Small but mighty: How flat BLDC motors pack higher performance into a smaller footprint

DELTA LINE, a leading manufacturer of motion control solutions, offers a wide range of flat BLDC motors suitable for industries ranging from agriculture to medical devices, and we’ve now launched a series of flat motors with integrated encoders, for closed-loop control of position or speed.

The conventional design for brushless DC (BLDC) motors consists of a wound stator that houses the rotor with permanent magnets. But applications with strict space constraints make it challenging to fit a traditional BLDC motor without sacrificing performance. To address the need for high performance and compact size, Delta Line offers an alternative to the traditional BLDC motor – a series of brushless motors with a flat, or axially shorter, design that offers an exceptional power-to-volume ratio.

Flat BLDC motors are sometimes referred to as “external rotor” or “outer rotor” motors because their construction is somewhat opposite that of a traditional BLDC motor. In the flat, or external rotor, design, the rotor is the external part, and the stator is housed inside the rotor. This allows the motor to be axially shorter than a traditional motor, making flat BLDC motors especially ideal for applications where motor length is critical.

The outer rotor construction also provides several performance improvements over the traditional BLDC motor design. The most noticeable of these benefits has to do with the rotor size. For the stator to reside inside the rotor, the rotor in a flat BLDC motor must be larger than that of a conventional BLDC motor. The larger rotor means a larger air gap, which provides a larger “lever arm” for torque production. This means that external rotor motors can produce more torque than their conventional, internal rotor counterparts. Combine this higher torque production with the overall smaller motor size, and the result is unrivaled power density.

The flat, external rotor design also allows the motor to be constructed with a higher number of poles, which not only increases magnetic flux (further contributing to torque production), but also allows the motor to be precisely controlled at low speeds. And more poles, combined with the higher inertia of the larger rotor, reduces torque ripple, for extremely smooth operation.

A wide range of applications benefit from the smaller size, higher torque, and smoother operation of flat, external rotor BLDC motors – from large agriculture equipment to AGVs (automatic guided vehicles). Applications where flat BLDC motors are often the best – and sometimes, the only – choice are those that require high performance in an extremely compact size. Robot joints and handheld tools, in particular, benefit from the small form factor and excellent control at slow speed, where safety is paramount. And the extremely smooth torque production and good heat dissipation of flat, external rotor designs make them ideal for small medical devices such as pumps and powered air purifying respirators (PAPRs), where precise control and patient comfort are critical.

Delta Line offers flat, external rotor BLDC motors in sizes ranging from 20 mm to 90 mm, with rated torque up to 1 Nm. And we’ve recently introduced size 60 and 90 flat motors with integrated encoders, for applications that use closed-loop control for the highest levels of accuracy. The integrated magnetic encoder has 4096 CPR (counts per revolution) and can provide incremental or absolute feedback. With the integrated encoder, you get precise position or speed control without having to worry about additional components, integration, and setup efforts.