Tiny motors for a computer-controlled analog watch

Discussion in 'The Projects Forum' started by sambooch, Aug 5, 2014.

  1. sambooch

    Thread Starter New Member

    Aug 5, 2014
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    Hey there,

    I'm doing research into a project that I've been looking to get off the ground. I'm trying to make an analog watch, in the sense that it will have physical hands, but I want the hands to be controlled by a microprocessor. This way, a time can be entered and the hands will instantly jump to that time, and the watch can set itself via wifi. I would probably only include an hour hand and a minute hand.

    My question for all of you is about the motor(s) I should use. They have to be small enough to fit into a wristwatch, so I was looking into pager motors. Can these be programmed to move at 1 minute and 1 hour intervals? And if all I can get my hands on are the weighted motors used for vibrations, will these function normally without noticeable vibration at low speeds, and will they provide the precision that I need?

    Thanks!
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Fit into a wristwatch? That will be a very challenging project from a mechanical perspective.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Motor Electronic Goldmine, # G19962, L-10mm, D-4mm, shaft 2mm X .71mm, 1.1-6V, 10,000RPM, 85mA, 13 Ω, $ 1.79.
    With attached absolute encoder you could make it go where ever you wanted, finding one to match motor - unknown.
    Task-for me= impossible.
     
  4. mcgyvr

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    Oct 15, 2009
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  5. sambooch

    Thread Starter New Member

    Aug 5, 2014
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    Yeah, it's going to be tricky, which is why I want to make sure it's even possible before I try to tackle it.

    Thanks Bernard, that looks perfect. What about it makes it impossible?

    Awesome, mcgyvr, I'll start doing my research.
     
  6. Bernard

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    Not impossible, just not possible for me. The squiggle looks promising.
     
    Last edited: Aug 6, 2014
  7. sambooch

    Thread Starter New Member

    Aug 5, 2014
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    From the research I've done so far, it looks fairly simple to get a small enough motor. The real trouble is trying to find a small enough encoder.
     
  8. RichardO

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  9. THE_RB

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    You don't need encoders. Just use a tiny 2 phase motor and drive it at the correct frequency.

    Or even the correct design of one phase motor, like they use in cheap household dial clocks.
     
  10. sambooch

    Thread Starter New Member

    Aug 5, 2014
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    Yeah, using a display would be far easier, but this is more of an experiment that I want to try since I've never seen anything like it. I know it sounds like I'm over-complicating things, but I guess it's almost a challenge.

    I was considering using AC motors, but I can't find one small enough. They don't seem to make them as small as DC motors, at least not for cheap. As for the one phase motors, do you mean stepper motors? Can they quickly turn to a specific angle in a fraction of a second?
     
  11. RichardO

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    Right now I am wearing a Casio AQ-102 which has hour and minute hands. This watch sets the time using push buttons -- there is no setting stem. The minute and hour hands are are geared like a conventional watch; they are not moved separately. If I remember right, it takes something like one or two seconds to move the hands one hour.

    For research, I would go to Wal-mart and buy the cheapest and biggest quartz movement analog watch that they have (less than $10 !). Take the back off and look at the motor and gearing. This will give you the scale of things that you have to work with.

    If you are daring you can try to drive the motor with your own circuit. Be warned that the wires are really, really small. The watch I tried this on did not survive.
     
  12. sambooch

    Thread Starter New Member

    Aug 5, 2014
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    Oh wow, I looked at some videos of the AQ-102. That's the closest I've seen to what I'm trying to do. I'd love to tear one of those open.

    I'm looking for a motor that can make that time switch instantly, though, and it doesn't look like those traditional watch motors are capable of that.

    I'm now considering using a pager motor with an integrated circuit magnetic encoder, like this one:
    This seems like it would still work with a tiny pager motor as long as it has a proper mount, but I haven't been able to get in contact with the manufacturer to confirm. Am I wrong about this?
     
  13. RichardO

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    May 4, 2013
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    Some thoughts:

    You can use two motors, one for the hours and one for the minutes. That way even the slow watch motors will set the time in less then a couple of seconds. That would be plenty fast enough for me.

    Keep in mind that a watch normally uses a very small battery and has to run for a year or more. The slow stepping motors, like used in watches, use little power. DC motors, like pager motors, run fast and draw a lot of power, in comparison.

    If you use a stepping motor then you do not need to know the current position of the hands. You only need to know when the hands at a known position such as 12 o'clock. When you install the battery, the hands are moved to the known position and then the clock circuit uses the number of steps applied to the motor to know where the hands have been moved to.

    One way to learn about what works best is to build a larger version such as a wall clock. The size, mechanics and power requirements won't be as big an issue.

    I believe battery powered wall clocks use a stepper motor. I think I would try converting a battery powered wall clock module like you can get at hobby stores. It might take two modules -- one for the hours and one for the minutes.
     
  14. THE_RB

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    Feb 11, 2008
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    I second that. Cut your teeth on a wall clock and get the concept and driving electronics sorted.

    Then see if you still want to make a watch! ;)
     
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