Medical instruments having a translatable spool are disclosed. In one aspect, a medical instrument configured for use with a robotic system includes an instrument base configured to couple to a robotic drive mechanism of the robotic system and an elongate shaft coupled to the instrument base. The elongate shaft has a distal end. The medical instrument also includes a pull wire fixedly coupled to the distal end of the elongate shaft, the pull wire being configured to actuate the elongate shaft, and a rotatable spool in the instrument base. The rotatable spool is configured to direct the pull wire to the elongate shaft at an angle. The rotatable spool is configured to translate in coordination with actuation of the elongate shaft to control the angle of the pull wire relative to the elongate shaft.