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Homework Help: Epicyclic gearing: 3 free axes

  1. Dec 16, 2014 #1
    1. The problem statement, all variables and given/known data

    The teacher said it is possible to use an epicyclic gearing with no axis fixed but nobody use the gearing like that. I watched this video:

    at time 42s it's possible to watch it. I have 2 questions:

    1) Is it possible to used the epicycloidal train with no axis fixed ?

    2) If yes, what is the ratio of reduction ? is it dependant of the torque ?

    Maybe if you have a link ?

    2. Relevant equations


    3. The attempt at a solution

    I'm looking for this case, but each time the epicyclic gearing is used with one fixed axis.
    Last edited: Dec 16, 2014
  2. jcsd
  3. Dec 16, 2014 #2


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    Staff: Mentor

    I don't see an argument against it.

    You have to consider all three rotations at the same time. Things like a ratio of reduction that consider only two do not make sense any more. That's probably the reason they are not used in that mode.
  4. Dec 16, 2014 #3
    I can set the input to the sun gear and the output to the ring gear (planets are free to turn like they want) ? Why there is no a ratio ?

    In this case, it's possible to reduce a rotational velocity without give a torque on the support ?
  5. Dec 16, 2014 #4


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    Staff: Mentor

    Then your output will not get any torque (neglecting friction). The free axis will rotate with the right speed to give zero output power.
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