[thatprogrammer]

You could set a time that only runs when the joystick to move the robot is moved beyond a certain point (0.1?), and when buttons for mechanisms are held. If your mechanisms are somewhat autonomous, you could set the timer to count when the motor controllers for these objects are set to .1 or higher.
Note: You can count the amount of times a piston is used and use a seperate timer for when the compressor runs.