1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Pulleys connecting a motor and shaft - Determining loads in shafts

  1. Jun 3, 2010 #1
    1. The problem statement, all variables and given/known data
    A 5hp, 1755rpm, WEG Motor (part #00518OP3E184T) needs to turn another shaft that is 12" away at 1000rpm.

    2. Relevant equations
    T=F*r -> F=T/r
    Drive Ratio = Driver Pitch Diameter/Driven Pitch Diameter
    Sum Forces
    Sum Moments

    3. The attempt at a solution
    I plan on using a pulley (aka sheave) system with v-belts. I want to use a 8" sheave (7.95" pitch diameter) on the motor and a 14" sheave (13.95" pitch diameter) on the shaft that needs to turn 1000rpm. This will give me a Drive Ratio of .5714.

    1755rpm*.5714=1000rpm --- Which is what I want.

    My problem is, I don't know how to figure out the loads in the shaft. Since I know the torque in the motor (Torque = 5hp*5252/1755rpm=14.96ft*lb=179.52in*lb), I thought I might be able to figure out a force at a point on the motor sheave diameter by knowing that T=F*r so that F=T/r. However, when I do the calculations, I get that the force on a point on the outside of the sheave is F=179.52in*lb/(8in/2)=44.88lb. This sounds like too small of a force.

    I also think that that might not even be what I need. I think I need to figure out the tension in the v-belt? Basically I need to figure out how many v-belts I need (do I need just 1 belt or 2 or 3, etc.?), and the loads on the shaft that I need to spin at 1000rpm. If I can get the resulting loads on the shaft, I can figure out the type of bearings I need to support the shaft and such.

    I don't know where to go with this and could greatly use some help. Any help at all would be helpful. Thanks so much in advance.
  2. jcsd
  3. Jun 5, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hi MrBlue, welcome to the board. I'm not sure I understand the question. What class is this for? Is this a design problem that you're supposed to determine a design solution to? If so, to what degree do you want to extend this design solution? As you say, there are a number of issues to consider, such as drive ratio (you have that), shaft sizes for stress and fatigue analysis, bearing analysis, V-belt or other belt selection, part selection, mounting bases, belt tensioning device, etc... If you can clarify what you're expected to do I can probably help you out.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook