What is a Hollow Motor
1.What Is a Hollow Motor?
A hollow motor is a motor with a through-hole in the center of the shaft.
2.Advantages of Hollow Motors
Cables, air tubes, optical components, lasers, and other parts can be routed through the hollow bore. This helps save space, simplify machine design, and improve overall equipment performance and positioning accuracy.
Why Use a Hollow AC Servo Motor?
By mounting the motor directly on the shaft and routing components through the center, you can reduce misalignment caused by couplings and minimize mechanical errors. This supports more stable motion control, more accurate feedback, and higher system precision.
Hollow Shaft Options
Standard features
■ Hollow shaft ratio of 30% relative to the outer diameter. Hollow-shaft optimization options are also available.
■ Tapped hollow shaft: Custom tapping sizes are available. This allows direct connection of a rotary joint, enabling cable or air-tube pass-through without contact with the hollow-shaft end face.
■ Enlarged inner diameter: The hollow bore can be expanded to match your required size.
■ Custom shaft shape design is also available.
Quiet operation
No gear meshing noise, helping reduce total machine operating noise.
Higher accuracy
No backlash-related mechanical error,
supporting high-precision positioning.
Space saving, smaller and lighter
Better acceleration
Backdrivability
A key advantage for haptic feedback in master-slave control systems.
*We introduce this concept using the da Vinci surgical robot as an example.*
Application Examples and Custom Options Unique to μDD Motors
Simple SCARA, Direct Teaching
Robots designed to work alongside people require built-in safety and intuitive operation. With μDD Motors, you can develop collaborative robots that are easy to use and easy to control. By routing cables through the hollow shaft, the overall system can also be made more compact. This is an internal MTL demo unit.
Tapping Inside the μDD Motor Hollow Shaft
We added an M5 × 0.8 thread inside the hollow shaft of an MDH-30 series motor.
This thread enables direct connection of a rotary joint.
It is a strong fit for small-part end effectors and for index tables that require vacuum pickup and holding together with rotary drive.
Product Lineup
From the world’s smallest hollow-shaft direct drive motor to low-speed, high-torque models, we offer a wide product lineup. These motors help simplify mechanical design, reduce parts, and improve positioning accuracy.
MDS/MDH-20 Series
World’s smallest class through-shaft servo motor.
Ideal for end effectors such as hands, grippers, and Zθ units.
Also suitable for compact hand mechanisms when combined with a low reduction-ratio gear.
■ Body diameter: φ21 mm
■ Body length: 31.5 / 37.5 / 43.5 mm
■ Max torque: 40 / 90 / 130 mN·m
■ Max speed: 3,000 rpm
■ Max resolution: 288,000 P/R (after x4), 18-bit
■ Hollow bore: φ2.6 mm (MDH type)
MDS/MDH-30 Series
Ideal for high-precision dispensers and compact gimbal drives.
You can add threads inside the hollow shaft and mount a rotary joint to pass an air tube through the center.
■ Body diameter: φ30 mm, body length: 32 / 38 / 44 mm
■ Max torque: 140 / 280 / 420 mN·m
■ Max speed: 1,000 rpm
■ Max resolution: 432,000 P/R (after x4), 19-bit
■ Hollow bore: φ4 mm (MDH type)
MDH(12)-40 Series
An enlarged inner-diameter version of the MDH-40 series.
It allows cables, lasers, and other components to pass through a φ12 mm bore.
■ Body diameter: φ40 mm
■ Body length: 31.5 / 37.5 / 43.5 mm
■ Max torque: 0.33 / 0.70 / 1.0 N·m
■ Max speed: 450 rpm
■ Max resolution: 1,296,000 P/R (after x4)
■ Hollow bore: φ12 mm
MDH-60 Series
Compact motor with a large-diameter hollow shaft.
Ideal for end effectors and robot joints.
■ Body diameter: φ60 mm
■ Body length: 31.5 / 37.5 / 43.5 mm
■ Max torque: 1.1 / 2.1 / 2.7 N·m
■ Max speed: 300 rpm
■ Max resolution: 2,000,000 P/R (after x4), 20-bit
■ Hollow bore: φ20 mm
MDH70 Series
Compact motor with a large-diameter hollow shaft, ideal for index tables.
A strong alternative to rotary actuators, and also suitable for robot joints such as elbow and shoulder axes.
■ Body diameter: φ70 mm
■ Body length: 31.5 / 37.5 / 43.5 mm
■ Max torque: 1.0 / 2.2 / 3.1 N·m
■ Max speed: 200 rpm
■ Max resolution: 2,592,000 P/R (after x4)
■ Hollow bore: φ25 mm
MDH-100 Series
High-performance design: High torque and high accuracy in a compact body
Ideal for robotics: High backdrivability and support for battery-powered systems
Customization and integration: A wide range of options to match your application requirements
-Applications-
• Base joint axes of robot arms (high rigidity, high torque, hollow shaft)
• AGV wheels (high rigidity, high torque, battery operation)
• Semiconductor equipment (high torque, hollow shaft, high resolution)
■ Body diameter: φ100 mm
■ Body length: 43.5 mm
■ Max torque: 9.6 N·m
■ Max speed: 200 rpm
■ Max resolution: 21-bit
■ Hollow bore: φ40 mm
