What is a planetary gearbox?
Which millennium-old tech basics are some of the most innovative technological breakthroughs of the moment? Robotics, 3D printing, and new modes of transportation have one thing in common: often, they are driven by a planetary gearbox.
As suppliers of planetary gearboxes, of course, we know all the ins and outs, but what if you encounter this technology for the first time? We have decided to explain it clearly for everyone – in this article, we discuss the basics of planetary gearboxes.
What is a planetary gearbox?
A planetary gearbox, also known as epicyclic gear box, comprises three types of gears — sun gear, planet gears and a ring gear and the gearbox has an input shaft aligned with the output shaft. The planet gears are mounted on a moveable carrier, and they rotate around the sun gear, which is positioned at the centre. The planet gears rotates around the sun gear and mesh with an outer ring gear. The three gears rotate in tandem within the planetary gearbox to make a stage. When required, more stage can be added to the gear system for higher ratios. The planetary gearbox's basic function is to transfer the maximum quantity of torque with the least quantity of space. The process of the gear includes a reduction mode, an acceleration mode, and coupling.
Depending upon application, planetary gearboxes vary from very simple to intricate compound gear systems. Compound planetary gearboxes have significant plus such as higher torque to weight ratio, larger reduction ratio, and more flexible configuration.
Planetary gearboxes are a gearbox with the input shaft and output shaft aligned. Planetary gearboxes are used to transfer the greatest torque in the most compact form known as torque density. The acceleration hub of a bicycle is a great example of a planetary-wheel mechanism: have you ever wondered how you can get so much power & efficiency in such a small hub? For three-speed hubs, a one-stage planetary gear system is used; for five-speed hubs, a 2-stage.
Each planetary gear system has a reduction position, direct coupling, and acceleration mode. In mathematical terms, the smallest reduction ratio is 3:1; the largest is 10:1. At a ratio of less than 3, the sun gears become much larger than the planet gear.
At a ratio greater than ten, the sun wheel becomes too small, and the torque will drop. Ratios are usually absolute, i.e., integer numbers. Who invented the planetary gearbox is not known, but it was functionally described by Leonardo da Vinci in 1490 & has been used for centuries.
Why is it named a planetary gearbox?
Planetary gearboxes got their name because of how the different gears move together. In planetary gearboxes, we see sun gear gears, satellite ring gears, and two or more planetary gears. Normally, the sun-gear operates and thus moves the planetary gear locked in the planet carrier and forms the output shaft. Satellite gear has a fixed position with respect to the outside world.
It looks very similar to our planet's Solar System, and that's where the name comes from. What helped is that ancient gear constructions were widely used in astrology for mapping & following our celestial bodies. So it was not such a bigs step.
In practice, we often speak from the point of view of the use of planetary gearboxes for industrial automation. That's why we call sun gear the input shaft, planet gears and carrier as the output shaft, and satellite gear or ring gear as housing.