Is the 8MSA4S.R0-31 a servo motor or a conventional AC motor?

It is a three-phase synchronous servo motor in B&R’s 8MS family. It is intended to operate as part of a closed-loop motion-control system.

What is the rated speed?

Published product information identifies 3,000 RPM as the rated speed.

What feedback does this model use?

The R0 configuration is associated with an integrated resolver feedback system. Confirm the connector and resolver configuration against the existing machine before replacement.

Can I connect the motor directly to 330 VAC?

No. The available technical documentation states that the motor should be operated through a compatible B&R ACOPOS servo drive, not connected directly to the mains.

Is the 8MSA4S.R0-31 still available as new stock?

It remains available through secondary-market automation suppliers. Current listings include new, refurbished, repair and used-stock channels, but condition varies significantly by supplier.

How should I verify New Surplus authenticity?

Ask for photographs of the actual motor and nameplate, not just a stock photograph. Confirm the exact 8MSA4S.R0-31 marking, physical condition, warranty terms, and whether the warranty is supplier-backed or OEM-backed. One supplier explicitly states that it is an independent B&R parts supplier and that its one-year warranty is its own coverage.