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Automatic hydraulic jack -- choosing motor

  1. Apr 9, 2016 #1
    What type of motor can I use for this jack ?

    It's running from a 12V battery
  2. jcsd
  3. Apr 9, 2016 #2
    Something with a gear reducer? I got a funny image of the pump stroking 3,600 times a minute.

    If you're running off a battery then obviously a DC motor. You could use something like a digital fishing scale to determine the force required to push the handle down when the jack is under load. Working from that you could determine the minimum torque requirement for the motor. The slower the pumping rate the lower the required torque. You would also have to take into account friction of the drive mechanism, including the gear reducer. And, of course, you'd have to slot that pump rod.
  4. Apr 9, 2016 #3


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    That doesn't look like it'd stow conveniently in your car boot...
    Why reinvent the wheel? An off the shelf electric jack is about the same size as your bottle jack and they're not too expensive, certainly cheaper than the time and money to design and build your own.
  5. Apr 9, 2016 #4
    True, but we don't know why RedDevil is doing this. I'd like to know.
  6. Apr 10, 2016 #5
    I just thought of something else. The pumping stroke should occur when the effective pumping arm is the longest. That reduces the peak torque required.
  7. Apr 10, 2016 #6


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    Consider using a second hand 12V wiper motor from a car.
    It will have a reduction gear and crank as supplied.
  8. Apr 11, 2016 #7
    Unless you have a telescoping arm on the jack that design wouldn't work, and you would have to manually let the jack down. a scissor jack with a reversible electric motor straight shaft input attached to the jack itself would work much better.

    not sure how much you could lift or what size motor would be efficient for what ever application you are using it for but the design would give you a way to both raise and lower the jack with a flip of a switch.
  9. Apr 15, 2016 #8
    +1, w/o telescoping handle the jack or motor would need to be on a sliding mechanism. probably bad to have the jack slide back & forth ;)
  10. Apr 15, 2016 #9


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    Sliding mechanisms are usually quite inefficient unless they have captive linear ball races.

    A connecting rod would be a better method of connecting the crank to the jack arm. By selecting appropriate linkage dimensions and motor position, the motor torque could be optimised to the lifting part of the rotation cycle. A simple change to the jack handle socket would allow operation by horizontal motion rather than vertical.
  11. May 2, 2016 #10
    What if I just changed the connecting rod position to something like this

    Would it work ?
  12. May 2, 2016 #11


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    Have a look at bell crank mechanisms .
    Last edited: May 2, 2016
  13. May 2, 2016 #12


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    3 - Copy.jpg
    That looks like it would work, so long as the ends of the connecting rod were pins that would allow for the directional differences.
    Last edited: May 2, 2016
  14. May 2, 2016 #13
    How are you going to lower the jack?
  15. May 2, 2016 #14


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    I expect the pressure "release valve" that is wrongly labelled as “pressure relief” valve will be cracked open slightly.
  16. May 2, 2016 #15
    Yeah but the diagram doesn't show any automation for that. It would help to know its perpose....i have seen "jacks" rigged like this as a cheap way to make a dump bed on a pickup truck....its actually pretty cool. But it would be a pain in the kester to turn on the jack raise the bed then have to crawl under the truck to turn the pressure release just to lower the bed. Optimally i would opped for a system that both raises and lowers automatically. It really depends on the application of that jack.
    Last edited: May 2, 2016
  17. May 5, 2016 #16
    post #10, just make sure the diameter of the crank (I should say stroke) is less than the stroke of the jack piston handle where it connects to connecting rod. you can adjust handle length to accommodate, etc.
    Last edited: May 5, 2016
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