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Allen-Bradley MPL-B420P-RK72AA Servo Motor — Detailed Product Introduction, Specifications, Applications, Advantages and Related Models

The MPL-B420P-RK72AA is a low-inertia rotary servo motor designed for industrial motion-control systems. It belongs to the MP-Series MPL family and uses a resolver for feedback, a keyless shaft, a right-angle SpeedTEC DIN connector, and no integral brake.

This model is particularly suitable for machinery that requires high-speed rotation, accurate closed-loop positioning, rapid acceleration and deceleration, and reliable servo feedback.

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1. Basic Product Information

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2. Product Overview

The MPL-B420P-RK72AA is a 5000 RPM low-inertia servo motor intended for demanding industrial motion-control applications.

It combines a 115 mm frame, 50.8 mm magnet stack, approximately 4.74 N·m continuous torque, and approximately 13.5 N·m peak torque in a relatively compact motor package.

The motor uses resolver feedback, which provides rotor position information to the servo controller. This makes the motor suitable for closed-loop applications where controlled speed, position accuracy, repeatability and dynamic response are required.

One of the most important differences between this model and the closely related MPL-B420P-RJ72AA is the shaft arrangement. The RK72AA version uses a keyless shaft, while the RJ72AA version uses a keyed shaft.

Another important feature is that the RK72AA does not include an integral brake. This makes it a good choice when a holding brake is not required or when the machine uses a separate mechanical holding solution.

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3. Brand and Product Series

The MPL family is designed around the requirements of industrial servo motion.

Within this family, different suffix combinations can change the feedback technology, shaft configuration and brake arrangement. Therefore, two MPL motors with very similar electrical ratings may not be direct mechanical or electrical replacements for each other.

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4. Detailed Technical Specifications

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5. Dimensions and Weight

Physical dimensions are particularly important when this motor is being used as a replacement.

For the MPL-B420P-RK72AA, the motor belongs to the 115 mm frame class and has a 50.8 mm magnet stack length.

For practical equipment planning, an overall envelope of approximately 133 × 187 × 98 mm can be used as a preliminary dimensional reference.

The actual installation envelope can be affected by the connector, cable bend radius, mounting hardware, shaft coupling and cable routing.

For this reason, the approximate dimensions above are more appropriate for preliminary equipment planning than for final mechanical drawing approval.

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6. Motor Performance

The MPL-B420P-RK72AA provides approximately 4.74 N·m of continuous torque and approximately 13.5 N·m of peak torque.

The difference between continuous and peak torque is important in servo applications.

Continuous torque describes the torque the motor can provide during normal continuous operation under the applicable operating conditions.

Peak torque is useful when the machine needs additional torque for a short period, such as during:

• Rapid acceleration
• Rapid deceleration
• Positioning
• Indexing
• Overcoming short-duration load changes
• High-dynamic machine cycles

This makes the motor especially useful for equipment that does not simply rotate continuously at a fixed speed, but instead repeatedly starts, stops, accelerates and changes position.

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7. 5000 RPM High-Speed Capability

The 5000 RPM speed rating is one of the key characteristics of the MPL-B420P-RK72AA.

High rotational speed allows the motor to be used in applications where cycle time and rapid rotary movement are important.

Typical examples include:

• High-speed indexing
• Packaging machinery
• Feed mechanisms
• Rotary transfer equipment
• Conveyor synchronization
• Automated assembly
• Material-handling equipment
• High-speed positioning mechanisms

A 5000 RPM servo motor can also be useful when a gearbox or mechanical transmission is used to convert high motor speed into a lower output speed with increased output torque.

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8. Low-Inertia Design

The MPL-B420P-RK72AA is part of a low-inertia servo motor family.

Low rotor inertia is particularly useful when the machine needs fast changes in rotational speed.

For example, imagine a positioning mechanism that moves from one location to another, stops, waits briefly and then moves again.

The motor must repeatedly:

1. Accelerate.
2. Reach the required speed.
3. Decelerate.
4. Stop accurately.
5. Reverse or accelerate again.

A low-inertia motor is well suited to this type of operating cycle.

This characteristic can contribute to shorter machine cycle times, better dynamic response and easier servo optimization when the mechanical load is appropriately matched to the motor.

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9. Resolver Feedback

The MPL-B420P-RK72AA uses a resolver as its feedback device.

The resolver provides rotor position information to the servo control system.

Resolver feedback is commonly used in industrial servo applications where a robust feedback method is required.

Potential advantages include:

• Robust construction
• Good resistance to industrial environments
• Reliable rotor position feedback
• Suitability for repetitive motion
• Compatibility with resolver-capable servo control systems

The feedback type is an important part of the model number.

Therefore, the motor should not be replaced simply by choosing another 115 mm motor with the same torque and speed.

The replacement motor must also be compatible with the feedback requirements of the servo drive.

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10. Keyless Shaft

The RK72AA configuration uses a keyless shaft extension.

This is an important mechanical difference compared with keyed-shaft versions in the same family.

A keyless shaft can be advantageous when the machine uses an appropriate clamping coupling or other shaft connection that does not require a traditional key.

Potential benefits include:

• Flexible coupling arrangements
• Reduced dependence on a shaft key
• Convenient clamping-type mechanical connections
• Good suitability for precision coupling systems
• Clean shaft geometry

However, the machine’s existing coupling must be compatible with the keyless shaft.

A keyed coupling should not simply be assumed to fit a keyless configuration.

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11. No Integral Brake

The MPL-B420P-RK72AA is a no-brake configuration.

This is one of the clearest differences between the RK72AA and RK74AA models.

The no-brake design can be preferable for horizontal rotary applications where a holding brake is not necessary.

It can also reduce unnecessary components when the machine already has another suitable holding mechanism.

For a vertical axis, however, the absence of a brake should be carefully considered because the motor may not be able to hold a gravity-loaded load in place when servo power is removed.

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12. Right-Angle SpeedTEC DIN Connector

The motor uses a right-angle SpeedTEC DIN connector.

The right-angle connector arrangement can be useful in compact machinery because it can reduce the amount of space required directly behind the motor.

The connector can also be rotated through its designed range, which provides additional flexibility when routing motor cables.

This is especially useful when the motor is mounted close to:

• Machine frames
• Safety covers
• Gearboxes
• Linear slides
• Other motors
• Cable trays
• Mechanical guards

Good connector orientation can significantly simplify machine wiring.

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13. Product Applications

13.1 Packaging Machinery

The motor is well suited to packaging equipment that requires repeated high-speed positioning.

Typical applications include:

• Product feeding
• Film feeding
• Rotary indexing
• Cutting mechanisms
• Labeling mechanisms
• Sealing mechanisms
• Conveyor synchronization
• Packaging-axis positioning

The servo system can coordinate motor position with product position and machine timing.

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13.2 Automated Assembly Equipment

Assembly machinery frequently requires precise and repeatable movement.

The motor can be used for:

• Component positioning
• Transfer mechanisms
• Rotary indexing
• Tool positioning
• Automated insertion
• Mechanical feeding
• Workpiece positioning

The low-inertia design is particularly useful when the machine performs many short movements during each production cycle.

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13.3 Material Handling

The motor can be used in automated material-handling systems where controlled movement is required.

Typical examples include:

• Transfer mechanisms
• Conveyor positioning
• Rotary handling
• Sorting mechanisms
• Feed systems
• Automated transport mechanisms

The no-brake configuration is particularly suitable for applications where the driven mechanism does not require an integrated holding brake.

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13.4 Indexing Systems

Indexing is one of the natural applications for a high-speed servo motor.

A typical indexing sequence might be:

Accelerate → Move → Decelerate → Stop → Hold Position → Repeat

The combination of high speed, low inertia and closed-loop resolver feedback makes this type of operation well suited to the motor.

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13.5 Machine Tools

The motor can be used in suitable machine-tool auxiliary or positioning applications.

Possible uses include:

• Feed mechanisms
• Rotary positioning
• Tool positioning
• Auxiliary axes
• Indexing mechanisms
• Material positioning

The exact suitability depends on load inertia, required accuracy, duty cycle and drive compatibility.

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13.6 Pick-and-Place Systems

Automated pick-and-place systems often require rapid changes in speed.

The low-inertia construction can help the motor respond quickly to repeated acceleration and deceleration commands.

Potential applications include:

• Rotary pick-and-place mechanisms
• Transfer axes
• Part orientation
• Product positioning
• Automated sorting

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14. Main Product Advantages

14.1 High-Speed Performance

The 5000 RPM capability provides a strong advantage for machines that require fast rotary movement.

This can help shorten mechanical movement times and improve overall machine productivity.

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14.2 Low-Inertia Response

The low-inertia construction allows the motor to respond quickly to changes in commanded speed.

This is particularly valuable in machines with short and repetitive operating cycles.

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14.3 Good Torque Density

Approximately 4.74 N·m continuous torque and approximately 13.5 N·m peak torque provide a useful combination of continuous and transient performance.

This allows the motor to handle both normal operating loads and short-duration acceleration demands.

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14.4 Resolver Feedback

Resolver feedback provides a robust position-feedback solution for industrial servo control.

This makes the motor suitable for demanding industrial environments where reliable feedback is important.

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14.5 Keyless Shaft

The keyless shaft configuration gives machine builders an alternative to traditional keyed mechanical connections.

It can work particularly well with compatible clamping-type couplings and precision mechanical transmission components.

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14.6 Compact 115 mm Frame

The 115 mm frame provides a useful balance between output capability and physical size.

The motor can provide significant servo performance without requiring a very large motor housing.

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14.7 Right-Angle Connector

The right-angle connector helps with cable routing in compact machinery.

It can reduce interference between the motor cable and surrounding machine structures.

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14.8 No Unnecessary Brake

For applications that do not require a holding brake, the no-brake configuration avoids adding a brake that the machine does not need.

This can simplify system design and reduce unnecessary wiring.

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15. Recommended Five Related Models in the Same Series

The following models are closely related to the MPL-B420P-RK72AA and are useful when selecting an alternative configuration.

Related Model Analysis

The MPL-B420P-RJ72AA is probably the most straightforward alternative when the application needs resolver feedback and no brake, but the machine requires a keyed shaft rather than the keyless shaft of the RK72AA.

The MPL-B420P-RJ74AA maintains the resolver and keyed shaft arrangement but adds a 24 V DC brake.

The MPL-B420P-RK74AA is mechanically very close to the RK72AA because it retains the keyless shaft and resolver feedback while adding the brake.

The MPL-B420P-MK72AA changes the feedback technology to multi-turn high-resolution feedback while retaining the keyless shaft and no-brake configuration.

The MPL-B420P-MK74AA combines the keyless shaft with multi-turn high-resolution feedback and a 24 V DC brake.

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16. Five Popular Models from the Same Brand

The following five models are useful products for comparison when selecting servo motors for industrial automation.

These five models represent useful alternatives across different motor sizes and performance levels.

The B320P and B330P are suitable when a smaller motor is sufficient.

The B420P is a good middle-range choice when the application needs approximately 4.74 N·m continuous torque and 5000 RPM.

The B430P provides additional torque when the B420P is not sufficient.

The B4530F is more appropriate when the application requires a larger motor and substantially greater torque capacity.

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17. B420P Family Comparison

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18. RK72AA vs. RK74AA

The two models are very similar, but one difference is especially important.

If the machine does not require a holding brake, the RK72AA is the simpler choice.

If the machine needs the motor to hold a load after servo power is removed, the RK74AA is more appropriate, provided the brake capacity and machine safety design are suitable.

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19. RK72AA vs. RJ72AA

The RK72AA and RJ72AA have very similar electrical performance.

The primary mechanical difference is the shaft.

If the existing machine uses a keyless coupling, the RK72AA is the more natural choice.

If the machine uses a traditional keyed coupling, the RJ72AA is normally the more convenient configuration.

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20. Advantages for Machine Builders

From a machine-building perspective, the MPL-B420P-RK72AA offers a useful combination of performance and mechanical flexibility.

Its 115 mm frame gives the machine a relatively compact motor package while still providing approximately 4.74 N·m continuous torque.

The 5000 RPM speed capability is useful for high-cycle machinery.

The low-inertia rotor is well suited to rapid acceleration and deceleration.

The resolver feedback provides closed-loop rotor position information.

The keyless shaft allows the use of suitable clamping-type couplings.

The right-angle connector helps simplify cable routing where rear clearance is limited.

The absence of an integral brake makes the motor appropriate for applications where a brake is unnecessary or where a separate mechanical holding system is already installed.

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21. Typical Selection Situations

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22. Installation Considerations

Before installing the MPL-B420P-RK72AA, several points should be checked.

Mechanical Compatibility

The motor mounting dimensions, shaft arrangement, coupling, flange and available installation space should all be checked.

Because this is a keyless shaft model, the machine coupling must be compatible with the shaft configuration.

Electrical Compatibility

The servo drive should support the motor’s electrical characteristics and resolver feedback.

The motor and drive should be treated as one complete servo system rather than as independent components.

Cable Routing

The right-angle connector provides useful flexibility, but adequate cable bending space should still be maintained.

The motor cable should not be forced into a sharp bend immediately at the connector.

Load Matching

Motor sizing should consider:

• Continuous load torque
• Peak load torque
• Acceleration requirements
• Deceleration requirements
• Load inertia
• Operating speed
• Duty cycle
• Gear ratio
• Mechanical efficiency

A motor that is suitable based only on continuous torque may still be unsuitable if the machine has very high acceleration requirements.

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23. Advantages and Limitations

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24. Overall Product Evaluation

The MPL-B420P-RK72AA is a strong choice when the machine requires a high-speed, low-inertia servo motor with resolver feedback and a keyless shaft, while an integral holding brake is not required.

Its combination of 5000 RPM speed, approximately 4.74 N·m continuous torque, approximately 13.5 N·m peak torque and 115 mm frame size makes it suitable for a wide range of industrial motion-control applications.

The keyless shaft is particularly relevant when the machine uses a clamping coupling or another shaft connection designed for a shaft without a key.

The no-brake configuration is best suited to applications where the axis does not require integrated motor holding after power removal.

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25. Final Product Summary

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Conclusion

The MPL-B420P-RK72AA is a 5000 RPM, 115 mm-frame, low-inertia servo motor in the MP-Series MPL family.

Its main specifications are approximately 4.74 N·m continuous torque, 13.5 N·m peak torque, 1.9 kW continuous power, 50.8 mm magnet stack length, resolver feedback, keyless shaft, right-angle SpeedTEC DIN connector, and no integral brake.

Its approximate physical envelope is 133 × 187 × 98 mm, with an approximate weight of 5.70 kg.

The model is particularly attractive for machinery requiring fast acceleration and deceleration, repeated positioning, high-speed rotary movement and reliable closed-loop servo control.

Compared with the closely related models, the most important selection points are the keyless shaft and no-brake configuration. If a keyed shaft is needed, the RJ72AA configuration is the more relevant alternative. If a brake is required, the RK74AA configuration is the closer choice. If a different high-resolution feedback system is preferred, the MK72AA and MK74AA configurations become relevant alternatives.

For industrial automation applications where speed, dynamic response, compact construction and accurate motion control are more important than having an integral holding brake, the MPL-B420P-RK72AA is a practical and versatile servo motor configuration.