Abstract: A differential drive mechanism comprises a cage (1), which is rotatable about an axis (3) and represents the input, two coaxial output shafts (12, which are rotatable in respect of the cage (1) about the axis (3), a coupling (4) which is connected eccentrically through two output shafts (12) to transmit relative contra-rotational movement between them by connections which permit relative rotation of the coupling (4) and the output shafts (12). The eccentric connection of the coupling (4) on the ouput shafts (12) includes a respective eccentric hole (9) in the inner end (10) of each output shaft (12) in which the associated end (6) of the coupling (4) is received. The ends (6) of the coupling (4) have a part-spherical engagement surface. A slipper (8) affording a complementary part-spherical internal surface is received in each eccentric hole (9) and each engagement surface is in engagement which a respective complementary internal surface.