A gearbox for driving a driving element (112, 113) of a roller-based- drive system (110, 210, 310, 410), the gearbox comprising: a gear train; and an output shaft assembly positioned between the gear train and a power output end of the gearbox, the output shaft assembly including, a first shaft segment extending to the power output end, a second shaft segment coupled to the gear train, a torsion spring interposed between the first shaft segment and the second shaft segment; wherein, upon non-conjugate meshing of the driving element (112, 113), the torsion spring expands and contracts so that the angular velocity of the second shaft segment differs from the angular velocity of the first shaft segment characterized by the annular surface of the second end of the torsion spring coupled to the second shaft segment with at least one key, the gearbox further comprising: a spring-load limiting system, which system includes; a flange of the first shaft segment; and at least one slot in the flange; wherein the at least one slot surrounds a portion of the at least one key; wherein the at least one slot is larger than the at least one key; wherein the at least one key is engageable with a side of the at least one slot upon occurrence of a predetermined rotational displacement of an end of the torsion spring, and wherein, upon engagement of the at least one key with the side of the at least one slot, a torque-transmission path develops, which torque-transmission path bypasses the torsion spring and passes from the second shaft segment directly into the first shaft segment. a gear train; and an output shaft assembly positioned between the gear train and a power output end of the gearbox, the output shaft assembly including, a first shaft segment extending to the power output end, a second shaft segment coupled to the gear train, a torsion spring interposed between the first shaft segment and the second shaft segment; wherein, upon non-conjugate meshing of the driving element (112, 113), the torsion spring expands and contracts so that the angular velocity of the second shaft segment differs from the angular velocity of the first shaft segment characterized by the annular surface of the second end of the torsion spring coupled to the second shaft segment with at least one key, the gearbox further comprising: a spring-load limiting system, which system includes; a flange of the first shaft segment; and at least one slot in the flange; wherein the at least one slot surrounds a portion of the at least one key; wherein the at least one slot is larger than the at least one key; wherein the at least one key is engageable with a side of the at least one slot upon occurrence of a predetermined rotational displacement of an end of the torsion spring, and wherein, upon engagement of the at least one key with the side of the at least one slot, a torque-transmission path develops, which torque-transmission path bypasses the torsion spring and passes from the second shaft segment directly into the first shaft segment. a spring-load limiting system, which system includes; a flange of the first shaft segment; and at least one slot in the flange; wherein the at least one slot surrounds a portion of the at least one key; wherein the at least one slot is larger than the at least one key; wherein the at least one key is engageable with a side of the at least one slot upon occurrence of a predetermined rotational displacement of an end of the torsion spring, and wherein, upon engagement of the at least one key with the side of the at least one slot, a torque-transmission path develops, which torque-transmission path bypasses the torsion spring and passes from the second shaft segment directly into the first shaft segment.