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Gear ratio calculation question

  1. Sep 1, 2005 #1
    I have a scooter with a 5 inch diameter wheel and I want to make it go 25mph with a motor that has this specs.
    ====
    Power 0.35 hp @12v 1.43 hp @24v
    Torque 0.47 lbf*ft @12v 0.97 lbf*ft @24v
    Efficiency 70% @12v 76% @24v
    Speed 1260 RPM / Volt
    Voltage 12 volts or 24 volts*
    Weight 11 oz.
    Output Shaft 5mm dia x .75" long
    Diameter 1.7"
    Length 2.8" (from face)
    Face Mount 2 M4 holes 1.14" apart
    ===
    I use this equation to figure out the RPM of the wheel for 25mph.
    RPM*(((D*3.14)/12)*60)/5280)=MPH
    Calcuated RPM for 25mph is = 1680 RPM

    i'm planning to use 17 volts, thus the motor rpm would be 1260*17=21420 RPM

    Now i'm finding the gear reduction. 21420/1680= 12.75
    5"/12.75 thus .39" is the required gear size that is attached to the motor.

    Is the .39" gear size the diameter, radius or circumference???

    i'm not using a sprocket because it is friction drive.

    Are there any potential problems with this setup? Is my calculation correct?
     
    Last edited: Sep 1, 2005
  2. jcsd
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