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Thread: mechanical timer

  1. #1
    Associate Engineer
    Join Date
    Oct 2012
    Posts
    1

    mechanical timer

    Hi, I am trying to design a mechanical timer that initially opens and then, when the time runs out, shuts a lever (90 degrees). The open and shut process can not be too gradual; it can take max. one or two minutes out of a total 60.
    My initial idea was to put a gear on the main axle with only a few teeth so that it will turn another gear attached to the lever during the first and last 2 minutes. (Appropriate sizing of the gears would enable this. e.g. 12 degrees on the first gear to turn 90 on the second.)

    The lever requires torque of 0.5nm. How do I work out the torque of a gear to see if it provides enough force?

    What is the best way to increase torque (if necessary) in such a situation?

    Does anyone have a better idea how I could open and shut a 90 degree lever with a mechanical timer?

    (the lever is on a ball valve)

    Thanks

  2. #2
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Hi and welcome.

    Your suggestion of the gear with a few teeth is fraught with great risk of failure. The gears may not mesh exactly when called upon. They may not close or open the valve fully unless you are stalling the motor at each end of travel.

    Ball valves have quite a high level of operational stiffness. You would want to know that before calculating required torque.

    Increasing torque? Change the diameter of the gears.

    What drives the driving gear? Is it an electric motor or what? Can you use a stepper motor there and go with full-teeth gears?

    From the little you have described, this does not sound a like a good reliable approach to the design.

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