A motor that can slowly complete a rotation over 24 hours?

I'm trying to find the terminology used to describe the type of motor I'm looking for.

I want to power a clock-like device by a motor that would slowly and continuously spin one full rotation over a 24 hour period. It would not quickly spin around once a day at say, noon, and then wait until tomorrow to spin again.

As far as I can tell- this is a very big ask from a motor? I've tried googling and looking at the different types of motors, and all I can see is I think stepper motors would be a bad choice, but I don't know what a good choice is. Continuous rotation servo motors? Could they handle a task like this? Would this be a task for a high-end motor, or can I get a hobby motor to work?

I'm so sorry for such a newb question. Thank you in advance.

Are you sure you want a motor to turn that way or just an output shaft on perhaps a gear box?
Look no farther than a clock motor

Do you think a clock motor/gearbox could be made to run at half speed? Since they're made to rotate twice a day? If it can handle that, it would make my life so much easier.


I'll see myself out.

A stepping motor might be the thing to use.

Lets say a stepper has 2048 full steps per revolution, 28BYJ-48.

There are 86400 seconds in a day.

At 2048 steps per revolution, you need to step the stepper every 42.1875 seconds.

Pfffft. That would make the clock run backwards. :slight_smile:


My barber has a clock just like that!

Not enough information,

  1. How "strong" does the motor have to be?
  2. You suggest a stepper is not a right choice, can you tell us why.
  3. How accurate? Could a DC motor running a gear train be slowed by reducing the voltage (assumes you cannot find a 1/day motor)
  4. Power source? AC or DC
  1. Strong enough to push these gears plus heavy clock-hands plus whatever gearbox is needed to slow it down to one rotation per day.

  2. I thought a stepper was a bad choice because I was under the assumption that they would have very small numbers of steps per rotation. If LarryD is right that some have 2048 steps and I could step once per 42.1875 seconds, then that would be great.

  3. Accurate enough to keep time.

  4. DC. I'm using an Uno board for another section of the clock, and I want to use an adafruit motor shield, so only DC motors or steppers would work with that. I don't have to do this, but I'd like to.

With what accuracy? How many seconds a day for example?

Well the clock hands are only daily, monthly, and yearly. So not atomic clock accurate, but honestly if it's a minute off a day that does add up to 6 hours a year. That would be annoying, and I'd like to avoid it, but if it's the difference between a 20 dollar motor and a 200 dollar motor, I'll take it.

I just don't know a thing about motors.

Edit: If I need to- I bet I could add some sort of sensor to the clock to make it ping the internet at the Uno board's midnight, check the internet to make sure it really is midnight, check if the day-hand is over the midnight position, and if it's not- rotate the day hand until it reaches midnight. That's just a lot of complexity (and internet connectivity) that I hope isn't necessary.

You can buy quartz clock mechanisms that do this off the shelf, plus they keep excellent time.

I'm honestly thinking of doing this, I'd just have to buy a big huge sturdy one- and that's fine.

Not necessarily. It is normal practice to balance clock hands when they are heavy, so the torque requirements remain manageable. If they are so heavy that the sheer weight of the hands hanging on the shafts from the motor is a problem, then yes, you will need to buy something more robust.

Finally, do the hands have to be so heavy?

This mechanism would control 3 hands. 2 of them would be fairly light, but the third I don't think there's much a way around the weight.

I'm making a replica of the prague astronomical clock (for some reason, no one sells one that actually moves- they're all just normal clocks with this clock face.) I don't know if it's easy to make out- but there's three hands. Two of them are pretty normal, one has the little sun and the human hand on it, the other has the little moon. The 3rd is the big honker of the astronomical ring. It's actually a whole hand that ticks around.

Here I've color coded the hands so you can see. Even if I made it out of really lightweight board, that's a lot more stress than I think a normal clock hand can take.

Edit: This isn't actually how the real clock works either, the hand I've labeled "yearly" doesn't actually take a year to spin around, but instead is usually in step with the sun hand, but then once a day unlocks itself, goes a 1/365 step, and then continues to follow the sun hand.)

Nice project! You need to do some mechanical engineering, I would think, to offload some of the weight of that heavy hand from the movement. You could still balance it, though - it's usual to put the balance weight on the shaft, but behind the dial.

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