Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mechanical System for Lifting and Lowering Weight

  1. Dec 16, 2011 #1
    Hi, I am looking for a 115 VAC motor (able to be plugged into an ordinary power outlet) that is capable of raising and lowering a load of up to 150 lbs. (attached to a cable and a pulley) at the speed of 6 inches per second. I want the speed to remain constant even if the load changes. How can I turn this into motor specifications? Also, given the low speed, will I need to use a gearbox with this motor and if so what could I use? Also anyone who could help me out in selecting/recommending parts for this system I would be eternally grateful. Thanks for any help.
  2. jcsd
  3. Dec 16, 2011 #2
    OK, here are a few starters:

    Compute the motor shaft power:

    Power = weight * g * vel

    weight = 150 lb
    g = acceleration due to gravity 9.81 m//s^2
    vel = velocity = 6 inch / sec

    watch your units.

    Now if you put a pulley of radius rp on the shaft, the angular speed is:

    angular speed pulley = vel / rp.

    If the motor nominal speed is: rpm_motor, the gear reduction is:

    gear reduction = rpm_motor / angular speed pulley.

    I would also recommend a small, low end VFD so you can tune the speed.
  4. Dec 18, 2011 #3


    User Avatar
    Gold Member

    Good answer, Edge.
    Just to simplify things, though... any normal 115VAC motor that I've seen runs at 1750rpm. That should eliminate one variable.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook