This paper presents an improved mathematical model of a single twisted string transmission system. The proposed mathematical model has been validated experimentally and provided a better match with the practical data in comparison to the conventional model. Translational transmission systems based on twisted strings coupled with electrical motors can compose light-weight, compact, and mechanically simple actuators which can be used in various robotic applications. Hands-on instructions on design of twisted string transmission systems presented in this paper are intended to help engineers in development of such actuation systems.