is there any advantage of central rotor over micro-rotor automatics?
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Thread: is there any advantage of central rotor over micro-rotor automatics?

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  1. #1
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    is there any advantage of central rotor over micro-rotor automatics?

    I wonder why there are no micro-rotor movements produced in large numbers given that is more beautiful and slimmer than the central rotor autos. The central rotor offers larger moment of inertia (to get the same inertia on a micro-rotor perhaps you need a heavy material as gold or tungsten). But in these days of tight tolerances and highly efficient systems, I assume even with less inertia, the micro-rotor can be effective. So I wonder what other advantages the central rotor has over the micro-rotor.

    Affordable Micro-rotors:




    high end micro-rotors:


  2. #2
    Member mleok's Avatar
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    Re: is there any advantage of central rotor over micro-rotor automatics?

    One obvious thing which comes to mind is that the balance wheel is typically extremely small on microrotor movements, so that might have an effect on accuracy?

    https://forums.watchuseek.com/f2/does...ng-456423.html
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  3. #3
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    Re: is there any advantage of central rotor over micro-rotor automatics?

    The balance wheel is definitely an interesting factor when playing with size like this. Theoretically, this can always be mitigated just by using a larger diameter movement itself and thus creating space for whatever balance you want. There are some other tricks, which most or all free-sprung balance makers are using, like Patek's Gyromax above moves the collets to the top of the balance to lower the effective diameter of the balance, and Rolex's Microstella moves the screws on the inside of the balance...this is opposed to many older systems which had the screws on the outside, increasing the effective diameter of the balance. Additionally, small balance wheels are often used in high BPH movements, where large balance wheels are generally used in low BPH movements, perhaps implying (with no certainty, mind you) that upping the BPH might take advantage of the small balance and give a return on accuracy and precision.

    I think, more obviously, the super efficient winding systems and ultra-heavy rotors are not simply available to microrotor systems, they can and are being implemented in the ordinary automatic winding systems already. Thus, in a head to head matchup of winding efficiency using similar designs and materials (obviously one being a micro rotor and the other being conventional), I think the centrally mounted one will basically always win.

    Now, to the degree more "efficient" automatic winding matters is a whole other discussion...if the microrotor can easily keep the watch fully wound when wearing it, the only improvement you'd get out of a comparable ordinary system is that it would achieve full wind faster...which, while advantageous, is not that big of a deal.

    Some companies try (and perhaps do) have it both ways...



    Whether or not this actually does allow the watch to be thinner (the GO version, that is) I can't say.

    It's an interesting topic.

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    Member Bergarn's Avatar
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    is there any advantage of central rotor over micro-rotor automatics?

    What kind of power reserve does a micro rotor movement lend itself to?

    I assumed that a smaller rotor wouldn't have the same momentum and you therefore have to/would use a weaker mainspring. Obviously you could then gear the winding mechanism accordingly to extract enough power from the rotor (like CitizenM said about winding it full, just takes longer), but you must reach a point where it's just not practical and there would have to be too many rotations to wind the watch and it would never actually fully wind.

    So my theory is winding, and the less headroom of winding power doesn't lend itself to play a lot with the other power-hungry features of the watch.

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    Re: is there any advantage of central rotor over micro-rotor automatics?

    Quote Originally Posted by CitizenM View Post

    Now, to the degree more "efficient" automatic winding matters is a whole other discussion...if the microrotor can easily keep the watch fully wound when wearing it, the only improvement you'd get out of a comparable ordinary system is that it would achieve full wind faster...which, while advantageous, is not that big of a deal.

    Some companies try (and perhaps do) have it both ways...



    Whether or not this actually does allow the watch to be thinner (the GO version, that is) I can't say.

    It's an interesting topic.
    This is exactly my point, if the advantage of better inertia is not significant, for aesthetic reasons I would prefer a micro-rotor to a central rotor auto.

    BTW, the GO looks nice, but even nicer would be if they could put the balance wheel above the rotor - a design similar with old pocket watches could be possible - here is a modern interpretation (non-auto though):

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    Re: is there any advantage of central rotor over micro-rotor automatics?

    Quote Originally Posted by Bergarn View Post
    I assumed that a smaller rotor wouldn't have the same momentum and you therefore have to/would use a weaker mainspring.
    This is correct. But the solution is quite simple (at least in high end watches): use a heavy metal (gold) for the rotor (on a cheap watch this could be replaced by tungsten). The gold (or tungsten) density more than doubles steel's density so it partially compensates for the half radius of the rotor.

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