Development and Evaluation of Pressure-Tolerant Stepper Motors for Underwater Robotics Applications

The present paper describes the approach to adapt commercially available NEMA17 stepper motors to make them suitable for long-term underwater use. The resulting subsea actuators are intended to provide a user-friendly and cost-effective alternative to hydraulic systems and servo motors for basic robotic applications. As part of the investigations, the motor requirements are identified based on an application example and a sufficiently dimensioned standard motor is selected for conversion. The necessary adaptations are then discussed, and the production of three prototypes is documented. Measurements are performed with regard to torque and angular accuracy to compare the performance of the prototypes with an unmodified benchmark motor. Finally, the results of the investigations are discussed and summarized. From the results, it can be concluded that a promising conversion approach for the production of subsea stepper motors was found. In terms of torque and angular accuracy, it can be stated that the modified motors reliably deliver output torques of more than 0.2 Nm and remain precisely controllable at low speeds of 10 rpm. However, due to a prototypical manufacturing process, some errors still lead to corrosion problems. These issues are identified and documented to improve the manufacturing process.