How Hollow Shaft Planetary Actuators Enhance Robotic Joint Performance

Why Traditional Actuators Limit Advanced Robotics

As robots become more compact, capable, and multi-functional, traditional actuator designs are increasingly limiting their performance. Issues like wiring complexity, bulky assemblies, and insufficient torque density create significant integration challenges for modern robotic joints. Understanding these pain points highlights why next-generation actuator solutions are necessary.

• Complex Wiring and Limited Integration

  Traditional actuators often rely on external cables for power, communication, and feedback, which increases system complexity and failure risk. Managing these cables becomes especially difficult in robots with multiple joints, leading to potential interference, wear, and maintenance challenges.

  
  

• Bulky Structure and Difficult Integration

  Conventional actuator setups often consist of separate motors, gearboxes, encoders, and drivers. This distributed architecture increases size and weight, making integration into compact robotic joints more difficult and limiting overall design flexibility.

  
  

• Insufficient Torque Density for Compact Robots

  Many robotic applications—such as humanoid hip joints, quadruped legs, or robotic arms—require high torque in a compact footprint. Conventional actuators frequently fail to provide sufficient torque density without increasing size or weight, forcing trade-offs between strength, speed, and design flexibility.

To overcome these challenges, hollow shaft planetary actuators have emerged as an integrated, high-performance solution, setting the stage for the CubeMars AKH Series in next-generation robotic joint design.

What Is a Hollow Shaft Planetary Actuator

A hollow shaft planetary actuator is a fully integrated robotic actuator module that combines a brushless motor, planetary gearbox, sensors, and drive components into a compact unit with a central hollow shaft. This hollow structure allows cables, signal lines, or mechanical elements to pass directly through the actuator, enabling cleaner layouts and more efficient robotic joint designs. As robotic systems become more compact and complex, this integrated actuator architecture has become increasingly important for improving performance, reliability, and ease of integration.

Core Structural Components

A hollow shaft planetary actuator integrates multiple critical drive components into a single actuator module:

• Hollow shaft channel – allows internal cable routing and structural pass-through

• Brushless motor – provides efficient and precise motion control

• Planetary gearbox – increases torque output while maintaining compact size

• Integrated sensors and feedback systems – enable accurate position and motion control

• Compact housing – supports structural rigidity and simplifies installation

This integrated design reduces the need for external components and simplifies robotic system architecture.

Working Principle of a Hollow Shaft Planetary Actuator

A hollow shaft planetary actuator converts electrical energy into controlled mechanical motion through an integrated motor and planetary gear system. This process enables efficient torque amplification and precise motion output within a compact actuator module.

The working process can be understood in the following stages:

1. Electrical Input
The actuator receives electrical power from the motor controller. This electrical input generates a controlled electromagnetic field inside the brushless motor, initiating rotational motion.

2. Brushless Motor Rotation
The brushless motor converts electrical energy into high-speed rotational motion. Brushless motors provide high efficiency, fast response, and precise controllability, making them ideal for robotic applications.

3. Planetary Gear Reduction
The motor's high-speed rotation is transmitted to the planetary gearbox. The planetary gear system reduces rotational speed while multiplying torque output. This allows the actuator to deliver significantly higher torque without increasing motor size.

4. Torque Amplification and Transmission
Through gear reduction, torque is amplified and transferred efficiently to the actuator output stage. The integrated structure ensures minimal energy loss and high mechanical efficiency.

5. Hollow Shaft Output to the Robotic Joint
The amplified torque is delivered through the hollow shaft output, which directly drives the robotic joint. The hollow shaft also allows cables, sensors, or structural components to pass through the center, enabling compact, clean, and highly integrated robotic joint designs.

By combining efficient torque transmission with a centralized hollow shaft architecture, this actuator design unlocks a range of integration and performance benefits for next-generation robotic systems.

Key Benefits of Hollow Shaft Planetary Actuators

(Why Hollow Shaft Architecture Improves Robotic Integration)

Hollow shaft planetary actuators offer significant advantages over traditional actuator designs by improving integration, efficiency, and reliability. Their unique structural architecture and integrated actuator module design make them particularly well suited for modern robotic systems requiring compact size, high performance, and scalable integration.

Key advantages include:

• Internal Cable Routing
  The hollow shaft allows power cables, signal wires, or mechanical components to pass directly through the actuator. This eliminates external cable routing, reduces clutter, and minimizes the risk of cable interference, wear, or damage during operation.

• Higher Structural Integration
  By integrating the motor, planetary gearbox, and feedback systems into a single compact actuator module, hollow shaft actuators reduce the number of external components. This simplifies mechanical design and improves overall system compactness.

• Simplified Robotic Joint Design
  The centralized, modular actuator architecture makes robotic joints easier to design, assemble, and maintain. Engineers can build cleaner, more efficient robotic systems with fewer mechanical and electrical constraints.

These advantages make hollow shaft planetary actuators an ideal solution for advanced robotic systems and a key innovation driving the evolution of next-generation robotic joint design.

Applications of Hollow Shaft Actuators

Building on these integration and structural advantages, hollow shaft planetary actuators have become an increasingly important solution in modern robotic systems. Their centralized architecture enables more compact joint designs, reduces mechanical complexity, and supports scalable actuator integration. As a result, hollow shaft actuator modules are now widely adopted across a range of advanced robotic applications where performance, compactness, and system reliability are critical.

Humanoid Robots

Humanoid robot joints must deliver high torque within tightly constrained space while maintaining smooth and stable motion. Hollow shaft actuators support compact, centralized joint designs by enabling internal cable routing and reducing external components. This improves structural efficiency, reduces joint bulk, and enhances overall motion performance.

Robotic Arms and Collaborative Robots

For robotic arms and collaborative robots, ease of integration and structural simplicity are key design priorities. Hollow shaft actuators reduce external wiring and minimize the number of separate drive components, enabling cleaner mechanical layouts. This simplifies assembly, improves system reliability, and allows engineers to design more compact and efficient robotic arms.

Exoskeleton and Wearable Robotics

Exoskeleton systems prioritize lightweight, compact actuator solutions that can be seamlessly integrated into wearable structures. Hollow shaft actuator modules allow designers to build centralized joint mechanisms that reduce bulk and improve overall mechanical efficiency. This contributes to improved user comfort, reduced system weight, and more natural assisted movement, all of which are essential for wearable robotic applications.

Industrial and Modular Robotic Systems

Industrial robots increasingly rely on modular actuator architectures to improve scalability and simplify system integration. Hollow shaft planetary actuators enable compact, self-contained joint modules that can be easily integrated into robotic arms and automated machinery. This modular design approach improves system flexibility, reduces maintenance complexity, and supports faster development of scalable robotic platforms.

Introducing CubeMars AKH Series Hollow Shaft Planetary Actuators

To address the integration, efficiency, and reliability challenges in modern robotic systems, CubeMars developed the AKH Series hollow shaft planetary actuators. Designed as compact, integrated actuator modules, the AKH Series combines high torque density, internal cable routing, and a planetary gearbox into a single, space-efficient unit. These features make AKH actuators particularly well suited for advanced robotic joints where performance, compactness, and reliability are critical.

Technical Advantages

• High Torque Density: Strong torque output in a compact size, enabling more powerful joints without increasing footprint.

• Integrated Planetary Gearbox: Improves mechanical efficiency and reduces backlash for higher precision.

• Hollow Shaft Architecture: Allows internal routing of cables and sensors, simplifying joint design.

• Modular Design: Combines motor, transmission, and feedback systems into one unit for easier assembly and maintenance.

• Enhanced Reliability: Fewer external components and protected wiring ensure long-term durability in demanding environments.

AKH Series Model Comparison (Quick Selection Guide)

With hollow shaft architecture, integrated planetary gearboxes, and compact modular design, the CubeMars AKH Series provides a high-performance, scalable, and reliable solution for next-generation robotic joints. The comparison table highlights the key differences between AKH70‑16 and AKH70‑48, allowing engineers to quickly select the right actuator for their application while maintaining integration efficiency and system reliability.

How to Choose the Right Hollow Shaft Actuator

Choosing a hollow shaft actuator doesn't have to be complicated. By breaking the process into clear steps, even newcomers can make informed decisions that balance performance, size, and system integration.

Step 1: Understand Your Joint's Load Requirements

The first step is to determine how much torque your joint needs. This includes both static loads (the weight it must hold) and dynamic loads (forces during movement). Selecting an actuator that can reliably handle these loads ensures the joint operates smoothly and avoids premature wear.

(Tip: Overestimating torque adds unnecessary size and weight, while underestimating torque risks failure.)

Step 2: Consider Space and Weight Constraints

Next, examine how much space you have at the joint and how much weight it can carry. Hollow shaft actuators are inherently compact, but models vary in dimensions and mass.

• For compact robots or wearable devices, prioritize smaller, lighter actuators.

• For heavy-duty robotic arms or large joints, higher torque actuators may be slightly larger but necessary for reliable performance.

(Reasoning: The right balance of size and torque keeps the robot agile and efficient without compromising strength.)

Step 3: Check Integration Features

Hollow shaft actuators often come with built-in features like internal cable routing, planetary gearboxes, and integrated feedback electronics. Evaluate which features your design requires:

• Internal routing reduces wiring clutter and protects cables from wear.

• Integrated gearboxes improve mechanical efficiency and reduce backlash.

• Built-in feedback simplifies control and reduces external components.

(Tip: Matching actuator features with your system architecture prevents unexpected redesigns later.)

Step 4: Align with Your Application

Finally, consider your application type and priorities:

• Humanoid or wearable robots → prioritize compactness, lightweight, and smooth joint movement.

• Industrial or load-intensive robots → prioritize torque output, durability, and precision.

(Reasoning: Understanding the application ensures you select an actuator that not only meets specifications but also fits real-world usage.)

Summary

By following these steps—assessing load, evaluating space and weight, checking integration features, and aligning with application needs—engineers can systematically select the right hollow shaft actuator. This approach ensures joints are efficient, reliable, and well-suited for their intended robotic platform, without guesswork or trial-and-error.

Conclusion 

Hollow shaft planetary actuators represent a key innovation in modern robotics, offering compact integration, high torque density, and simplified joint design. From internal cable routing to modular actuator architecture, these features help engineers build more reliable, efficient, and scalable robotic systems.

By understanding actuator benefits, evaluating application needs, and following a structured selection process, engineers—whether newcomers or experienced designers—can confidently choose the right actuator for their next-generation robotic projects.

Take Action

Ready to bring your robotic designs to the next level? Explore the CubeMars AKH Series and discover hollow shaft actuators that combine power, precision, and compact integration.

• Learn more about AKH models: AKH70‑16 V1.0 KV41  | AKH70‑48 V1.0 KV41

• Request a quote or consultation to find the perfect actuator for your robotic joint.

• Download technical resources to see detailed specs, integration tips, and performance benchmarks.

Whether your project focuses on compact wearable robots or high-load industrial arms, choosing the right hollow shaft actuator is the first step toward efficient, reliable, and high-performance robotic design.