Motors and actuators used in harsh environments such as inside nuclear reactors must be water resistant, noncontaminating, radiation insensitive, and controllable over long distances. In general, pneumatic and hydraulic actuators can meet these requirements but support equipment may be bulky and complex. In addition, hydraulics require a special noncontaminating fluid.

But Turtle gearmotors from Extreme Robotics, San Jose, meet the same requirements while using simpler, less-costly support equipment. Turtle servogearmotors are available with 40-W brush or brushless motors and offer a choice of resolver, encoder, or tachometer motor feedback, all directly coupled to the output shaft.

Because resolvers do not use optical sensors, they are less sensitive to radiation than encoders, and can operate for a limited time in wet or condensed-moisture conditions, making them ideal for nuclear environments. Resolvers mount directly to the driveshaft, as opposed to the back of the motor, acting as a secondary position feedback device to improve position accuracy. Hall-effect sensors used for commutation provide primary position feedback.