Abstract: In this study, we designed an oil-filled motor that can be used at full-ocean depths, and investigated the friction losses caused by the rotating seal and the properties of the oil. The direct current (DC) motor is encapsulated in an aluminum alloy housing. A rubber diaphragm is used to balance the internal and external pressures so that the motor can work on the seabed without pressure difference. To study the resistance caused by the rotating seal, a numerical model of the Glyd ring and the rotating shaft was established. Results from a rotational torque test agreed with those from numerical analysis. The kinematic viscosity of four oils was measured at 1–25 °C. Oil bath experiments in an incubator showed that the resistance from oil is highly correlated with its dynamic viscosity. Dimethicone appears to be very suitable as an insulating oil for these motors. The working characteristics of the motor were tested in a high-pressure chamber. The results showed that the motor needs to overcome higher oil resistance under higher pressure. A prototype of a pressure-adaptive motor was designed and applied successfully in the hadal zone at a water depth of more than 10000 m.

Key words: Oil-filled motor; Full-ocean depth; Rotating seals; Friction loss; Viscous power; Sea trial

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