In this paper, we propose a method to efficiently design joint motors, which are the key elements that drive a cooperative robot. Designing joint motors with more power than the required capacity increases the volume and weight of the robot. On the other hand, designing joint motors with less power than the required capacity can lead to failure and safety accidents because of high temperature rise and mechanical instability. Therefore, in this study, the required capacities of the joint motors were determined through a dynamic analysis of the robot system and incorporated in the joint motor design specifications. An electromagnetic analysis was performed during design using the two-dimensional finite element method, and the detailed dimensions of the motor were determined using the response surface method, which is an optimal design technique. The thermal characteristics of the joint motor were evaluated using a thermal equivalent circuit. The designed joint motors were manufactured, and their performance were tested not only at the component level, but also at the robot system level to verify experimentally the validity and usefulness of the proposed joint motor design method.