ROCKING INSTABILITY OF A PULLED SUITCASE WITH 2 WHEELS

Rocking motions of a two-wheeled suitcase are considered. The suitcase is pulled on a horizontal ground and may rock back and forth, first w ith one wheel in contact with the ground, then the other, and so on. W hen a wheel impacts the ground, some energy is lost. It is assumed tha t the puller's walking motion induces a periodic force or moment on th e handle of the suitcase. In addition, the puller may apply an additio nal restoring moment in an attempt to suppress the rocking motion. Und er certain conditions, the motion may grow until the suitcase overturn s. The effects of the excitation frequency and the coefficient of the restoring moment on the critical excitation amplitude are examined for the special case in which yaw and pitch motions are neglected and the suitcase is pulled in a straight line. Due to the nonlinearities of t he problem, the results exhibit some irregular behavior.