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Need help figuring required horsepower of electric motor

  1. Feb 4, 2014 #1
    I have built a conveyor system but still need to power it. It is not a conveyor belt, but rather a trolley of sorts for moving materials up to the second floor. It runs parallel to stairs for about 17 or 18 feet in my garage at an angle of apx 38°. It needs to be able to move at least 500 lbs. but I would rather calculate it to accommodate more like 1000. It needs to move at a rate of about 105' per minute. It rolls on hard rubber wheels but I may switch to steel wheels. The motor will have a pulley on it which winds a high tensile strength material just like used for seatbelt material. I will be using a reversible motor with a speed of 1750 RPM and a reducer. I saw a 40:1 reducer available, so I made calculations based on it for my pulley. I came up with a pulley size of 9.14" in diameter and a circumference of 28.7". I know that with every wind the pulley will get larger, thereby increasing the speed, but it will be negligible for what I am doing. I know that there is friction loss here and there, and the exact speed of the motor may not be 1750, so once this is operational I may remake the pulley size up or down to my liking. I just need to know the HP requirements needed. My motto is "Overkill is underrated" so I would oversize the motor in a heartbeat, but I do not want to undersize it.
  2. jcsd
  3. Feb 5, 2014 #2


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    I assume 105' is 105 feet.
    The time needed will be (18 feet / 105' ) = 0.171 minutes = 10.28 seconds
    Up 18 feet * Sin(38°) = 11 feet vertical = 3.3528 metres.
    m = 500 pounds = 226.8 kg
    Potential Energy change = m*g*h = 226.8 * 9.8 * 3.3528 = 7452. joule
    That is 7452. joule / 10.28 seconds = 724.9 joule/sec = 724.9 W = 0.972 HP

    The absolute minimum motor would be 1 HP.
  4. Feb 5, 2014 #3


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    In English Units: ( to avoid metric conversions if you wish )

    1 HP = 550 foot-pounds/second

    500 pounds x 11 feet / 10.28 seconds = 535 ft-lbs/sec

    535 ft-lbs/sec / ( 550 ft-lbs/sec )/HP = 0.972 HP
  5. Feb 9, 2014 #4
    OK. Next question. If I use a 1 HP motor, and put a 40/1 speed reducer on it, does that just change the torque or the HP also?
  6. Feb 9, 2014 #5


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    Power = torque * RPM
    The gearbox is a transformer, it transforms the ratio of torque to RPM.
    The power does not change, apart from a couple of percent loss in the gearbox.
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