A planetary differential employs a longitudinal shaft having a restricted portion at least two balls directly engaging the longitudinal shaft at said restricted portion forming an inner race. The differential includes further an outer race having a taper engaged by the balls and a cage for the balls. A first rotary input is provided to one of the inner race, outer race, and cage. A secondary rotary input is provided to another of the inner race, outer race, and cage. A rotary output is provided to yet another of the inner race, outer race, and cage. The inner race and outer race are mounted for rotary movement.A servo system, including the planetary differential, is also disclosed.