Custom Frameless BLDC Motor for Robotics

Core Structure of Robot Frameless Brushless DC Motors

A robot frameless brushless DC motor is a customized direct-drive brushless motor designed specifically for robotic joint applications. It represents a high-end segment of brushless DC motors and has become a standard power component in humanoid robots and collaborative robots.

Unlike conventional enclosed brushless motors, this motor eliminates unnecessary mechanical components such as:

• Motor housing

• End covers

• Fixed bearings

• Output shafts

Only two essential electromagnetic components remain:

• Stator winding

• Permanent magnet rotor

This simplified structure is the reason it is called a “frameless motor.”

From an operating principle perspective, it still follows the permanent magnet synchronous drive technology of brushless motors. A motor controller regulates three-phase current to rotate the rotor without brush friction or mechanical commutation losses.

However, it has been specially optimized for robotic applications, featuring the following structural advantages:

Minimal Split Structure for Embedded Robot Integration

The motor consists only of an independent stator and rotor without external mechanical structures.

The stator can be directly mounted inside the robot joint housing, while the rotor can be integrated with the robot’s main shaft.

By utilizing the robot’s own bearings and housing for support and protection, the motor achieves seamless integration with robotic joints, significantly reducing internal space requirements.

Large Hollow Through-Hole Design Solves Robot Wiring Challenges

HOLRY robot frameless brushless motors adopt a large hollow ring structure, allowing:

• Cables

• Pneumatic tubes

• Sensor wiring

to pass directly through the motor center.

This design effectively solves common problems found in traditional motors, including:

• External wiring complexity

• Cable wear

• Joint rotation interference

It greatly improves internal robot layout and supports multi-angle rotation required for humanoid robotic joints.

High-Density Winding Technology for Precision Low-Speed Torque Output

Unlike general high-speed brushless motors, robot-specific frameless motors use:

• High-purity copper concentrated windings

• High-performance NdFeB permanent magnets

The design reduces unnecessary high-speed performance while enhancing:

• Low-speed torque stability

• Precise motion control

• Smooth operation

This makes them ideal for robotic joints requiring slow, accurate, and stable movements, eliminating startup vibration and speed fluctuation.

Robot Frameless Brushless Motor vs Traditional Motors

Based on years of robotic debugging experience and international export applications, traditional brushed motors, enclosed brushless motors, and geared motors all have limitations that prevent them from meeting the requirements of advanced robotics.

Robot frameless brushless DC motors are specifically designed to satisfy four major robotic demands:

• Lightweight design

• High precision

• Fast dynamic response

• Long-term stability

These advantages make them the preferred drive solution for modern robotics.

Zero Transmission Backlash for Maximum Positioning Accuracy

Traditional robot drive systems usually adopt:

Motor + Gear Reducer + Coupling

Multiple transmission stages inevitably introduce:

• Mechanical backlash

• Transmission losses

• Response delay

As a result, robots experience:

• Reduced repeat positioning accuracy

• Delayed movements

• Limited precision performance

Frameless brushless motors use a direct-drive integrated structure, where the rotor and load shaft rotate synchronously without intermediate transmission components.

The result:

• Zero transmission backlash

• Higher control accuracy

• Repeat positioning accuracy up to ±0.05 mm

This fully meets the requirements of:

• Surgical robots

• Precision assembly robots

• Humanoid dexterous hands

Ultra-High Torque Density Enables Lightweight Robots

Robot weight and size are critical factors.

A lighter robot provides:

• Lower energy consumption

• Faster response

• Improved human-machine safety

By removing unnecessary mechanical structures, frameless motors provide:

• 30%-50% higher torque output under the same size and weight conditions

• More than 40% volume reduction under the same torque requirement

They are ideally suited for:

• Humanoid robot limbs

• Collaborative robot joints

• Lightweight robotic systems

Low Inertia and High Response for Smooth Human-Like Motion

HOLRY frameless brushless motors are optimized with precise inertia matching technology.

The extremely low rotor inertia enables:

• Faster response to control signals

• Rapid start-stop operation

• Precise micro-adjustments

This allows humanoid robots to achieve smoother movements in:

• Walking

• Object grasping

• Fine positioning

The brushless structure also provides:

• Silent operation

• No mechanical wear

• Long service life

making it suitable for indoor precision applications.

Designed for Continuous Operation with Higher Reliability

Without mechanical contact wear, these motors provide a service life more than 10 times longer than traditional brushed motors.

They support:

• 24/7 continuous operation

• Maintenance-free performance

• Industrial mass production environments

The stator can directly transfer heat through the robot housing, combined with customized cooling solutions, ensuring:

• Stable temperature control

• No excessive heat rise

• Reduced risk of magnet demagnetization

This significantly improves overall robot reliability.

High Customization Capability for Global Export Markets

For international applications, HOLRY frameless brushless motors support:

• Wide voltage compatibility

• High/low temperature customization

• Improved insulation grades

• Customized dimensions and torque parameters

They can adapt to different:

• Power systems

• Climate conditions

• Robot architectures

in regions including:

• Europe

• North America

• Southeast Asia

• Middle East

Main Application Areas

Based on 10 years of international market experience, more than 80% of frameless brushless DC motor demand comes from robotics applications.

With excellent integration capability and precision performance, they are widely used in advanced robotic equipment worldwide.

Humanoid Robots (Core Application)

Used in:

• Shoulders

• Elbows

• Hips

• Knees

• Wrists

• Dexterous hands

The hollow structure simplifies internal wiring, while high torque density supports:

• Body load capacity

• Flexible movement

• Precise control

making frameless motors the mainstream drive solution for humanoid robots.

Collaborative Robots (Industrial Mainstream Application)

Collaborative robots require:

• Safety

• Lightweight design

• Stability

The advantages of frameless motors, including:

• Low vibration

• Fast response

• Compact structure

help prevent:

• Motion interruption

• Incorrect operation

They are widely used in:

• Automated assembly

• Sorting systems

• Material handling

Medical Precision Robots

Applications include:

• Surgical robots

• Rehabilitation robots

• Medical inspection equipment

Advantages:

• No mechanical wear

• Dust-free operation

• Silent running

• High positioning accuracy

make them suitable for strict medical environments and international certification requirements.

Special and Aerospace Robotics

Applications include:

• Inspection robots

• Exoskeleton robots

• Precision airborne actuators

Customized protection is available for:

• Extreme temperatures

• Vacuum environments

• High humidity

• Dust exposure

supporting global special equipment applications.

How to Select a Robot Frameless Brushless Motor

Many robot developers and overseas buyers only focus on torque and dimensions while ignoring:

• Operating conditions

• Rotor inertia matching

• Cooling requirements

• Electrical compatibility

This often causes integration failures and after-sales problems.

Distinguish Continuous Torque and Peak Torque

Robot joints experience:

• Continuous loads

• Instant impact loads

Selection should consider:

Continuous rated torque for normal operation.

Peak torque for:

• Startup

• Heavy loads

• Short-term overload

Never select motors only based on peak torque.

Insufficient margin may cause:

• Overheating

• Torque reduction

• Motion instability

For heavy-duty applications, at least 20% torque safety margin is recommended.

Match Rotor Inertia for Dynamic Performance

Different joints require different inertia characteristics:

Low inertia motors:

• Dexterous hands

• Wrist joints

Medium/high inertia motors:

• Shoulder joints

• Hip joints

Incorrect inertia matching causes:

• Delayed movement

• Impact during acceleration

• Reduced accuracy

Match Installation Space and Hollow Diameter

Selection should consider:

• Outer diameter

• Motor thickness

• Hollow bore size

The goal is to achieve:

• Maximum torque output

• Compact integration

• Easy assembly

HOLRY supports customized dimensions for various robotic designs.

Match Electrical Parameters with Controllers and Global Power Systems

Frameless brushless motors require dedicated servo drives.

Parameters must match accurately:

• Voltage

• Resistance

• Inductance

Otherwise problems may occur:

• Overcurrent

• Vibration

• Unstable speed control

For export markets, wide-voltage models are preferred to support:

110V-415V global power systems

Customize Protection and Cooling According to Export Conditions

Different regions require different solutions:

Hot and humid areas:

• Enhanced insulation

• Moisture protection

Cold environments:

• Low-temperature magnets

• Cold-resistant windings

24-hour industrial operation:

• Additional cooling systems

Common Selection Mistakes

90% of robot frameless motor issues are caused not by product quality, but by incorrect selection or integration.

Mistake 1: Replacing robot frameless motors with general brushless motors

General motors cannot achieve:

• High precision

• Lightweight design

• Compact integration

required by advanced robots.

Mistake 2: Only Checking Datasheets Without Considering Real Loads

Static laboratory parameters cannot represent dynamic robotic conditions.

Without sufficient torque margin and thermal design, overheating and torque loss may occur.

Mistake 3: Ignoring Rotor-Stator Alignment Accuracy

Improper installation may cause:

• Rotor rubbing

• Vibration

• Excessive noise

which is a common failure factor in overseas assembly environments.

Mistake 4: Using Ordinary Brushless Controllers

Standard controllers cannot fully support:

• Low inertia characteristics

• High dynamic response

of robotic motors.

Mistake 5: Ignoring Overseas Environmental Adaptation

Failure to customize for:

• Voltage standards

• Temperature

• Humidity

may cause:

• Magnet demagnetization

• Moisture damage

• Electrical incompatibility

FAQ

Q1: Does a robot frameless brushless motor require a gearbox?

Most lightweight humanoid and collaborative robots do not require gear reducers. Direct drive technology provides accurate control.

Heavy industrial robots may combine micro precision reducers for higher torque.

Q2: Can a frameless motor operate directly after power connection?

No.

A frameless motor has:

• No bearings

• No housing

• No support structure

It must be integrated with:

• Robot mechanics

• Encoder

• Servo controller

• Cooling system

before operation.

Q3: What adjustments are required for overseas export?

Main considerations include:

• Local voltage compatibility

• Environmental protection

• Temperature adaptation

• English manuals

• Technical documents

• CE certification materials

Q4: What are the lifetime advantages of frameless motors?

Because they have:

• No brush wear

• No mechanical transmission loss

they can operate for tens of thousands of hours under standard conditions, significantly reducing maintenance costs.

Conclusion

The best motor is not the one with the highest specifications, but the one that perfectly matches:

• Robot joint load

• Motion requirements

• Integration space

• Operating environment

Blindly selecting oversized motors or generic replacements only increases development costs and export risks.

With years of experience in robot frameless brushless motor development and manufacturing, HOLRY provides standardized and customized frameless brushless DC motor solutions for global robotics manufacturers.

Our products support:

• Humanoid robots

• Industrial collaborative robots

• Medical precision robots

• Advanced automation equipment

and provide reliable, cost-effective drive solutions for global robotic applications.

For customized motor solutions based on your robot structure, joint load, and target export market, contact HOLRY’s professional engineering team for one-to-one technical support and motor selection guidance.