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Homework Help: Simple gear train, typo?

  1. Dec 18, 2017 #1

    EastWindBreaks

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    1. The problem statement, all variables and given/known data
    upload_2017-12-18_6-8-28.png

    2. Relevant equations


    3. The attempt at a solution
    if you do 38*25/pi , you would get 302.394 for the exact pitch circle diameter, similarly, exact d2 should be 907.183 mm, is it a typo? or did I miss something?
     
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  3. Dec 18, 2017 #2

    CWatters

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    The used a slightly different value for pi. Probably 3.142
     
  4. Dec 18, 2017 #3

    EastWindBreaks

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    the new exact d1 should be T1*Pc/pi, correct? but it has only Pc/T1
     
    Last edited: Dec 18, 2017
  5. Dec 18, 2017 #4

    CWatters

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  6. Dec 18, 2017 #5

    EastWindBreaks

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  7. Dec 18, 2017 #6

    EastWindBreaks

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  8. Dec 19, 2017 #7

    CWatters

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    You can have a single stage with a bigger ratio but I think there are frequently better options, eg a multi stage might be smaller or have less wear. Im not a mechanical engineer but I think single stage spur gears for power transmission are normally limited to somewhere under 10. Some sites say under 7. The issue is with the small gear, where I think the practical minimum number of teeth is around 20 teeth.

    Technically a rack and pinion has an infinite ratio.

    Some tower cranes have a small pinion turning a very large ring gear under the cab and I think the ratio there might be more than 20. That's in addition to a sealed gearbox between the electric motor and pinion.
     
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