A robotic catheter manipulator includes a guide catheter including proximal and distal ends and lumen extending there through. A flexible bellows is secured at one end to the proximal end of the guide catheter and at the other end to a seal configured to receive a working catheter. In a loaded state, the working catheter is fixed relative to the seal. A ditherer is operatively connected to the seal for dithering the working catheter relative to the guide catheter when placed therein. The robotic catheter manipulator includes at least one force sensor for measuring the force applied to the working catheter by the ditherer. Force measurements may be translated into an estimated force that is experienced at the distal end of the working catheter which may then be displayed to the physician via a monitor or display.