Rotary steerable drilling tool

The invention refers to a rotary steerable drilling tool having a tool collar and a bit shaft. The bit shaft is supported within the tool collar for pivotal movement about a fixed position along the bit shaft. Moreover, the rotary steerable drilling tool includes a variable bit shaft angulating mechanism, located within the interior of the tool collar. The variable bit shaft angulating mechanism includes a motor, an offset mandrel, and a variable offset coupling. The motor is attached to the upper end of the offset mandrel and adapted to rotate the offset mandrel. The upper end of the variable offset coupling is uncoupleably attached to an offset location of the lower end of the offset mandrel, and the upper end of the bit shaft is rotatably coupled to the variable offset coupling. The rotary steerable drilling tool also includes a torque transmitting coupling adapted to transmit torque from the tool collar to the bit shaft at the fixed position along the bit shaft. Finally, a seal system is adapted to seal between the lower end of the tool collar and the bit shaft.