Design Methodology and Experimental Validation of a High-Efficiency Outer Rotor BLDC Motor for Electric Propulsion

This paper presents the design methodology, optimization, and experimental validation of a high-efficiency and high–torque-density outer-rotor brushless DC (BLDC) motor developed for electric propulsion applications. A systematic, efficiency-oriented design approach is proposed, focusing on slot/tooth dimensioning and multi-strand winding optimization to minimize copper and core losses. The optimized motor was analyzed using finite element analysis (FEA) and subsequently prototyped for experimental validation. To replicate realistic propulsion conditions, a novel propeller-based load test method was employed, enabling accurate assessment of efficiency and thermal behavior. The experimental results demonstrate 90% efficiency at rated power, closely matching simulation predictions. Thermal testing verified the robustness of the proposed design, demonstrating steady-state winding temperatures of 140 °C—approximately 60 °C below the insulation limit—at a current density of 16.6 A/mm², with thermally sustainable operation observed up to 22.1 A/mm² under forced-air cooling. The validated motor achieved a torque density of 4.08 N·m/kg, confirming its suitability for compact, lightweight, and high-efficiency aerial propulsion systems. The proposed methodology provides a scalable framework for developing high-performance BLDC motors in next-generation electric aircraft and drone propulsion platforms.