A traction drive system for an articulated robotic arm. The traction drive system can include an input drive disk, a spider, an array of traction balls, a traction plate, an output drive shaft, a clamping device to load the traction balls, and an absolute rotation position sensor system. The rotation of the output drive shaft can be coupled to the rotation of the input drive disk while the traction balls are frictionally engaged to the drive disk surface and traction plate surface. The rotational connection can be decoupled when the traction balls are not frictionally engaged to the drive disk surface and traction plate surface. A rotational position sensor located in proximity to the traction drive can provide absolute rotational position feedback of the output drive shaft.