Since most of those cheapo movements are a simple single-coil motor, energized with alternating polarity short pulses, it would seem that there is no need for a "24 hour" movement. You can just have your micro pulse it twice the normal period, but with the same as normal pulse width(s). Check out the movement teardown in "lunchtime clock" at Instructables.com - http://www.instructables.com/id/Lunchtime-Clock/
Bob LaJeunesse >________________________________ > From: Jim Lux <[email protected]> >To: [email protected] >Sent: Monday, January 20, 2014 7:04 PM >Subject: Re: [time-nuts] 24 hr clock movements... > > >On 1/20/14 3:32 PM, Rex wrote: >> That listing is a bit vague about if it has a second hand. For the kind >> of pulse drive that has been discussed here, it seems you would want a >> definite second capability and step vs. smooth second hand drive. >> >> I know nothing except a little web searching, but this one seems to have >> the right features... >> http://www.clockparts.com/clock-part/24-hour-high-torque-movement/ >> >> but, although they mention a 24-hour dial available, the page for it on >> the site has no content. >> > >it is very much a matter of buying a few and trying them. > >If you don't install a second hand, then that solves the inertia of the >secondhand problem. > >The challenge is that because the "motor" for these things is basically a step >at a time, if the hand has too much inertia, then the hand will either not >move enough to get to the next tep (dying battery syndrome we've all seen), >or, it will move past (because the "braking torque" isn't high enough. > >It's sort of the torsional resonance effect that afflicts stepper motors in >another form. The magnetic impulse is basically driving a spring (the >magnetic field) with a mass on it. > >These things are always highly idiosyncratic. I would imagine that fiddling >with the duration and magnitude of the step pulses (or, for that matter the >"shape" of the pulse) could have a huge effect if one wanted to optimize it. A >couple decades ago we built a large (5-6 foot diameter) stopwatch prop with a >stepper motor, and we had to play with the drive voltage, the capacitance and >resistance in the step channels to make it work right. Today, you'd do >microstepping, or use a clever algorithm to customize the step waveform. >Generally you want a voltage profile that's sort of a spike (to get the >current flowing in the winding) with a back porch, and then a reverse polarity >at the end (to stop the motion). > >(I note that this problem is not unique to AA powered clocks. The hands of >the clock on the UC Berkeley Campanile are wood for a similar reason.) > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
