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PW_103146481-Visitor
1-Visitor
July 6, 2022
Solved

Obtain correct speed in MPH from RPM and tire dia.

  • July 6, 2022
  • 3 replies
  • 1759 views

I'm currently doing some calcs on the land-speed of a vehicle. From my other calcs, I obtained the wheel-motor's speed in RPMs, and the tire diameter. However, when attempting to obtain the speed from MPH, the calc seems way off. I did it by hand and used an online calculator. and they both gave the correct speed. What am I doing wrong, and how do I get the correct speed calc?

PW_10314648_0-1657118399452.png

 

    Best answer by PW_10314648

    PW_10314648_0-1657120466417.png

    I was able to figure it out. Here is the calcs for it. The diameter*pi calc in order to get the distance per rev needs to be done separately inside its own variable. I was trying to combine them in the "speed" function. Leaving this here for anyone else who comes across this problem.

     

    3 replies

    P
    PW_103146481-VisitorAuthorAnswer
    1-Visitor
    July 6, 2022

    PW_10314648_0-1657120466417.png

    I was able to figure it out. Here is the calcs for it. The diameter*pi calc in order to get the distance per rev needs to be done separately inside its own variable. I was trying to combine them in the "speed" function. Leaving this here for anyone else who comes across this problem.

     

    M
    MartinHanak24-Ruby III
    24-Ruby III
    July 7, 2022

    Hi,

    your problem is related to wrong use of rev unit.

    MartinHanak_0-1657183196375.png

     

    F
    Fred_Kohlhepp23-Emerald I
    23-Emerald I
    July 7, 2022

    The units "rpm" and "rev/min" have 2*pi radians included, so they refer to angular velocity.  The speed of the tread of the tire is radius times angular velocity, so:

    Fred_Kohlhepp_0-1657191856147.png

     

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