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  • Working out epicyclic gear ratios.

    I've been checking out this site and I'm struggling to understand the formulas, could someone run me through it please?

    http://www.roymech.co.uk/Useful_Tabl...lic_gears.html

    I have an epicyclic gearbox that I want to figure the ratio for. It looks like exapmple 1 on that page. On my gearbox, S is the input shaft, L is the output and A is fixed.

    Input gear S has 9 teeth
    Planet gears P have 17 teeth
    Annular gear A has 45 teeth.

    From turning the input and watching the output I can see my ratio is about 6:1



    I have another which is much lower geared and has the following values:

    S=8
    P=28
    A=64

    What formula should I use?
    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

  • #2
    If you are using the setup in fig 1 then ignore the planets, they are only idlers.

    The formulae is Ring / Sun +1 so 45/9 +1 =6:1

    Your other ratios will be 64 / 8 = 8 +1 = 9:1

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      Thanks John. I don't understand why they couldn't put that formula on the page I linked to

      This gearbox is stacked with two 6:1 ratios and a 9:1 so I could have 6:1, 36:1 54:1 or 324:1.
      Peter - novice home machinist, modern motorcycle enthusiast.

      Denford Viceroy 280 Synchro (11 x 24)
      Herbert 0V adapted to R8 by 'Sir John'.
      Monarch 10EE 1942

      Comment


      • #4
        Yes I read the page and then reached for another book, even after reading what the formulae was that page still made no sense to me.

        I think the phrase "Educated beyond the ability to understand" comes to mind

        .
        .

        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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