This machine is used to determine the efficiency of planetary gears and to study their rotational dynamics and the moment of inertia of each section, including gears and their fittings, using a high-accuracy angle sensor. The assembly measures the angular velocity and acceleration of each gear, the kinematic parameters of the system, and the corresponding moments of inertia based on the recorded data. Optocouplers positioned at four points of the apparatus measure the time interval for every 90˚ rotation of gears with high accuracy on the digital display. The apparatus incorporates two planetary stages, allowing users to obtain different velocity and output-shaft ratios by engaging the stages as needed. The gears are manufactured using the Hobbing method, which is one of the most reliable techniques for producing accurate involute profiles. Self-aligning couplings are used with the bearings to ensure proper shaft and bearing alignment while reducing noise, thereby minimizing calculations and efficiency errors. Additionally, rims with specified radii are installed on each stage; by attaching the hanger and precision weights, users can determine frictional losses and output efficiency of gears and compare the results with the theoretical predictions.