In the late 1950s, the original low-speed, high-torque hydraulic motor was developed from a fixed-rotor component of the oil pump. This component consisted of an internal ring gear and a matching gear or rotor. The inner ring gear is fixedly coupled to the housing, and the oil entering from the port urges the rotor to revolve around a center point. This slowly rotating rotor drives the output through a splined shaft into a cycloidal hydraulic motor. After the introduction of this initial cycloidal motor, after decades of evolution, another concept of the motor began to form. This motor has a roller mounted in the built-in ring gear. The motor with roller provides high starting and running torque, and the roller reduces friction, which increases efficiency even at very low speeds. Can produce a stable output. By changing the direction of the input and output flow, the motor is quickly reversed and produces equivalent torque in both directions. Each series of motors has a variety of displacement options to meet a variety of speed and torque requirements.