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Originally Posted by patTeam241
...However, I don't understand exactly where the benefit is, could someone explain this? ...
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As far as the benefits that planetary gears provide there are several:
1. The loading of the gears is reduced so smaller gears (lighter weight) can be used for the same torque ratings. Instead of having the power transmitted on one side of a gear to one side of another gear, the power is transmitted from several points, reducing the forces at any one point.
2. The overall effectiency of the gear system is greater then chains or belts.
3. The most useful benefit of planetary gears is planetary gears can also provide multiple gear ratios. Depending on which gear (or set of gears) is stationary you get different output speeds. for instance if you have the sun gear as the input, keep the planet gears stationary and the rotation of the ring gear is the output you get one speed. if you hold the ring gear stationary and allow the planet gears to rotate about the sun gear, and use that as the output, you get a different output. If you feed the output of one planetary set, into another planetary set you can have 4 different gear ratios. This method of changing gear ratios has the potential to save weight compared to the more conventional methods because there are no "extra" gears. Most of the multispeed transmissions i have seen at first swap gears in the transmission so that there is always atleast one gear that is not in use, and one that is extra weight not included in the planetary gear system.
4. Planetary gears sets also have the potential to take up less space, then conventional transmissions.
In summary planetary gears do the following:
1. reduce weight
2. increase efficiency
3. able to have multiple speeds
4. decrease size