A robot arm assembly a base unit with a shoulder assembly rotatably disposed on the base unit. A lower robot arm is pivotably attached to the shoulder assembly. An upper robot arm is pivotably attached to the lower robot arm. The base unit includes a first motor which rotates a main shaft fixed to the shoulder assembly to rotate the shoulder. A second motor in the base unit rotates a second shaft in the shoulder assembly extending through the main shaft to pivot the lower robot arm with respect to the shoulder.