Turntable controller: finalised project proposed

Erik84750 Feb 12, 2024

  1. Erik84750

    Erik84750 TrainBoard Member

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    When looking for a turntable solution for my layout I found a few commercial sites, such as this one. However the customer comments I read were not satisfying, and the response from the provider even less so.

    One of the most common comments was that the indexing system does not work well; creep in the course of usage resulted in tracks not being alligned properly anymore after hours of operation. The comments from the provider were not reassuring: he blamed that the creep was the result of the wooden support frames crimp and expansion due to moisture or whatever.

    So one of the foremost goals in this project is to have flawless indexing, and total-zero creep over the course of usage. For that matter I developed an algorithm that, during calibration, measures the exact amount of stepper moter steps to perform an exact 360° 0' 0" 0.1" etc.. turn.

    Several other requirements were set as goals prior to starting the actual development.

    One of the peculiar and most important hardware parts (besides the stepper motor) is the indexing sensor.
    Some other projects use a Hall effect sensor: this sensor uses the magnetic field of an external object to sense its presence.
    There is however a very big disadvantage to this sensor.
    Since magnetic fields do not have clear on/off boundaries it is virtually impossible to get a magnetic object to approach within a specific distance where the sensor will detect its presence and expect that distance to be over and again to be identical within millimeters, or for the requirement of turntable operation, within tenths of millimeters.
    The decision to use in this project a specific optical detector, with a narrow and highly selective field of view, was taken after hours of testing of its repeatability and repetitivity (statistical terms describing the accuracy of measurements). This detector is described further along with all the other specifics of this project in this Github page.
     
    Last edited: Feb 12, 2024
  2. Bob Brockhouse

    Bob Brockhouse New Member

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    Great project Erik. Have been waiting for an accurate DIY turntable controller after playing with other
    designs which were disappointing in repeatability of accurate positioning.
    Would like to ask if you are using the HC-020K sensor with the slotted disks that usually come with
    the sensor, one having far more slots than the other. I refer to what I see on Ebay. The sensor is
    available as a sensor only or with disks. Thanks.
     
  3. Erik84750

    Erik84750 TrainBoard Member

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    Hi Bob, thank you for your kind words.
    The sensor is indeed the HC-020K; no slotted disks required.
    The turntable disk should be equipped with just one small protruding object that passes through the sensor "eye", mounted underneath the framework, out of sight. This object may even be the size of a nail; as long as it passes through the sensor lips.
    The purpose being that this object passes through the sensor eye once every 360 degree rotation of the turntable.
    I updated the github description just now to reflect this clarification.
     
  4. Bob Brockhouse

    Bob Brockhouse New Member

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    Hi Erik, My build is progressing albeit a breadboard bird's nest at this stage. Awaiting the slow boat to
    deliver the sensor. Meantime, have the LCD, encoder and keypad responding as seen from your Github photo's.
    At this point must ask which version of Accelstepper.h should I be using ? My library is currently set at
    version 1.64 most recent apparently. As presented on Github, does the INO file need to have some
    commented lines uncommented to use a NEM17 stepper ? I dare to assume by default the INO is
    currently compiled for the smaller 28BYJ stepper ?

    Apologies for the questions, just not as experienced as others but try to keep the brain cells ticking.

    Thanks again - Bob
     

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