Presented is a roller shade system that includes a flexible shade material having a lower end, a rotatably supported roller tube that windingly receives the shade material, a stepper motor that operably engages the roller tube to rotate the roller tube to move the lower end of the shade material between a first position and a second position, an optical sensor configured for capturing an image frame of the shade material at linear positions along the shade material as the lower end of the flexible shade material moves from the first position to the second position, and a stepper motor controller configured for controlling the frequency of input pulses to the stepper motor to move the lower end of the flexible shade material from the first position to the second position at a substantially constant linear velocity in response to position information obtained from the plurality of captured image frames.