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Miniaturized robotics creates a difficult packaging problem: as robotic hands, compact arms, and articulated mechanisms become smaller, there is less room for the motor, gearbox, encoder, electronics, and mechanical support inside each joint.

Simply reducing motor dimensions does not solve the complete problem. A practical miniature joint needs sufficient torque, an appropriate transmission ratio, position feedback, electrical compatibility, and mechanical reliability while remaining within a tightly restricted installation space.

The Φ20mm Micro Joint Actuator is designed around this type of requirement. The X20 uses a Φ20mm × 20mm form factor and an axial flux motor architecture, with continuous torque of up to 450 mNm, initial torque of up to 800 mNm, and a weight of approximately 37.2–41.6 g.

Why the 20 mm Package Matters

A Φ20mm × 20mm envelope leaves limited space for all the components required in a complete robotic joint.

A conventional motion assembly may need a motor, reduction mechanism, encoder, bearings, housing, winding structure, circuit components, and electrical connections. If these elements are designed as separate modules, the resulting joint can quickly become too large for compact robotic mechanisms.

This becomes more challenging when several axes are positioned close together.

Robotic fingers, miniature arms, and articulated mechanisms often require multiple joints within a relatively small physical area. The dimensions of each actuator can therefore influence the overall size of the finished robot.

The X20 approaches this issue as an integrated joint module, combining motor, reduction, feedback, and mechanical elements within a compact footprint.

Axial Flux Motor Architecture and Torque Density

The motor architecture is an important part of miniature actuator design.

Many conventional motors use a radial magnetic structure. An axial flux motor uses a different arrangement of the active electromagnetic components and can provide opportunities for compact packaging in certain applications.

For a small joint, the benefit should be considered at the complete actuator level rather than by looking at the motor independently. The motor, transmission, housing, and feedback system all need to make efficient use of the available volume.

The X20 is designed to provide more than 30% higher torque density than conventional designs according to the supplied product information.

Torque density is particularly relevant when physical space is limited. Instead of asking only how much torque an actuator produces, designers also need to consider how much output is available for a given volume and weight.

This makes torque density an important parameter for lightweight and highly integrated robotic systems.

450 mNm Continuous Torque in a Miniature Joint

The X20 can provide up to 450 mNm of continuous torque.

Continuous torque is especially relevant when a joint needs to maintain a load or repeatedly perform movements rather than generate only a short-duration output.

For example, a robotic finger may need to hold an object, while a compact articulated mechanism may repeatedly position a component against mechanical resistance. In these situations, continuous torque provides useful information about the actuator's operating capability.

The actuator also offers up to 800 mNm of initial torque. This higher value can be relevant when additional output is required during the initial stage of movement, depending on the load profile and control strategy.

Maximum torque figures should not be treated as universal operating conditions. Actual performance depends on the mechanical load, reduction ratio, voltage, duty cycle, thermal conditions, and control system.

Selecting the Right Reduction Ratio

The motor is only one part of the joint's output system.

The Φ20mm Micro Joint Actuator incorporates a miniature reduction mechanism with available ratios of 15:1, 30:1, and 50:1.

A reduction ratio directly affects the relationship between output torque and speed. A lower ratio can be considered when faster joint movement is important, while a higher ratio provides greater mechanical advantage and can support higher output torque and more controlled movement.

Different joints within the same robot may therefore require different configurations.

For example, a joint responsible for rapid positioning may have different requirements from a finger joint designed to provide controlled movement and holding force.

Having three ratio options gives designers more flexibility when matching the actuator to the mechanical requirements of each axis.

12V, 24V, and 48V Configurations

Electrical compatibility should be considered during the early stages of robot design.

The X20 is available in 12V, 24V, and 48V configurations. The appropriate version depends on the power architecture of the complete robotic system.

For multi-joint equipment, engineers need to consider the power supply, motor driver, wiring, controller, and the number of actuators that may operate simultaneously.

If the existing system is built around a 24V power bus, a compatible actuator configuration can simplify integration. Other systems may be designed around 12V or 48V depending on their electrical requirements.

Confirming voltage requirements before mechanical integration can help prevent later changes to the control and power architecture.

Why Actuator Weight Becomes Important

The X20 weighs approximately 37.2–41.6 g.

The difference may appear minor when considering a single actuator, but total weight can become significant when multiple joint modules are used.

A robotic hand, for example, may require several actuators across its fingers and other mechanisms. Similarly, an articulated robot can contain multiple joints along a moving arm.

Every actuator contributes to the moving mass.

Reducing joint weight can help lower the load imposed on upstream mechanical components and may allow the supporting structure to remain smaller and lighter.

For this reason, engineers evaluating miniature actuators should consider torque-to-weight performance alongside absolute torque.

Absolute Magnetic Encoder for Position Feedback

Miniature joint control also depends on accurate position information.

The X20 integrates an absolute magnetic encoder to provide joint position feedback. The encoder allows the controller to monitor the angular position of the actuator and coordinate motion with other axes.

An absolute encoder provides positional information without relying solely on tracking incremental movement from a previously established reference point.

This can be useful in multi-axis robotic systems where several joints need to work together.

Integrating the encoder into a Φ20mm-class actuator also presents a packaging challenge. The sensing system must occupy minimal space without compromising the mechanical and electrical design of the joint.

SPI Communication for Embedded Control

The actuator uses SPI communication for digital control and data exchange.

For compact robotic systems, the communication interface needs to match the architecture of the controller and the rest of the electronics.

Engineers should determine how each actuator will connect to the control system, how data will be exchanged, and how multiple joint modules will be coordinated.

SPI can be suitable for embedded control architectures where the actuator needs to communicate with a local controller or associated electronics.

Communication compatibility should be checked together with voltage, encoder, mounting, and mechanical requirements rather than being treated as a separate specification.

What a Compact Joint Module Can Enable

The main advantage of a small integrated actuator is not simply that it has a small diameter. Its compact size can make it easier to place several motion axes within a limited mechanical envelope.

Potential applications include:

• Dexterous robotic hands

• Compact robotic arms

• Lightweight articulated mechanisms

• Medical equipment

• Precision instruments

• Intelligent equipment

• Miniature automation systems

• Other highly integrated motion platforms

In a conventional motor-and-gearbox arrangement, separate components may require additional housing space and mechanical connections.

An integrated joint actuator can reduce the packaging complexity by combining several functions into one module.

This can be especially useful when multiple joints need to be installed close together.

Torque Density Versus Overall System Size

For miniature robotics, absolute torque is only one consideration.

A 500 mNm actuator may not be useful if its dimensions prevent it from fitting into the intended joint. Conversely, a very small motor may not provide enough torque to perform the required movement.

The practical objective is to balance:

• Joint dimensions

• Continuous torque

• Initial torque

• Output speed

• Reduction ratio

• Weight

• Voltage

• Feedback

• Communication

• Thermal performance

• Duty cycle

This system-level approach helps engineers avoid selecting an actuator based on a single headline specification.

How Multiple Joints Affect the Design

The impact of actuator dimensions becomes increasingly important as the number of axes increases.

Consider a compact robotic hand containing several independently controlled joints. Each joint requires its own motor, transmission, feedback system, wiring, and mechanical mounting.

If each actuator is only slightly larger than necessary, the cumulative effect can increase the size of the entire mechanism.

A Φ20mm × 20mm actuator envelope can therefore be relevant for applications where joint spacing is highly constrained.

The weight of each module also accumulates across the complete system, making the combination of compact dimensions and relatively low mass useful for lightweight robotic architectures.

VAXOR's Focus on Miniature Motion Systems

Suzhou Vaxor-motor CO.,LTD. was founded in 2024 and develops micro joint actuators and ultra-micro coreless motors for applications including robotics, medical devices, precision instruments, and intelligent equipment.

The company's development approach combines axial flux motor technology, PCB/FPCB winding, electromagnetic optimization, and miniature reduction mechanisms.

Its engineering activities cover motor design, structural development, precision manufacturing, robotics control, and intelligent manufacturing.

For customers developing robotic products, the transition from an experimental prototype to repeatable production can require more than a suitable motor. Mechanical integration, electronics, production consistency, and actuator configuration all need to be considered together.

This is why the actuator should be evaluated as a complete motion module rather than simply as a miniature motor.

What Engineers Should Check Before Selecting a Micro Actuator

Before integrating a small joint actuator, engineers can review several key parameters.

Installation Space

Confirm the available diameter, height, mounting arrangement, and surrounding clearance.

Required Torque

Determine both the continuous torque needed during normal operation and any higher initial or short-duration load requirements.

Joint Speed

Output speed should be considered together with the selected reduction ratio.

Voltage

Confirm whether the system requires a 12V, 24V, or 48V configuration.

Feedback

Determine whether absolute position feedback is required and whether the encoder interface is compatible with the controller.

Communication

Check SPI compatibility and the intended electronic architecture.

Weight

Calculate the total actuator mass when several joints are used together.

Duty Cycle and Thermal Conditions

Continuous operation can create different thermal requirements from intermittent movement. The expected duty cycle should therefore be considered during selection.

Mechanical Integration

Mounting, bearing loads, shaft interfaces, wiring, and surrounding components should all be checked before finalizing the joint structure.

Why Gear Ratio Selection Cannot Be Ignored

The three available ratios—15:1, 30:1, and 50:1—provide different output characteristics.

A 15:1 configuration may be considered when movement speed is relatively important. A 30:1 option can provide a balance between speed and mechanical advantage, while a 50:1 ratio can be considered when greater reduction and controlled output movement are required.

The correct choice depends on the actual joint.

A designer should calculate the required output torque and speed from the robot's load, linkage geometry, acceleration, and operating cycle instead of selecting a ratio based only on the largest available reduction.

Integrating the Actuator Into a Robotic Joint

Mechanical integration should be planned together with electrical integration.

The actuator must fit the joint housing while leaving enough room for wiring and surrounding components. The motor driver needs to support the selected voltage and communication architecture, while the controller must be able to process position feedback from the encoder.

Thermal conditions should also be evaluated. Even a small actuator can generate heat during repeated high-load operation, so the surrounding structure and duty cycle need to be considered.

These factors demonstrate why miniature actuator selection is a system engineering task rather than a simple dimensional comparison.

Balancing Compact Size With Functional Integration

The challenge in miniature robotics is not merely to make every component smaller. The actuator still needs to provide useful torque, controlled motion, feedback, and communication while occupying very little space.

The Φ20mm Micro Joint Actuator combines an axial flux motor architecture with a miniature reduction mechanism and integrated absolute magnetic encoder.

Its Φ20mm × 20mm form factor, continuous torque of up to 450 mNm, initial torque of up to 800 mNm, 15:1/30:1/50:1 reduction options, 12V/24V/48V configurations, and approximately 37.2–41.6 g weight provide several parameters for engineers to match with different compact robotic designs.

Final Considerations

Selecting a miniature actuator should begin with the complete joint requirement rather than the motor diameter alone.

Engineers need to consider available installation space, torque, speed, reduction ratio, voltage, position feedback, communication, weight, duty cycle, thermal conditions, and mechanical integration at the same time.

For compact robotic hands, miniature arms, precision mechanisms, and other multi-axis equipment, integrating the motor, transmission, encoder, and control interface within a small package can simplify the overall joint architecture.

The Φ20mm Micro Joint Actuator is designed for this type of highly integrated motion application, providing a compact platform that combines torque output, reduction, position feedback, and multiple electrical configurations.

For developers looking to fit several controlled motion axes into a restricted space, Suzhou Vaxor-motor CO.,LTD. provides micro motion products aimed at robotics and other compact equipment applications.

Ultimately, the right actuator is determined by the actual load profile and mechanical architecture. When torque, weight, dimensions, feedback, and control requirements all need to fit into the same small joint, an integrated Φ20mm Micro Joint Actuator can be a practical approach to compact robotic motion design.

http://www.vaxor-motor.com
Suzhou Vaxor-motor CO.,LTD.

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