The discussion centers on understanding the output speed of an epicyclic gearbox when the arm rotates at 100 rpm. It clarifies that the output shaft is connected to the second sun gear (S2), while the arm connects the planetary gears. When the arm is stationary at 0 rpm, a standard reduction occurs between the input and output. At 300 rpm, the system locks, resulting in the output shaft also rotating at 300 rpm. Therefore, the output speed at 100 rpm of the arm can be estimated to be one-third between the output at 0 rpm and 300 rpm.