To get used to planetary gears, it helps to be able to visualise how they move.
Ever pushed a box along on some sort of logs or tubes used as rollers?
Notice how the rollers always come out at the back?
Put a pencil between two CD cases and you can slide the bottom one left and the top one right the same distance, and the the pencil just spins on the spot.
These are effectively the sortof movements that planetary gears make. With the curvature of the earth, we could even argue that rollers are plantary gears. Oops sorry if there is any accidental pun, the earth being a planet and all that!
If you could put a camera on your planet carrier, you would see one aspect of the motion clearly. However much the sun moves left of the carrier, the ring gear must move right. eg 100 teeth of movement left by the sun gear is 100 teeth right by the ring gear. But 100 teeth might be once round a ring gear and twice round for a sun gear, so the number of rotations differs.
If you fix the sun or ring gear, the roller analogy makes it easy to visualise.If you fix the planetary carrier, the CD box analogy makes it easy to visualise.
More complex motions are just combinations of the two.
Another easy motion to visualise is imagining the whole thing welded together. So regarless of number of teeth, it is possible to rotate the sun, ring and planet carrier equally.
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From the roller analogy [imagine a fixed floor], you can see the rollers never move as far as the box. (The rollers move half as far.) Restated, the box moves further than the rollers. In Brian Peterson's more correct terminology ....
ANY input from the carrier with either the sun or ring locked, will drive the remaining element in "overdrive", faster than the input.
If I've managed to be of any help, maybe you can see that for yourself now. If not I could post some MPEG videos. One picture is worth 100 of my words, for sure. (bit of work involved so I am reluctant to do it.)
Is there any sort of "final drive" on your application that can be changed. Plantary gears are much easier if one of the ratios is 1:1 - the everything welded together anaology, ie the planet gears don't turn.
With VERY small planet gears, then like a box on rollers moving twice as far as the rollers themselves, a sun gear or ring gear could move about twice as far the planet carrier - a bit more or less in practice, depending on whether you used the sun or ring.
Then with a final output of 3/4 of that you'd have 1.5 times your speed (2 * 3/4 = 1.5). Or with everything rotating like locked together you'd simply have the output rotating 3/4 the speed of the input.
