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Calculate torque for gearbox

  1. Apr 14, 2015 #1
    I am designing a gearbox to take a human input with a crank 12 in. long attached to a shaft that drives the first gear which goes through a gearbox and eventually turns a motor shaft in case of electrical failure. This is for a class concept design. The motor has 5ft-lb of torsional inertia and I need to calculate the operator force.
    the gear box is set up with 4 spur gears, A,B,C, and D.
    A is a 30t gear, 3in diameter
    B is a gear with a big tooth and smaller gear attached to the top of it so that they both spin in the same direction at the same speed(see attached picture).
    B will have a 60t large gear attached to a 10t small gear with respective diameters, 6 and 1 inches.
    C is the same idea, the large is a 60t 6in. gear and the smaller is 30t, 3in.
    D will be a single spur gear with 20t, 2in.

    How do I calculate the torque or force that the operator must apply to the input shaft(the 30t gear, top left)

    Attached Files:

  2. jcsd
  3. Apr 14, 2015 #2

    jack action

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  4. Apr 14, 2015 #3


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    What is 5ft-lb of torsional inertia about? The units do not make sense. Mass moment of inertia should be in slug-ft^2 if you are working in USC units with feet for length.
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