The current invention provides an automatic gear-shift drive mechanism including a first gear system having a first gear ratio, and a second gear system having a second gear ratio, wherein the first gear ratio is higher than the second gear ratio, and is biased to spin the drying assembly with the first gear system when the automatic gear-shift drive mechanism is driven and the workload is below a threshold workload, and switch to spin the drying assembly with the first and the second gear systems when the automatic gear-shift drive mechanism is driven and the workload is at or above the threshold workload.
