Frameless motors are a type of electric motor that removes the housing, end bells, bearings and rotor shaft found in a housed motor. This allows for them to be integrated directly into a machine design and saves space.
The rotor and stator are designed to work as part of a complete servo system, with feedback devices such as incremental or absolute encoders or Hall sensors monitoring rotor position. This is what makes them so unique.
High Torque Density
Torque density is a measure of how much torque a motor can generate relative to its size and mass. It is one of the key factors to consider when choosing a motor for an application and can be used as a proxy for performance and efficiency.
In general, the higher a motor’s torque density, the more efficient it is. However, increasing a motor’s torque density comes with the additional challenge of achieving a balance between performance and physical limitations such as power losses and heat dissipation.
A frameless motor can offer a higher torque density than a traditional brush or permanent magnet brushed motor due to its lack of external components, such as shafts and housings. As a result, these motors can be integrated directly into a mechanical design for a more compact motion system.
Moog’s family of frameless motors includes 17 standard designs, with multiple stack lengths and winding options that allow them to be customized for your specific application. These frameless motor solutions, such as the ADR-P series of permanent magnet synchronous motors, are suitable for use in a variety of robotic applications and industrial automation tasks. They provide high slot fill factor and low cogging torque, while operating across a wide Frameless brushless motor range of DC voltages and speeds. The ADR-P series is also available in custom designs for a number of applications including; military, aerospace and semiconductor processing. In addition, these motors can be modified with materials to resist outgassing and radiation for hygienic applications, such as food and beverage production and packaging.
Minimal Inertia
When designing a system, engineers are often faced with constraints imposed by the motor, shaft and other components. With a frameless motor, these limits can be removed. Frameless torque motors are compact and lightweight, making them the ideal choice for systems requiring low inertia and high performance. Frameless BLDC motors can replace traditional power sources in applications such as robotic joints, weapon stations, sensor gimbals and UAV propulsion and guidance.
The moment of inertia of any shape is found by plugging values for height, radius and mass into formulas on the Moment of Inertia Table. When selecting shapes, engineers are looking for ones that minimize this value. In two dimensions, this is accomplished by finding the equilateral triangle that has the minimal moment of inertia.
Moog frameless (pancake) motors are available in a variety of standard designs and sizes, with several stack lengths and winding variations to meet specific performance needs. These models eliminate the design constraints imposed by the motor housing, shaft and connectors, allowing engineers to create highly compact applications.
Frameless motors can be used directly or can be integrated into compact, low-backlash planetary or harmonic gearing to deliver exceptionally precise performance. They also provide superior resistance to harsh environments, with a robust and durable housing that can withstand caustic washdowns, submersion and extreme temperatures.
Simple Installation
With no need for a motor housing, frameless motors can be directly embedded within the mechanical design of a system, reducing weight and size. Frameless motors can also be easily integrated with compact, low- or zero backlash planetary or harmonic gearing to provide precise speed and position control.
In addition, frameless motors feature Frameless brushless motor manufacturer a large bore diameter that can be utilized for cable management or optics mounting. This allows designers to eliminate external gears, belts and pulleys from the drive system, reducing power losses and allowing for a more compact motor package.
For those interested in adding encoders to their frameless motors, the option is available to use Hall sensors for position sensing. Hall sensors are an economical solution to add incremental position sensing to a system, and they can be used in place of or in conjunction with encoders.
Because frameless motors feature a hollow shaft, they are often designed with keyways to hold the rotor in place. Celera Motion does not recommend keys as a rotor retention method for several reasons including their high cost, requirement of axial clamping and ability to damage the rotor magnet when keyed. Instead, Celera offers a range of options for rotor retention, from a simple axial clamping to the option to mount magnets directly onto custom hubs without the need for an additional back iron ring.
Customization
Most electric motors come in a self-contained package with a rotor and stator assembled into some sort of housing. This makes them easy to integrate into larger machines by bolting the motor onto the machine’s frame. For some applications, however, it’s necessary to customize the motor for the environment. This can include special conditions like extreme temperature, vacuum, radiation or caustic washdowns. Fortunately, a frameless motor can be modified easily to meet specific environmental requirements.
Unlike traditional brushed DC motors, frameless motors can be integrated directly into a mechanical joint without any extra components like shaft couplings or bearings. This allows engineers to maximize torque density, weight and inertia while minimizing component complexity and size.
Moreover, frameless motors can be configured for direct drive or integrated with low- or zero-backlash planetary, harmonic or cycloidal gearing. Regardless, they can be instantly responsive to changing speed and position demands from the drive amplifier, resulting in unsurpassed precision. Engineers can also use the motor as an integral part of a servo system by including a feedback device (e.g., an incremental or absolute encoder, a Hall effect sensor or a resolver) to send information about the rotor’s location to the drive amplifier. This will fine-tune the rotor position to precisely match application requirements. The motor can also be fitted with a temperature sensor to monitor internal temperatures and prevent overheating for extended periods of time.
