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Thread: advanced planetary gears

  1. #1
    Associate Engineer
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    Jan 2019
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    advanced planetary gears

    dont know where to post this question so if this is not the place please let me know where

    how would you work out the output of a planetary gear where the inner gears have a total bigger radius than the outer?
    say what would the output be with a gear set up of 2-1|2-1|2-5 starting with the driver, "|" meaning attached and "-" connected then 5 being the big outside gear
    i seem to get more than 1 output depending on things such as if outside gear is still or not..

    if the outside gear is moving its as simple to math as just a normal gear train 2*2*0.4=1.6 output for the example)

    but if you lock the outside gear i cant for the life of me work out the math >.> with a LOT of trial and error the example gives an output of 26.666~ but i got no clue how to use math to find that answer in a way that would work with different gear setups.. i did it by just rotating things in a 3d program till it lined up lol
    sdcfs.PNG

  2. #2
    Technical Fellow jboggs's Avatar
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    That is an intriguing gearset... but I don't see how it could work. When I mentally follow the motions at each interaction point it locks up. Won't move at all. Am I seeing it wrongly?

    It would work if the red gear were connected to the ring gear, but adding the green gear between the red gear and the ring gear reverses the action and locks it up.

  3. #3
    Associate Engineer
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    ya i was wondering if it would "lock up" or something lol
    so lets assume there was another gear there just to invert the direction? also i put the point at the wrong point so the output would be -2.666~

  4. #4
    Associate Engineer
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    again tho the question is whats the formula to work out why its -2.666~

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