Frameless motors

Rotor and stator sets designed to be integrated into a joint housing. The surrounding bearings, transmission and cooling are separate design choices.

Inside a frameless motor

Explore the stationary stator and rotating magnet assembly. Bearings, housing and transmission belong to the surrounding joint design.

Drag to rotate · pinch / scroll to zoom

Loading model…

Stator and rotor

The wound stator surrounds a permanent-magnet rotor. Their magnetic interaction produces torque across a small air gap.

About this model

Original Korthos illustrative geometry, not a manufacturer’s product or manufacturing CAD. The windings and magnets are simplified. Dimensions, pole arrangement and winding layout do not specify a validated electromagnetic design.

Model scope & reuse
Architecture, materials & specificationsArchitecture options, material requirements and integration constraints

Architecture options

Slotted versus slotless describes the stator. Inner versus outer rotor is a separate packaging choice.

ApproachMechanismAdvantagesTrade-offs
Slotted statorWindings sit around steel teeth that guide magnetic flux.Can produce high torque within a compact motor.Tooth-to-magnet attraction can create cogging: small torque variations as the rotor turns.
Slotless statorWindings sit in the air gap without stator teeth.Avoids tooth-related cogging for smooth low-speed motion.Torque density and winding heat removal constrain the available joint package.
Inner rotorThe rotor turns inside the stator.Places the stator near the housing, providing a direct heat path.The rotor has a smaller working radius; bearings and wiring still need space.
Outer rotorThe rotor turns around the stator.A larger working radius can increase torque for a given tangential force.Rotating mass, clearance and the heat path from the inner stator constrain integration.

Specifications & operating limits

Continuous torque describes sustained twisting effort under stated cooling conditions. The torque constant relates current to torque. Outer diameter, length and bore describe the space occupied by the motor.

Materials & constraints

Copper windings
More current produces more torque but also more resistive heating. Wire area, winding arrangement and the heat path through the stator constrain sustained output; the surrounding robot housing becomes part of the thermal design.
Laminated electrical steel
Thin insulated steel sheets guide magnetic flux while limiting circulating eddy currents. Lamination thickness, magnetic saturation and the frequency of the changing field influence loss, heating and torque density.
NdFeB permanent magnets
Many permanent-magnet motors use neodymium-iron-boron for strong magnetic fields in a small volume. Grade, temperature resistance, corrosion protection and rotor retention constrain motor performance.
Insulation, resin & adhesives
These electrically isolate and secure the windings and magnets. Their temperature limits and ageing behaviour can constrain the assembly before the metal parts do. Impregnation and thermal contact provide heat paths.

Dependencies & engineering limits

Housing & continuous torque
The stator needs accurate mounting and a heat path into the housing. Nearby gearing, bearings or encoders may reach their temperature limits before the winding does. The lowest thermal limit in the assembled joint constrains sustained torque.
Structure & materials
Assembly & air gap
Bearings and accurately located mounting surfaces keep the rotor centred. Load and temperature changes can alter that air gap through movement or expansion of the surrounding structure.
Bearings
Feedback & usable control
The drive uses rotor-position feedback to control motor current. Encoder mounting error can limit control quality before the motor reaches its mechanical limits.
Encoders & position sensors
Magnet supply
A permanent-magnet rotor uses a specified magnet grade, shape and temperature capability. Changing the magnet can require electromagnetic redesign and thermal testing.

Manufacturing & assembly

Guide

About this route

The route shows one process or architecture. Select a step to see its function and connections; related parts can be parallel inputs or alternatives.

Function

Inputs & dependencies
Outputs & connections
Related processes & parts
Sources

Manufacturing · Representative route. A sintered NdFeB, permanent-magnet motor route.

Related parts & processes 8

NdFeB alloy

Neodymium, iron and boron form the magnetic alloy in this sintered-magnet route. Grade selection trades magnetic performance against temperature requirements.

Heavy-rare-earth additions vary by grade.

Sources & technical scope

Illustrative images of generic materials and components.

Related references
Link to this detail

Production equipment

Market context

Rare-earth magnets

China’s share of global outputChina Rest of world
China · global sintered-magnet output94%
China · global magnet rare-earth refining91%

Global supply across industries. Refining and finished magnets are separate dependencies for permanent-magnet motors.

maxon

4.6mProducts shipped across all markets

Group-wide products, not a count of frameless motors or robot joints. Robotics revenue and unit share are not disclosed.

1 more update

ANYbotics assigned development and production of ANYmal actuators to maxon. Each robot uses twelve drive systems; the agreement moved the actuator programme from small-series development toward industrial production.

Neo

2,000 t/yrFinished magnets · initial nameplate capacity
5,000 t/yrFinished magnets · planned expanded capacity

Narva, Estonia.

Niron

2027Sartell operations · target
Up to 1,500 tons/yrIron-nitride magnets · planned full operation

Iron-nitride magnet manufacturing, with operations targeted for 2027.

MP Materials

≈10,000 t/yrFinished magnets · planned company-wide capacity
202810X commissioning · planned start

Planned company-wide capacity for finished magnets.

eVAC

≈2,000 t/yrFinished magnets · nameplate capacity · Sumter

Sintered NdFeB magnet production in Sumter, South Carolina.

Unitree

Unitree’s integrated joints combine permanent-magnet motors with planetary reducers designed for leg-impact loads. The filing describes this technology as being in mass production.

1 more update

Unitree assembles robots and core modules internally. It buys custom mechanical parts and outsources most PCB assembly, injection moulding and some machining.