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.

Searching eBay gave some hits, but most of what I saw for 24-hour
movements seemed to have smooth second hand (not step).

On 1/20/2014 10:17 AM, Jim Lux wrote:

On 1/20/14 3:32 PM, Rex wrote:

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.)

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

Jim, I think you missed the main point I was trying to address.

It seems that many of the newer quartz movements do not move the second
hand in one-second steps. They move it in some way that appears smooth
to a human observer. (Even if there is no actual second hand, the same
motive issues need to be looked at.) I assume the smooth motor is still
some kind of stepper but being driven by pulses at a much higher rate
than a one-second rate. If you receive one of these versions, you will
have a more difficult job to drive it. You'd need to figure out what
rate is driving it and generate that. The 1-second step versions would
be easier for us to generically interface with.

The description on the Klockit page wasn't very clear about which type
it is (also it was somewhat ambiguous about using a secondhand, at all,
if desired -- there is a footnote that I couldn't quite decipher).

On 1/20/2014 4:04 PM, Jim Lux wrote:

I think there is a slight flaw in slowing the drive to half rate. The
hour hand could then go around once in 24 hours, but the minute and
second hand movement is halved too. Rather non-intuitive to read unless
you only put on the hour hand and make a new 24-hour dial face.

On 1/20/2014 5:57 PM, Robert LaJeunesse wrote:

On 1/20/14 5:57 PM, Robert LaJeunesse wrote:

The difference is that a 24 hr clock has a 24:1 gear ratio between
minute and hour hands, and a 12 hr clock has 12:1.

If you're doing hour hand only, yep, any movement will do.