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  • Ball screw / motor specification

    Discussion in 'Calculations' started by Pete, Nov 4, 2009.

    1. Pete

      Pete Well-Known Member

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      Hi all,

      In a nutshell:
      What spec motor do i need to use to lift 8000N vertically using a ball screw?

      and/or

      Is the a conversion of motor power torque etc to linear force?

      The long winded version:

      I'm currently designing a mobile patient hoist, and I want it to have a 150mm diameter circular telescopic mast.

      The hoist will lift 200kg (1962N load) at the end of a boom. So the force required by the telescopic mast to lift the load will be in the region of 8000N.

      Still with me?

      I want to put a mechanical actuator inside the mast to provide the lift, but am struggling to find any linear actuators which have the motor in-line rather than at 90 degrees.

      So, I’m thinking, is it possible for me to source a separate ball screw and motor and make my own?

      And if so, how do i go about working out what sort of spec the motor should be to lift such a weight.

      And would such a motor actually fit inside a 150mm diameter tube?

      Enjoy!
       
    2.  
    3. matt_decat

      matt_decat Member

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      Any chance of posting some sort of diagram to help visualize the situation, doesn't have to be as good as a Picasso painting, just good enough to understand the situation.
       
    4. mvalenti

      mvalenti Well-Known Member

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      Silly question comming.... Why not a hydraulic lift of sorts... no electricity at all... and perhaps simpler?


      -Mark
       
    5. Pete

      Pete Well-Known Member

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      Thought about hydraulics, but the liquid reservoir would be heavy. Pneumatics is also an option I’m starting to look at, but assume this may be more expensive.

      [​IMG]

      This is the mast and boom in early development. I want an actuator / ball screw / Pneumatic system to push up the top section of the mast - this lifts and lowers the boom. There will be 200kg suspended from the end of the boom (see the arrow), which gives a moment at the mast of just over 8000N.

      I would like an "in-line" system because the motor etc of standard actuators is generally at a right angle to the rod of the actuator. This takes up a lot of room in the base of the hoist where I need to put some other bits and pieces while keeping the size to a minimum.
       
    6. mvalenti

      mvalenti Well-Known Member

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    7. Pete

      Pete Well-Known Member

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      Thanks Mark,

      I think 2 and 12 tonnes might be a bit of overkill, but oddly both designs are roughly the right size and shape for my needs. So will definetly investigate further!

      The original design that the company still use is based very largely one car equipment, and part of the brief is to make it more aestheticaly suitable for home use!
       
    8. mvalenti

      mvalenti Well-Known Member

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      Yes, they are over kill, just something to get creative juices flowing. Good Luck!

      -Mark
       
    9. kennovation

      kennovation Guest

      cool....nice design.. thanks for sharing.
       
    10. bpmufx

      bpmufx New Member

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      Hi there, this is my first posting. Nice to meet you all.

      To you question; yes for sure a custome linear actuator is possible and in my opinion, very
      appropriate for you application. Pneumatics and hydraulics systems are just that (Systems).
      There is a lot of other overhead required for those systems to work, And, then you must
      consider the ways they can fail. If they fail, is clean up an issue? Both practically and
      envoronmentally.
      So for these reasons Linear actuation has become the device of choice in most all robotics.
      from CNC Machines to entertainment robots.
      So as far as linear force required and motor torque is concerned, you are best served to contact
      the application Engineer from a suitable source of linear actuators. Not distribution channels like
      Harbour freight. While they sell various things they do not support any product.
      My favorite actuator mfgr is Motion systems Inc. I've done business with them for years, and they
      will help engineer your actuator. Once you know the lead screw size, figuring the torque is a two step
      process.
      1- how will you drive the lead screw? Belt? Gear? Direct coupler? etc.
      You will need this sorted out before you source a motor. and don't forget to decide if your system requires
      position sensing. This will be an added source of trouble if you don't plan it in early.
      2-choosing the motor is finally derived from determining the ratios built into the drive mechanism, and duty cycle
      of your system.
      Hope this helps.
       
    11. ismailagni

      ismailagni New Member

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