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Thread: Changing out for a new gearbox...

  1. #1
    Associate Engineer
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    Changing out for a new gearbox...

    I'm looking for some advice on a gearbox and motor for my setup (I am new to motor/gear selection by the way). I've got a vertical lift, operated by a chain drive system. Right now I have a 1hp, 1700rpm motor connected to a 60:1 gearbox. Then there is a 32:13 gear externally. My problem is that the system is not capable of lifting the capacity that I need. The current gearbox says that it is rated for 0.75hp and has an output torque of 1670lb-in. By my calculations, plus a little extra, I am looking for about double the torque (about 3000lb-in).

    My solution is to use a gearbox that is actually rated for 1hp, which has a ratio of 100:1 and an output torque of 2900lb-in (I know it's not quite the 3000 that I was hoping for, but I at least want to know if I have the right idea). Then to keep a similar operating speed I would drop the external gear ration from 32:13 to something more like 19:13.

    Does this actually accomplish anything or does it put the overall performance of the system right back where it was to begin with?

    What effects will I see to the system if I do this?

    (links removed)...

  2. #2
    Principle Engineer Cragyon's Avatar
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    You need to back calculate for the motor torque / gear ratio required to get the job done. Then size the motor and gear box accordingly.

  3. #3
    Associate Engineer
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    Cragyon, Thank you. For some reason it clicked when I read what you wrote this time. I don't understand why.

    Followup question...... What are the implications or negative effects of putting a 1HP motor on a gearbox that's rated for .75HP input, like the setup that we currently have?

  4. #4
    Principle Engineer Cragyon's Avatar
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    In general, you are better off having a gearbox rated at a higher torque/HP than the motor. The gearbox will likely work however a failure early in use is high.

  5. #5
    Technical Fellow jboggs's Avatar
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    "Then to keep a similar operating speed I would drop the external gear ration from 32:13 to something more like 19:13."

    In doing so you are undoing all your work changing out the gearbox. Think about it. The load the motor sees does not come from the gearbox. It comes from the actual work being done, as "reflected" thru the gearbox and any other speed reducing devices such as sprockets. So, getting a higher ratio gearbox and then tying it to a lower ratio sprocket set ends up placing the same load on the motor.

  6. #6
    Associate Engineer
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    Thank you, both! I'll think back on this later on and cringe at how elementary this stuff is!

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