Bob said:
I have a project that requires turning a plastic disc (about the same size
as a CD) through 360 degrees in 7 days or 24 hours using a battery powered
system of some sort. The smaller and cheaper the better! Can anyone suggest
the best way I should approach this problem?
Thanks
Bob
Hi, Bob. The ideal solution for this would be a small AC gearmotor.
They're made for this kind of service, and they're inexpensive.
But if you need a battery-operated solution and the moment of inertia
of your disc isn't too great, an "easy button" relatively cheap
solution for one day rotation might be a 24-hour ham wall clock:
http://www.eham.net/reviews/detail/2794
It might be worth picking one up on ebay and just trying it. You only
need the clock movement -- the clock face itself isn't necessary. The
bigger clocks would probably have enough torque on the movement hour
hand to pull a CD-sized piece of plastic around with no problem, at
least while the battery was fresh. To get more torque, you may want to
wire up a "D"-sized battery to replace the AA. It would last longer,
too.
For a 7-day movement, some kind of gearing might be in order.
Another inexpensive solution which might give you more "oompfh" would
be to use a small 5V stepper motor, 3 or 4 "D" batteries or a 6V
lantern battery, and a PIC with some logic level FETs or darlington
transistors. It would be trivial to program in the long time delay
between steps. You could also use a switch to differentiate between
1-day and 7-day movement. The trick would be to pulse the stepper
coils for only a fraction of a second each time there's movement, like
the battery-operated clocks, to reduce long term power dissipation.
If you'd like to use a cheapie 4000-series CMOS and 555 solution to
replace the PIC, it would actually be quite a bit bigger and more
expensive, due to board space, number of ICs and construction hassles.
Also, a PIC with a ceramic resonator (+/- 0.5%) would be more accurate
and stable than the R-C oscillator of a 555 or CD4060 with a tweaker
pot. If you needed even more accuracy, you could use a crystal for the
PIC.
If you're looking for that type of solution, or if this isn't enough,
you should post again with more detail on your project requirements.
Good luck
Chris