I have a question for all you vending machine designers out there. Why the long wait for change?
You feed 2 bucks into the bill acceptor and punch in the letter C and the number 4 for the 20oz Diet Dr. Pepper. You watch as the as a little bucket on an arm moves smoothly up and over until it stops under the appropriate slot. The row of bottles is pushed forward, forcing the front one off the ledge where it drops the 6″ into the bucket. The arm then glides over to the left and then (in this case) drops down until top edge of the bucket catches on the ledge above the dispensing chute. This allows the Diet Dr. Pepper to slide down into holding area and then rests for a second until the round plexiglass door rotates 180° until the drink is exposed and you can pick it out. With your selected drink now in your hand, the round door rotates back sealing off the dispensing area. A few seconds later 75¢ in change plops down one quarter at a time. Elapsed time between picking a selection and receiving the change is probably 30 seconds.
The only thing I can think of for making you wait is so that your attention is not diverted from watching the nifty dispensing dance.