The DC motor driver offers substantial flexibility to apply to other mechanical applications as long as motor current is within the current limitations of the motor driver IC. The LED sensors can be replaced with 5K potentiometers to vary the motor control, one pot can be actuated from the motor shaft for position feed back while the other pot sets the position. Tachometers work with changes to the program.
A two axis solar tracker is easy to create if a picaxe 18 or 20 is implemented, the code is about the same just check the routine to initialize the ADC pin and redefine the output ports and associated pins to your requirements. To prevent burnout while testing, substitute 2 back to back LEDs for the motor while testing.
This circuit needs modification for stepper motors and non modified RC servo motors but its all very easy.