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    Discussion in 'The main mechanical design forum' started by Camaro51, Jan 25, 2013.

    1. Dana

      Dana Well-Known Member

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      The first step in any kind of design is to clearly define the problem. Some questions would be:


      • How fast does it need to move up and down?
      • How rigidly does it need to be supported when up (against rocking of the boat, pushing buttons on the device, etc.)?
      • Do you need a fail-safe to get it up or down if the mechanism fails?
      • What about water intrusion and its effect on the components? Corrosion is likely to be a problem, especially if you're on salt water.
      • Is there room for mechanism below, or on the sides, or both?
      • Is there a magnetic compass nearby (could be affected by electromagnetic fields of the motors, or steel components)?
      • Have other people done this before? If so, how? If not, why not?

      Next, break down the mechanism into separate functions:


      • Linear guiding
      • Driving up and down
      • End stops

      Once you have clearly defined the problem, the solution often becomes obvious.

      The suggestion of a car window actuator and gas springs (gas spring to lift it slowly, perhaps a small motor winch to pull it down) are good ones. A scissors mechanism is good when you need it to be very compact when collapsed, but linear bearings alongside or below, while less compact, are much more rigid and smoother operating.
       
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    3. Dave B

      Dave B Active Member

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      Re-Use

      I like Dana's last comment to look at existing devices for inspiration.
      An old VCR tape deck has a motor and caddy with gear train moving a rack in and out.
      His car window mechanism or a electric seat mechanism are excellent ideas to get you started.

      I often tear down items from a store to begin a test bed utilizing aspects of the device to get started.

      You mentioned you were not very mechanically inclined and the problem you were wanting to solve was a 1 up device for you boat.
      The discussion of how to limit the forces to lift the box using springs is desirable. weights on cables is not since the motion on a boat is unpredictable causing weights and cables to derail etc.

      Dave
       

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