Motor Power Selection and Transmission Ratio Distribution for Mechanical Drive Systems under Constant and Variable Loads

This document presents a systematic procedure for motor power selection and transmission ratio distribution in mechanical drive systems operating under constant and variable loads. For constant-load operation, the required motor power is determined from the power required by the working machine and the overall transmission efficiency. For periodically varying loads at approximately constant speed, an RMS equivalent-load approach is introduced to determine the equivalent power and the required motor rating. The preliminary motor selection is subsequently verified against the maximum required load, permissible overload duration, maximum torque, duty, and starting requirements. After motor selection, the overall transmission ratio is distributed among the individual transmission stages, and the power, rotational speed, and torque at each shaft are determined. Two conveyor-drive examples are presented to illustrate the procedure: a constant-load system employing a V-belt drive and a single-stage helical gear reducer, and a variable-load system employing a two-stage gear reducer and a chain drive. The examples demonstrate the distinction between RMS-based motor thermal selection and the loading criteria required for subsequent transmission-component design. The proposed procedure provides a consistent framework for selecting electric motors and determining transmission parameters in mechanical drive-system design.