I need to construct a disk that rotates once over 24 hours (so a clock is 2 times too fast) What’s the best way to do this?
It would help to know what you need this disk for. For example how big does it have to be and does it have to support weight?
Take a disk that meets all of your other requirements, and position it at the north or south pole. Rotation problem solved!
If a clock motor has the size and power you need, just buy a 24-hour clock instead of the stupid 12 hour clocks commonly sold in the US: http://www.amazon.com/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3A24%20hour%20clock
Yes, some of those are 12-hour clocks with a dual dial showing both 0-11 & 12-23. But many have actual one-rev-per-24 hour faces & mechanisms.
There are also any number of mechanical timers, as used for lawn sprinklers, pool motors, etc. which are also 24 hours per revolution. One of those could be MacGuyvered into what you want.
A clock would work fine if the hour hand mechanism spun a gear that was adjacent to a gear twice as large. Put the disk on the bigger gear. The bigger gear rotates at half the speed of the smaller gear, thus one full rotation every 24 hours.
Specs?
Size, weight, reliability etc
Constraints?
Budget, your abilities.
Hour hand on an old synchronous motor clock run from a 25/30Hz source (requires some electronic chops) Edit - I see LSLGuy has the perfect clock.
Stepper motor driven by a microcontroller with stepper interface (some programming chops) Will drive a much bigger disk.
I’d look for something like a used 24 hr temperature chart recorder and gut it for the parts you need.
There are many for sale online. Amazon prices about 41-58 dollars. Search ~clock 24 hr face.
For five bucks and up, you could use a lamp timer. Those things run a 24-hour clock.
Believe most, if not all of those things spin their face clockwise.
A synchronous motor connected to an AC power outlet will rotate at a precisely controlled speed. You can get a geared synchronous motor, and add a few gears to lower the rotation down to 1 rotation per day.
Not quite. That would yield one rotation in 23:56:04.
Does the movement need to be continuous/smooth? Or can it be jerky?
That depends on what you’re counting the rotations against. For the OPs purposes the nitpick would have been that it yielded zero rotations. (Ignoring the movement of the ice sheets.)
The clock goes 2, or 24 or 24*3600 times too fast…
However if you add a belt drive system… eg you could be sure it was 2:1…
I think any device which contains added parts would have to incorporate some means of fine-tuning the speed to compensate for increased friction.
Wild guess: maybe the OP is planning to use this construction for astrophotographical purposes? Like, stick a camera onto the disk, point it at the celestial pole, and use a really long shutter speed? In which case Xema’s remark is of some relevance: what the OP really wants is a full revolution in one sidereal day.
Geez, I go to all of the trouble of typing ‘24-hour wall clock’ into Amazon, finding one, and copying the URL, and you had already beaten me by a day and a half!
@ignotus: If he wanted a camera drive for astrophotography those are readily available for not much money. With star finders, latitude compensation, and all the rest.
I wonder of the OP will ever grace us with his presence again so we can learn more about his mission and the rest of his requirements.
RTFT my friend. Read the *full *thread.
That’s saved me many minutes of helpful but too-late research. 