This paper present an experimental characterization of a planetary gearbox designed at LARM. A new test bed, which consist of an AC motor coupled to the gearbox to drive a mechanical load, was worked out in order to analyze the differential operation stage of the planetary gearbox by means of setting a varying load. The test bed was instrumented with different mechanical and electrical transducers in order to register the transient response and compute a better characterization of the dynamic system performance. Tests at constant operation speed and varying load were developed. Vibration and torque were measured in the input and output gearbox shaft, meanwhile the vibrations on the load shaft and the current consumption of the motor drive were also registered.