In today’s model snippet of the day I post a first draft class diagram of an electric parking brake. The classes are rotor, caliper, gear box and motor. Attributes are placed such that the rotor has a diameter. The caliper is in a current_position. The gear box must have gears that provide a reduction. The motor has a power rating and generates a quantity of torque.
Although not shown, the motor and caliper have lifecycles defined by state machines. You can tell this because of the state machine glyph on the classes. The associations labeled R1, R2 and R3 relate instances of the classes together.
When the brake motor is activated it drives the gear box providing mechanical advantage through its reduction. The gear box closes the caliper changing its current_position. The caliper squeezes the rotor providing frictional forces to prevent the rotor from turning, and thus keeping the car in its parking space. Note that we can read the associations in the opposite direction and state that the rotor is squeezed by the caliper which is closed by the gear box which is driven by the motor.