In-pipe robots require friction on the wheels to maintain traction. Ability to vary this friction is highly desirable but conventionally used linkage mechanism is not suitable for it. This paper presents a novel mechanism that generates controllable friction with minimal energy for in-pipe robots. Details of how the mechanism uses permanent magnets to achieve the objective are discussed. A simple but appropriate model of a permanent magnet is also presented for the analysis. The paper identifies the important design parameters, and more importantly establishes the relation between the design parameters and the system’s performance. In addition, a prototype of the mechanism was designed, fabricated and tested for validation. The experimental results agree well with the predicted behavior through simulation and demonstrate the effectiveness of the mechanism.