Robotic instrument systems and control implementations are disclosed. In one such system, an elongate guide instrument such as a guide catheter includes tension or deflection element such as a stainless steel wire or pull wire. An actuator, such as a servo motor, is operably coupled to the controller. The controller is configured to control actuation of the servo motor based on execution of a control model including a mechanics model that accounts for a force on the guide instrument. The control model may also utilize both kinematics and mechanics models. The controller is configured to control actuation of the actuator based the control model that includes the mechanics model such that the elongate guide instrument bends when the actuator moves the deflection member.
