A planetary gearbox is a gearbox with the insight shaft and the output shaft aligned. 
A planetary gearbox is utilized to transfer the biggest torque in the most compact form (known as torque density).
The bicycle’s acceleration hub is a good exemplory case of a planet-wheel mechanism: Have you ever wondered how you can get so much power and capabilities in such a small hub? For a three-swiftness hub, a one-stage planetary equipment system can be used, for a five-swiftness hub a 2-stage. Each planet gear system includes a reduction state, a primary coupling and an acceleration mode.
In mathematical terms, the tiniest reduction ratio is 3: 1, the biggest is 10: 1. At a ratio of significantly less than 3, sunlight gear becomes too large against the earth gears. At a ratio greater than 10 sunlight wheel becomes too small and the torque will drop. The ratios are usually absolute i.electronic. an integer number.
Whoever invented the planetary gearbox isn’t known, but was functionally described by Leonardo da Vinci in 1490 and has been used for years and years.