A robotic surgical method comprises providing an instrument chassis having a proximal mounting section and a distal mounting section rigidly coupled to the proximal mounting section, an instrument guide assembly movably coupled to the distal mounting section, a pair of proximal actuators coupled to the proximal mounting section, and a linkage system operably interconnecting the proximal actuators and the instrument guide assembly. The method further comprises providing first control signals to one of the proximal actuators to cause the linkage system to move the instrument guide assembly in a first rotational degree of freedom, providing second control signals to the other proximal actuator to cause the linkage system to move the instrument guide assembly in a second rotational degree of freedom, and providing third control signals to the proximal actuators to cause the linkage system to move the instrument guide assembly in a third rotational degree of freedom.