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stepper motor as clock drive — Parallax Forums

stepper motor as clock drive

zippyflounderzippyflounder Posts: 38
edited 2008-10-24 08:03 in General Discussion
I have been knashing my teeth over a high powerd clock drive, as the arms are huge and heavy. I was wondering what you all thought of using a stepper motor or contiunius rotation servo as a drive? How would we set it, could it be made to be accurate enough to keep time?

Comments

  • VelocitVelocit Posts: 119
    edited 2008-10-23 01:06
    I could certainly work, but you might need to use a simple geartrain to achieve the desired precision.

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    -Paul
  • zippyflounderzippyflounder Posts: 38
    edited 2008-10-23 01:11
    was wonding if you used 2 one for "hour" the other for min..
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-10-23 02:45
    I'd use a 12:1 geartrain between the hour and minute hands and drive just the minute hand. This can be driven through additional gearing to reduce the needed torque to a reasonable level. (The clock hands are counter-balanced, right?) You can add an absolute encoder to the hour hand, if you like. A 12-bit (4096 position) unit will give you better than ten-second accuracy.

    -Phil
  • zippyflounderzippyflounder Posts: 38
    edited 2008-10-23 02:47
    this is for small scale production so would like to stay away from gears.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-10-23 04:46
    Gears may be cheaper — even in the short run — than multiple high-torque steppers. If not gears, you could use timing belts or chain-and-sprocket arrangements.

    -Phil

    This isn't SX-related and probably ought to get moved to the Sandbox.
  • zippyflounderzippyflounder Posts: 38
    edited 2008-10-23 05:42
    was thinking of using the sx, might·be overkill though.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-10-23 13:57
    This thread is being moved from the SX Forum to the Sandbox Forum as it is off topic in the original forum.

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    Chris Savage
    Parallax Engineering
  • John BondJohn Bond Posts: 369
    edited 2008-10-24 08:03
    I’ve used stepper motors to make gauges, some them quite large, over 550mm in Diameter. They work well. These days, I use servos partly because the meters are smaller but mainly because servos are easier to interface. Servos are not suitable for clocks because they are not accurate but steppers work extremely well.
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    One point of caution, the step size of your motor must match the time resolution. For example a 100 step motor won’t work very well for seconds because each second needs 1.67 steps. 1st needle movement points to 1.2 secs, next is to 1.8 secs, then 3 secs and so on.
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    You need to know when the needle is at Zero (probably 12:00 in your case) so you can eliminate any slip that may have occurred. In my case, it was easy, I just drove the needle against the Zero pin but with a clock you would probably use a minute magnet on the needle and a hall effect sensor at 12:00 (or where-ever you decide).
    ·
    You can use 2 (or 3) steppers but as the shaft on one of the needle is a tube round the other shaft, you will probably need some sort of gear or belt drive anyway. Maybe you have some creative solution to this problem. If you do get one, please share it with us.
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    lol.gif·The most amusing part of a stepper clock like this is you can run it backwards and at different speeds. This really confuses people.
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    Kind Regards from the Dark and confusing continent – Africa
    John Bond

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