Structurally integrated brushless PM motor for miniature propeller thrusters

The design, analysis and performance of a brushless PM motor that is integrated in the structure of a miniature 50 mm diameter propeller thruster is considered; the stator is fitted in the faired thin duct that surrounds the propeller to improve its efficiency and protect it from damage, and the rotor is fitted to the rim of the propeller. Such a thruster is intended for use on small autonomous underwater vehicles that are being developed for defence, scientific and industry applications. Fitting a relatively large airgap motor with protective coating within the volume of a thin propeller duct (<10 mm thick) imposes extreme constraints on the dimensions of the machine, including a very thin rotor and stator radial thickness and relatively short axial length in addition to the relatively large airgap, which raises theoretical and practical issues that have not been considered in the literature. The design of such a machine is discussed, a demonstrator device is described and FEA and experimental results are reported.