Differential drive mechanisms

A differential drive mechanism comprising:

• a cage (1) which is rotatable about a first axis (3) and represents an input,
• two coaxial output shafts (12) which are rotatable with respect to the cage (1) about said first axis (3), said output shafts each having an inner end (10),
• a coupling (4) which is connected eccentrically to the two output shafts (12) to transmit relative contra-rotational movement between them by eccentric connections which permit relative rotation of the coupling (4) and the output shafts (12) about an axis substantially parallel to said first axis (3), the eccentric connections of the coupling (4) and the output shafts (12) including a respective eccentric hole (9) in said inner end (10) of each output shaft (12), in which an associated end (6) of said coupling (4) is received, each end (6) of said coupling (4) having a part-spherical engagement surface,
• each eccentric hole being offset from said first axis in a direction of eccentricity,
• a restraint member (2) which is coupled to the cage (1) and to the coupling (4) such that the coupling (4) is rotatable with respect to the cage (1) about an axis substantially perpendicular to said first axis (3) and capable of reciprocating movement in a direction perpendicular to said first axis (3) but prevented from movement in a direction parallel to said first axis (3), and
• a slipper comprising two diametrically opposed pads (21) being received in each eccentric hole (9), each of said pads (21) having a part-spherical internal surface and being received in a respective recess (22) formed in a side wall of an associated eccentric hole (9), each engagement surface of said coupling being in engagement with the internal surface of each of said pads,
• wherein a shape of the eccentric holes (9) and an external shape of the slippers is such that rotation of the slippers relative to the output shafts (12) is prevented,
• wherein a portion of said inner end (10) of each output shaft (12) which defines the associated eccentric hole (9) and which is opposite to the direction of eccentricity (14) of the associated eccentric hole (9) is cut away.