A crescent shaped separator is used on some ____ gear motors.

The crescent-shaped separator is specifically utilized in internal gear motors to help manage the flow of the hydraulic fluid within the system. Internal gear motors operate using a set of gears where one gear is fixed, and the other rotates and engages with the inner teeth of the fixed gear. The crescent shape acts as a divider that ensures proper meshing of the gears, creating distinct pressure pockets that enhance efficiency and minimize turbulence.

In this context, the design of internal gear motors leverages the crescent separator to optimize performance by improving the volumetric efficiency and managing the lubrication of the gears. This design characteristic is significant because it directly influences the motor's ability to generate torque and maintain operational stability. The other options do not utilize this specific type of separator in the same way; thus, the use of a crescent-shaped separator is characteristic of internal gear motors.