Frameless Brushless Motor

Brushless motors have no brushes that physically move on a commutator, and instead use electronics to switch current between the coils of the stator. This results in lower maintenance, low EMI and higher power density.

Frameless motors are designed to mount directly to the machine assembly, replacing coupling devices such as gearboxes and belts. This direct drive connection allows for increased machine performance and efficiency by eliminating backlash and compliance.

Large Diameter

Frameless motors, also known as direct drive motors, allow you to directly mount your rotor to the load for more space and efficiency. Designed to be built in as an integral part of your application, frameless torque motors can eliminate additional mechanics like worm wheels, belts or pulleys.

These high-performance, compact motors offer the highest torque density available, allowing you to pack more power into a smaller package with lower inertia for quicker acceleration and higher servo loop bandwidth. This makes them a great choice for machine tools, centrifuges, robots, winders and other high-speed applications.

The frameless design of a motor eliminates the shaft, bearings and end-caps to reduce weight with more mechanical freedom. Allied Motion’s HT and Megaflux frameless motors include standard models up to 792 mm in diameter, which means they can handle massive loads and high speed.

By using a custom winding option, you can tailor your motor to meet your exact specifications. In addition, our online frameless motor performance curve tool allows you to see how your motor and system will perform based on different bus voltages, amplifier current ratings and ambient temperature limitations. This allows you to select the right size and performance motor for your application without having to guess ahead of time. This can save you time and money on the development process.


A typical electric motor is a self-contained unit about the size of a lemon that you can hold in your hand. It consists of a rotor and stator. These are usually bolted into larger machines in order to add rotational motion to the system. However, for some applications, it is advantageous to have the motor embedded directly into a machine’s structure.

Frameless servo motors allow for this integration by eliminating the end caps. As a result, they Frameless brushless motor can fit into tight spaces where space is limited. This versatility makes them ideal for robots, where form factor is often a constraint.

Embedding a frameless motor also eliminates the need for gearboxes and shaft couplings, which can introduce compliance or machine resonances into the motion control system. This helps ensure a tight, precise control loop with reduced overshoot and settling time. It also reduces maintenance by eliminating mechanical components that require regular attention.

Kollmorgen’s frameless motors are available in 17 standard sizes, each with multiple winding designs and stack lengths to provide the right performance for your application. You can choose a motor that is optimized for off-the-shelf harmonic gearing, achieving high torque density in the smallest possible form factor.

Frameless motors can be used anywhere that extremely high efficiency and precision are required in a compact, rugged package. They can be embedded into the machine structure to protect it from harsh environmental conditions, such as high-pressure washdowns. As a result, the machines that use them are lighter, smaller and more robust. They also require less maintenance because they use fewer components and are typically more durable than traditional motors.

High Torque Density

A key metric for electric motors is their torque density, which is the amount of power (in the form of electromagnetic force) that they generate per unit volume. While high torque density is a desirable trait for many applications, it can also be an elusive goal. In some cases, achieving high torque density requires the use of large stator and rotor dimensions, which can add significant weight and cost to the system.

Fortunately, there are solutions to the challenge of high torque density in small electric motors. One such solution is the airgap-less electric motor, an eccentric motor whose design has been modeled using electromagnetic finite element analysis. The model shows that the airgap-less electric motor leads the pack among induction and synchronous motors without permanent magnets in terms of torque density.

The high torque density of the airgap-less electric motor is achieved by combining several engineering and manufacturing techniques. These include using a flux barrier, a chamfered rotor rim, parallel windings and radially laminated cores to suppress losses.

In addition to enhancing torque density, the frameless motor can reduce maintenance costs by eliminating the need for couplings and belt adjustments. Furthermore, because the motor components do not include a housing, they can be easily installed within a mechanical design with slip-fit tolerances and commercially available industrial adhesives. This can save valuable machine setup time by eliminating the need for couplings and mechanical adjustments, as well as reducing system tuning and commissioning time.

Low Cogging Torque

A conventional motor is built into a housing or bolted to the machine it’s being used in, so it has a large mechanical structure that limits its power density. Frameless torque motors don’t have this limitation, so they’re able to achieve high torque densities without the additional weight and size of a shaft and bearings.

A frameless brushless motor consists of just the rotor and stator components that are mounted directly onto the machine’s structure. They don’t have a housing, shafting or bearings, so they can fit into tight spaces with minimal mechanical inertia and space requirements.

This design also opens up the possibility for a larger internal bore, which can be used to run cabling or optics inside the motor. This makes frameless motors Industrial rolling shutter door motor ideal for use in systems that require a lot of power in a small package, such as robotic joints, weapon stations and sensor gimbals for military applications.

Conventional motors, and even some well-designed slotless motors, suffer from a problem known as cogging torque. This is caused by the magnetic attraction between the magnets on the rotor and the iron teeth on the stator laminations. This can result in a “jerking” motion as the motor is rotated. Slotless motors don’t have this issue because they have no iron teeth.

At Allied Motion, we offer a wide range of standard frameless brushless motors from about 5 mm in diameter all the way up to our Megaflux 760 — which is 792 mm in diameter. For custom applications, we can work with you to create a bespoke frameless motor that will meet your specifications.

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