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Thread: Geared Motor - Torque requirements

  1. #1
    Associate Engineer
    Join Date
    May 2021
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    Geared Motor - Torque requirements

    I'm trying to choose a 12vdc geared motor for a TV lift system for an RV. It's mounted in an overhead drawer.

    I'm an ME but I've never had to deal with motors or the physics involved. I've done a little research and reviewed the principles but I'm not sure about my results or the method I've used to get there.

    Am I missing any dynamics on the profile of the lift? I'm seeing it as a pivoting diagonal lift? Are motors rated by a straight vertical lift? Because it's a hinged lift, will the lift angle make any considerable difference in my torque requirements?

    Can anyone tell me if I've gone wrong or missed anything?

    Formula used: τ[Nm]=(mass[kg] g) pulley radius[m]

    TV mass = 4.5kg
    g = 9.81
    Pulley radius = (12mm dia / 2) = 6mm / 1000 = .006m

    τ[Nm]= (4.5 x 9.81) x .006

    τ[Nm]= .26487Nm (264.87mNm or 2.7kgf cm)



    Motor I've chosen based on 2.7 kgf cm:
    RPM = 40
    Rated Torque = 5.6 kg.cm
    Max Torque = 24 kg.cm
    Ratio reduction = 150
    No-Load Current (ma) = ≤60
    Rated Current (A) = ≤0.6
    Stall Current (A) = 1.3

    Here's the drawing. Note: the pin point is attached to the drawer.

    TV.jpg

  2. #2
    What you are dealing with is called overhung load. This pdf should explain it much better than I can.

    Gearmotor Sizing Guide.pdf


    Great drawing but I am not certain how the raising/lowering is taking place (winding a cable?). You may have to change the driver or driven pulley to get the speed right. If you want to have easy speed change look into DC drives. Cheap and easy.

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