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Computer aided Rotating platform

  1. Jul 21, 2016 #1
    I'm thinking about building a rotating platform (horizontal rotation, like merry-go-round) which will be controlled by computer instructions. the platform will rotate with accuracy to 1 decimal point degree. a load will be mounted on this rotating platform, could weigh up to 200kg. what's the best mechanism for this? pneumatic? magnetic? thanks
     
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  3. Jul 21, 2016 #2

    Mech_Engineer

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    When you say "controlled by computer instructions" what method of motion control are you planning to use exactly? Stepper motor? Servo w/ encoder? Direct Drive?

    Have you considered purchasing an off-the-shelf solution such as this one?

    Aerotech AGR Mechanical-Bearing Gear-Drive Rotary Stages
    upload_2016-7-21_8-4-36.png
     
  4. Jul 21, 2016 #3
    so, what I'm planning to do is mounting a heavy duty telescope on this platform. after calculating certain star's position, I will input that coordinate, and based on the current platform position, the platform may need to be rotated n degrees (1 decimal point accuracy, so something like 2.7 degrees counter clockwise, etc)
    which mechanism will get the precision I need, but enough strength to rotate the load (with minimum power)?
    perhaps like this one

    it's using air bearing, so reduces wear and tear (no friction at all) significantly? but this looks kinda costly.
    Cost is a main concern. I'm willing to build my own mechanism. any hints? I'm a software programmer, no background in mechanical engineering.
    thanks
     
    Last edited: Jul 21, 2016
  5. Jul 21, 2016 #4

    Mech_Engineer

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    Star tracking is a pretty complicated problem, have you considered that you will need adjustments for both azimuth and elevation?
     
  6. Jul 21, 2016 #5
    yes, this rotating platform is for the azimuth. as for the elevation, I'm assuming that this will be another rotating mechanism, but it will be different (vertical like a ferris wheel and must also take gravity into account, unlike horizontal rotation which can ignore gravity altogether). Thanks
     
  7. Jul 21, 2016 #6

    Mech_Engineer

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    Sounds like you're on the right track. You essentially have two paths available to you:
    1. Buy a pair off-the-shelf rotation stages like the Aerotech AGR I linked (potentially an expensive option with the control hardware)
    2. Design your own rotation mechanism using bearings, gears and mechanical know-how, and then implement a drive motor of your choice and sufficient for your torque requirements.
    Option (1) gives you the potentially most robust path (especially if the telescope is indeed heavy as you claim) but will cost a good amount of money (potentially tens of thousands).

    Option (2) is possibly cheaper if you can put in the engineering time yourself, but not guaranteed to save money when considering the cost of fabricated parts and hardware.

    So, is this a personal project or a professional one? Do you have a budget and/or timeline in mind?
     
  8. Jul 21, 2016 #7

    Mech_Engineer

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  9. Jul 22, 2016 #8
    this is a personal project. me and some of my astronomy enthusiast friends are thinking about recording the movement of some stars for starters. and yes, this is a huge telescope with other equipments also mounted on it. we never really measure the actual weight, but a guesstimate is around 200kg.
    what motion control method do you recommend? what are my options? My priorities are:
    1. precision (1 decimal point degree)
    2. minimum wear and tear (minimum friction between the working parts)
    3. reliability (minimum effort to recalibrate)
    4. power consumption
    turning speed is not a problem. 1 degree per second is fine, so something like lazy susan is ok
    if possible, I'd like the budget to be less than $1500 (just for the platform)
     
    Last edited: Jul 22, 2016
  10. Jul 22, 2016 #9

    Mech_Engineer

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    Yikes, the weight of your telescope will severely limit your options. I think your best bet will be to design a more traditional altitude-azimuth gimbal mount, and then come up with a plan for motorizing it. See here: https://en.wikipedia.org/wiki/Altazimuth_mount

    This kind of design is mechanically simple, which could be good for your budget concerns. But, note that for tracking purposes this kind of mount has some disadvantages, specifically because it is not tilted to match the earth's rotation, tracking has to be done using synchronized motion in two axes with complex tracking algorithms to try and produce smooth synchronized motion.

    You should also take another look at your angular resolution requirement. Astronomical telescope trackers typically have angular resolutions measured in arc-seconds, which is 3,600 times the resolution you're proposing.

    https://en.wikipedia.org/wiki/Minute_and_second_of_arc
     
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