The construction of a brushless motor can influence its behavior just as much as its electrical rating. Outrunner and inrunner BLDC motors use different arrangements of the rotating and stationary components, resulting in different mechanical characteristics. Neither design is universally better because the appropriate configuration depends on the required combination of speed, torque, dimensions, cooling, and mechanical integration.

Inrunner motors generally place the rotating assembly inside the stationary stator, while outrunner motors use a rotating outer section around the stator. This difference can affect the motor's speed characteristics, torque production, and physical arrangement. The choice should therefore be based on the actual operating requirements instead of assuming that one structure is suitable for every brushless motor application.

Feedback configuration provides another distinction. Sensored brushless motors can use Hall sensors to determine rotor position, which can be useful for controlled starting and low-speed operation. Sensorless BLDC motors use electronic estimation methods and may provide a simpler physical design when position sensors are not necessary. The control requirements of the equipment should determine which approach is more appropriate.

Other structural variations can address specialized requirements. Frameless brushless motors can be incorporated directly into mechanisms where a conventional motor housing would create unwanted size or weight, while waterproof designs can provide additional protection for equipment exposed to moisture. Different NEMA frame sizes and shaft configurations can also help engineers adapt a motor to standardized or customized mechanical systems.

Understanding motor structure allows designers to look beyond basic voltage and power specifications. When speed, torque, feedback, dimensions, environmental protection, and installation requirements are considered together, the differences between BLDC motor configurations become useful tools for matching a motor to a particular machine without limiting the technology to one type of application.