Planetary gearboxes serve a major role in the mechanics of jacking system. Their purpose is to provide a mechanical advantage, i.e. to achieve a greater output force (to pinion) than the input force (from motor).
This is accomplished by converting the high speed of a hydraulic motor and its relatively low torque into a low speed but high torque. In layman’s terms, it’s a sacrifice of speed for the sake of gaining more power.
The gear set of a gearbox is composed of four integral components: the sun gear, planet gears, planet carrier, and ring gear.
The sun gear sits at the center. Orbiting around this central gear are the planet gears, held together by the planet carrier. The largest is the the ring gear, which is stationary and it encloses this system.
The input shaft from the motor connects to the sun gear, making it the driving gear. Driven by the sun gear, the planet gears turn the planet carrier, which is linked to the output shaft.
For an even higher gear ratio, additional gear sets can be added to the existing one. In this arrangement, the planet carrier (output) of the first gear set connects to the sun gear (input) of the second set, resulting in multiplied gear set ratios and a dramatically increased mechanical advantage. This is known as a multiple planetary gear set.
This was written on a jackup barge which had 68 gearboxes (4×17) with gear ratio of 374:1, allowing the elevation of 5000t weight.
If you want to learn more about gearboxes, watch the videos below.