How does a frameless motor work?

Frameless motors, like all servo motors, work as part of a complete servo system. One or more feedback devices — such as an incremental or absolute encoder, a Hall effect sensor or a resolver — sends information about rotor position to a drive amplifier, which in turn continually fine-tunes rotor position and speed to suit application requirements by means of a series of embedded control loops.

Unlike standard servo motors, frameless motors are supplied as a kit consisting of only a stator with copper windings and a rotor with rare-earth magnets mounted to a hub. This is similar to what you would see if you disassembled a standard motor and discarded the housing, shaft, bearings, feedback device and cable connectors — everything except for the stator and rotor that are directly responsible for producing motion. These are integrated into a housing, bearings and other components of the engineer’s own choice.

This minimalistic form factor of a frameless motor can provide several advantages for certain applications. For example, the housing can be designed as part of the machine structure, providing superior protection from harsh environments. And by eliminating redundant components, frameless motors enable the most compact, lightweight application design — whether direct drive or incorporating the most compact and precise gearing mechanisms.

Talk to an Expert Frameless motor decision guide

Kollmorgen TBM2G Frameless Motor
Kollmorgen KBM Frameless Motor

Frameless motor features

For applications that can’t be optimized using a housed servo motor, frameless motors offer many advantages:

Compact, lightweight form factor. Frameless motors eliminate redundant components, Engineers can directly integrate the housing, bearings, shaft, couplings and other elements into an exceptionally compact application design.

Precise performance. Frameless motors can drive the load directly, with no transmission components required. If gear reduction is needed, they can be directly integrated with compact, low- or zero-backlash planetary, harmonic or cycloidal gearing. Either way, frameless motors respond instantly to changing speed and position demands from the drive while delivering unsurpassed torque density.

Environmental resilience. Embedded directly into the application, frameless motors can be thoroughly protected from caustic washdown fluids, submersion, weather exposure and other environmental hazards. When high temperatures are a concern, the machine structure can provide effective heatsinking, and our TBM2G motors operate efficiently at an exceptionally low thermal rise.

Design freedom. Frameless motors are available in both torque motor (short axial length in relation to diameter) and servo (longer axial length) form factors, and in a wide range of diameters, stack lengths and winding variations. Torque motors take advantage of the D2L rule to deliver maximum torque density. All models eliminate design constraints imposed by the housing, shaft, connector and mounting configuration of a standard servo motor.

Motor selection and sizing. Take advantage of Kollmorgen’s online design tools to achieve the ideal fit and performance characteristics.

Kollmorgen Frameless Motors

What are frameless motors used for?

Learn how frameless brushless DC motors are used in:

Robotics and industrial automation. Frameless motors enable the most compact and powerful robotic joints, enhancing the dexterity, versatility and efficiency of surgical robots, humanoid robots and exoskeletons, industrial cobots and more.

Control Actuator Systems. Frameless motors deliver optimum torque and speed while fitting within an extremely confined installation envelope. And they operate with absolute reliability despite the shocks, vibration and temperatures encountered in flight.

Compact rotary actuators.  Frameless motors support the most compact and powerful actuator designs, enabling the tightest possible motion integration whether driving the load directly or via a compact harmonic, planetary or cycloidal gearset.

Submersible vehicles and robots. To drive compact submersible propulsion systems, frameless motors can be sealed in an oil- or gas-filled pressure vessels for reliable protection against subsea pressures or hazardous liquids.

High-vacuum and high-radiation environments. In applications such as space vehicles, semiconductor processing and radiation-producing medical devices, frameless motors can often be modified with materials that resist outgassing and premature degradation.

Food & beverage production and packaging. In hygienic applications, a frameless motor can be embedded in such a way that washdown fluids can never touch it.

Frameless motors are also ideal for many other industries and applications. Let’s discuss your specific motion requirements and find the best solution.

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Kollmorgen Frameless Motor Application

Frameless motors versus other motor technologies

Frameless versus housed. Frameless motor kits consist of a stator and rotor. They lack the housing, end bells, bearings, rotor shaft, and cable connectors of a housed motor. Instead, these elements are incorporated into the application design.

Frameless versus servo. A frameless motor is a type of servo motor. The choice is whether to use a housed servo motor design or a frameless brushless DC motor.

Frameless (or housed) servo motor versus stepper motor. Rather than relying on feedback loops, stepper motors move through a fixed number of steps per rotation, which can be controlled by discrete pulses from the stepper drive. This can have advantages and disadvantages, depending on the application. Learn more.

Frameless (or housed) servo motor versus induction motor. Induction motors have historically been used for single-speed applications, such as conveyors. Although modern induction motors and drives can incorporate feedback, they are not usually the best choice for highly dynamic applications requiring the most precise positioning.

Frameless motor advantages and disadvantages. Frameless motors are the best choice for applications where using a housed servo motor would impose limitations on the application size and weight, configuration, precision or environmental resilience. They allow engineers to address all these issues in the application design. This can raise application design and prototyping costs, but this is often a worthwhile tradeoff to achieve the most compact, powerful, precise and reliable design.

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Kollmorgen TBM2G Frameless Motor w/ Reflection

Get help with your application

Kollmorgen’s collaborative engineering expertise is unmatched in the motion industry. We have been an innovation leader for more than 100 years, and have decades of experience serving each industry that benefits from stepper or servo technology. Let us help you engineer the exceptional.

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Kollmorgen TBM2G Frameless Motor

TBM2G Series Frameless >

These next-generation frameless motors deliver high torque density for your most compact, lightest electromagnetic package, standard sizing for harmonic gearing, and scalable design to keep you on top of your global production needs.

KBM Series Frameless

KBM Series Frameless >

The KBM series offers high performance, long life, simple installation in a motor kit that can be embedded directly in your mechanical design. A huge selection of standard motors and cost-effective modifications ensure a perfect fit.

TBM Series Medium Image

TBM Series Frameless >

Our TBM series provides direct drive frameless motors designed to be directly embedded in the mechanical structure of your systems, minimizing weight, size and inertia without sacrificing performance.