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Originally Posted by sanddrag
The main benefit is lots of reduction in a relatively small space while keeping the output shaft on the same axis as the input. Take for example the globe motor. Do you have any idea how large of a reduction is in that tiny planetary gearhead? Something like 115:1. Try to do that with spurs in that amount of space.
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I did something similar in 2004 with swerve drive, having the gear reduction inside the wheel. But I have to ask, why planetary? It costs much less to just use external gears, instead of internal gears. The only thing you dont get anymore with one reduction is the axis of the drive shaft is no longer on the same axis as the wheel. So just use two reductions. I did in the swerve I designed, and it was very spiffy. In fact, people were asking if it had a planetary reduction in it, but it didnt. It was very similar, used a lot less gears, and a lot less bearings. With a reduction of 1:42.
If you look at the link to the concept sanddrag posted, you can tell that the gear reduction in the planetary is just the teeth of the sun gear over the teeth of the internal gear. Why not just make the external gear an internal gear? Solves a lot of problems. But hey, I can understand if you're doing it beacuse its awesome. It is. Having planetary gears reduces the stress on all the gears because more teeth are in contact at the same time. It's a cool idea, I just want you to be aware that it is more costly than several very similar alternatives.