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Gear RPM "img attached"

  1. Apr 6, 2016 #1
    Hey Guys,

    So in the attached image I'm trying to determine what the rpm of the 60 tooth gear will be given the 8.4" tire will be rotating at .68 rpm, everything else is just an assumption on my part.

    I'm assuming the following which is probably wong:

    The tire being rotated at .68 rpm will result in the .5" linked shaft rotating at 11.45 rpm. I'm dividing the circumference of the tire by the circumference of the shaft and multiplying by the rpm of the tire to arrive at 11.45 rpm.

    If the .5" shaft is rotating at 11.45 rpm for the purpose of calculations will the 60 tooth gear also be rotating at 11.45 rpm? Sorry, I obviously suck @ life.

    Last edited: Apr 6, 2016
  2. jcsd
  3. Apr 6, 2016 #2


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    Try this as a mental exercise.
    1) Put a chalk mark on the tire so you can tell when it makes on complete revolution. (Say at the top.)
    2) Put a mark on the shaft at the same place as the mark on the tire. (Again at the top.)
    3) Now turn the tire a quarter revolution.

    How many revolutions did the shaft make? Don't bother with any math, just think it thru.
  4. Apr 6, 2016 #3
    well, they both made a 1/4 revolution. So would this mean the shaft & gear is at .68 rpm? lol
  5. Apr 6, 2016 #4


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    Science Advisor

    Yup, you got it!
  6. Apr 6, 2016 #5
    Thanks man!
  7. Apr 9, 2016 #6
    Note that with a simple universal joint there will be some speed oscillation between the tire and the gear. Simple universal joints are not constant velocity. If that doesn't matter then the tire and the gear are turning at the same RPM. Everything, including the tire, the 60T gear, the intermediate shafts, the universal joint will be rotating at the same speed.
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