Motion analysis of a bicycle rear derailleur during the shifting process

This paper presents a comprehensive theoretical and experimental investigation into the motion characteristic of the guide pulley of a typical rear derailleur during the shifting process. This characteristic can serve as a performance index of precise engagement and smooth shifting and can also be specified during the design stage. By observing the phenomenological behavior of the principal elements of the derailleur, a four-mode mathematical model was developed to illustrate the motion characteristics of the guide pulley during the shifting process. The equations governing the motion of the guide and tension pulleys were derived by using Lagrange's method. These equations were then employed to predict the motion characteristic of a derailleur as it shifted at different cycling speeds. Finally, an experimental rig was constructed and the motion of the guide and tension pulleys was measured using two encoders mounted on the shaft of each pulley for verification. This study provides a scientific basis for the systematic design of derailleurs and the related components, such as the spring constants df the B and P springs, the tooth profile of each sprocket, and the configuration of the changer mechanism which keeps the guide and tension pulleys moving along the designated path to guarantee precise and smooth shifting. (C) 1997 Elsevier Science Ltd. All rights reserved.