Feedback from a motor for an analog clock or watch

Thread Starter

4096

Joined Nov 6, 2020
12
I am planning to build analog clocks and watches. I've considered using a stepper motor or servo motor to run the gear train so the motor can rotate the correct amount. However, I can't find small enough stepper motors and servo motors. I can find small enough DC motors. I have considered putting a plastic ring around the shaft of the DC motor with a few pieces of metal in the ring so that when the metal pieces move to the right position, a circuit would be completed which would send a signal to a microcontroller. The microcontroller would send voltage to the motor to make it move. When it gets the signal from the completed circuit, it would stop sending the voltage until the next second begins. However, someone told me he thinks that with my plan, since the metal pieces would rub against each other every second, that they would wear out and no longer make contact. I have also thought about using a limit switch, but they say they have a lifetime of 500000 (which I assume is the number of times the switch is clicked). Since the limit switch would be pushed once per second, it would reach 500000 clicks after 5 or 6 days.

Does anyone think my plan for a completion of a circuit would work? Would limit switches likely last longer than 500000 clicks? Does anyone know where I can find small enough stepper motors or servo motors to fit inside a watch?
 

Ya’akov

Joined Jan 27, 2019
6,556
What size do the motors have to be? It is hard to make a recommendation without knowing what you need.

These are pretty small, and there are smaller ones too.

1646000794650.png

For your scheme, which I am not sure is workable, I would start with the idea of using magnets and a hall effect sensor. This is usual way to index positions on small motors. You might also be able to use an inductive sensor like the crankshaft position sensor in a car engine. But I don't think there are any small enough.
 

MisterBill2

Joined Jan 23, 2018
13,123
Using a DC motor and a speed control is not a reasonable approach if the clock needs to be accurate. And small stepper motors certainly are available, but evidently not where you have been looking.
But a small DC motor without speed control, that will advance the clock one minute, with an indexer mechanism, each time it runs, could easily work. Then just a simple counter to run it once per minute.
 

MrSalts

Joined Apr 2, 2020
2,353
Use a small solenoid and ratchet mechanism like most quarts clocks move the second hand. Go to a second-hand store, garage sale or Goodwill and buy a few electric clocks. You'll not find a stepper motor. You'll find a coil, a spring and a ratchet mechanism. You'll find two AA batteries (3v total, a circuitboard with a 32.768kHz crystal, blob of black epoxy (a cd4060 chip is under there), a flipflop, a small transistor and a coil on a small piece of silicon-steel with a spring. Tick, tick, tick.
Take apart a few battery operated clocks for reference.
 

AlbertHall

Joined Jun 4, 2014
12,157
Use a small solenoid and ratchet mechanism like most quarts clocks move the second hand. Go to a second-hand store, garage sale or Goodwill and buy a few electric clocks. You'll not find a stepper motor. You'll find a coil, a spring and a ratchet mechanism. You'll find two AA batteries (3v total, a circuitboard with a 32.768kHz crystal, blob of black epoxy (a cd4060 chip is under there), a flipflop, a small transistor and a coil on a small piece of silicon-steel with a spring. Tick, tick, tick.
Take apart a few battery operated clocks for reference.
The battery clocks I have taken apart have no ratchet.
For instance: https://www.instructables.com/whats-in-a-quartz-clock/
 

MisterBill2

Joined Jan 23, 2018
13,123
The battery clocks I have taken apart have no ratchet.
For instance: https://www.instructables.com/whats-in-a-quartz-clock/
For a limited time, battery wall clocks were made similar to the mechanical car cocks, and did have a mechanism that used a ratchet. That was many years ago, in the earlier 1960's time frame, in the USA. I have no ideas as to how the rest of the world did it back then. The electronic stepper motor ones came later, in the 1970's era. Also the mechanical digital clocks.
 

Thread Starter

4096

Joined Nov 6, 2020
12
Thanks for the responses. I think I'd like to try a solenoid and ratchet approach. I've been looking at amazon.com for parts. I'd want the solenoid to be no more than 10mm long, including armature, and no more than 5mm wide. The smallest I could find on amazon.com are 30mm long, not including the armature. A problem when searching for ratchet gears is that since ratchet also refers to socket wrenches, so the search results on amazon.com for ratchet gears turns up results for socket wrenches.

I looked on Digikey and the smallest solenoid I could find is 13.2mm long and 9.6mm wide. Also, when I look at an entry on digikey.com there is an entry called "Standard Package". Is this the number of pieces included in each package? This one https://www.digikey.com/en/products/detail/delta-electronics/DSTL-0216-09/5213971 has a standard package of 324 and is $13.94 each. I've seen entries around the same price but the standard package is only 1. $13.94 is far more than I'd want to spend per solenoid. I have the same problem on digikey.com as amazon.com when searching for ratchet gears I get socket wrenches as the result. However, maybe digikey.com only sells electronic pieces so a gear would have to be purchased elsewhere.

Does anyone know where I can buy smaller electronic parts and gears other than amazon.com or digikey.com?
 

MisterBill2

Joined Jan 23, 2018
13,123
It is likely that for parts that small you will need to contact the manufacturers rather than distributors. and use different keywords.
also, you are more likely to find a small stepper motor than a small solenoid.
 

Ya’akov

Joined Jan 27, 2019
6,556
Thanks for the responses. I think I'd like to try a solenoid and ratchet approach. I've been looking at amazon.com for parts. I'd want the solenoid to be no more than 10mm long, including armature, and no more than 5mm wide. The smallest I could find on amazon.com are 30mm long, not including the armature. A problem when searching for ratchet gears is that since ratchet also refers to socket wrenches, so the search results on amazon.com for ratchet gears turns up results for socket wrenches.

I looked on Digikey and the smallest solenoid I could find is 13.2mm long and 9.6mm wide. Also, when I look at an entry on digikey.com there is an entry called "Standard Package". Is this the number of pieces included in each package? This one https://www.digikey.com/en/products/detail/delta-electronics/DSTL-0216-09/5213971 has a standard package of 324 and is $13.94 each. I've seen entries around the same price but the standard package is only 1. $13.94 is far more than I'd want to spend per solenoid. I have the same problem on digikey.com as amazon.com when searching for ratchet gears I get socket wrenches as the result. However, maybe digikey.com only sells electronic pieces so a gear would have to be purchased elsewhere.

Does anyone know where I can buy smaller electronic parts and gears other than amazon.com or digikey.com?
Apologies if you know what I write below, I am not assuming you don’t. If not, I hope it helps.

You are searching for the wrong thing. Clocks don’t have “gears” they have wheels. A search for ratchet wheels is much more fruitful. For example, this company selling clock parts.

But for a clock you need an escapement of which ratchet wheel can be a part but isn't nearly a solution. Escapements for clocks take other forms too but they all have something in common and that is gear reduction. You don‘t just need a ratchet wheel, you need a ratchet wheel and gear reduction that lets you get second wide movements, and it won‘t be one pulse it will take as many as the reduction requires to move to the next second mark.

You could use a 60-tooth ratchet wheel, but it is unlikely you will just happen to find one. As you can see common wheels run about 12 or so teeth. Perhaps you could have a special wheel laser cut if you design it as part of the mechanism. In any case, that ratchet wheel needs to be fitted into the escapement with a cam of some sort. The solenoid could be part of that. You can find some ideas with a search for “solenoid escapement”.

In any case, the mechanism is not simple, and you also have to deal with minutes and hours.
 

boostbuck

Joined Oct 5, 2017
239
THE Roman Black had interesting ideas for running very slow but accurate motor drives suitable for clocks. This is his page describing how, using motors with an optical feedback encoder on the shaft - such as the motors found in old VCR players.
 

Thread Starter

4096

Joined Nov 6, 2020
12
Yes, I know that an analog clock requires a gear train. I have worked out the following gear ratios (while considering using a stepper motor to drive the train):

second 24:8 30:12 = 7.5
minute 40:9 30:8 36:10 = 60
hour 24:8 36:9 = 12

This is based on an assumption that the stepper motor would rotate 1/8 of a cycle per second, so dividing by 7.5 would create a 1/60 rotation. Some of the stepper motors I have rotate in incrememnts of 1/2048 of a cycle, so I could not rotate it precisely 1/60.

I got the stepper motors that Yaakov suggested. However, I don't know how to connect the smaller stepper motors to power and ground, and I cannot find a data sheet. I have not done any soldering.

I also don't know how to drive stepper motors. I think I've read somewhere that at least some stepper motors work with four inputs, where to make it turn the steps are to first send current though only the first input, then both first and second, then just second, then second and third, then just third, then third and fourth, then just fourth, and finally first and fourth. However, I found this page https://forum.digikey.com/t/how-to-drive-a-stepper-motor/13412 that describes something that at least looks to me as entirely different. It also says not to put two transistors on the same time or it will short the circuit. I don't know which ones are on the same side.

Also, the small stepper motors I have appear to have four connections. The link I gave says a stepper motor has four wires and two coils. I don't know if the four connections are for the four wires or how to access the two coils. Also, it seems like a motor should have both a power and a ground connection but I can't figure out which connection is which.
 

jrb_sland

Joined Dec 24, 2021
9
I am planning to build analog clocks and watches. I've considered using a stepper motor or servo motor to run the gear train so the motor can rotate the correct amount. However, I can't find small enough stepper motors and servo motors. I can find small enough DC motors. I have considered putting a plastic ring around the shaft of the DC motor with a few pieces of metal in the ring so that when the metal pieces move to the right position, a circuit would be completed which would send a signal to a microcontroller. The microcontroller would send voltage to the motor to make it move. When it gets the signal from the completed circuit, it would stop sending the voltage until the next second begins. However, someone told me he thinks that with my plan, since the metal pieces would rub against each other every second, that they would wear out and no longer make contact. I have also thought about using a limit switch, but they say they have a lifetime of 500000 (which I assume is the number of times the switch is clicked). Since the limit switch would be pushed once per second, it would reach 500000 clicks after 5 or 6 days.

Does anyone think my plan for a completion of a circuit would work? Would limit switches likely last longer than 500000 clicks? Does anyone know where I can find small enough stepper motors or servo motors to fit inside a watch?
I don't want to be a wet blanket, but why build what you can buy? There are innumerable quasi-analog clocks & watches already in the marketplace. Most clocks run for about a year on a single AA alkaline cell, and keep time to a few minutes per year. John Harrison would have sold his grandmother into white slavery for this technology. {Google him}. Ditto for wrist-watches running on a tiny lithium coin cell. Given that you'll likely want to reset them twice a year to deal with Standard vs Daylight time, this is often adequate for casual timekeeping.
I'd like more information about your motivation. Do you want more precise timekeeping, i.e. a dial-faced clock synchronized to GPS time? I built a digital-display clock in 1985 that adjusted itself +/- 15 ms to WWV(H) time {look up WWV} but now gets its sync from a 2002-vintage Garmin OEM GPS receiver model 15L.
See https://www8.garmin.com/specs/GPS15HLSpec.pdf
You'll also need an antenna. See for instance: https://www.garmin.com/en-US/c/marine/boat-sensors-antennas/
GPS 1pps signals are easily good to better than +/- 1 us or thereabouts. Fancier receivers can deliver +/- 50 ns at a much higher price if you have a need for same. I'm now a lazy old man, but I've often thought about simply patching the 1 pps signal from a GPS receiver into the once-per-second guts of a cheap analog-dial clock to have low-maintenance millisecond accurate time on my shop/office wall. I repeat - what is your motivation?
BTW, there is lots of information on the web about stepper motors in their various versions. My advice is to download & study data sheets & user guides & tutorials easily available on manufacturers' websites. There is no substitute, imho, for carefully reading the literature before casually embarking on a fuzzy scheme. I'm not trying to be rude, just realistic. Grandpa Google {or DuckDuckGo} is your friend...
 

MisterBill2

Joined Jan 23, 2018
13,123
OK, the steppers have four wires, two for each coil. The drive scheme is a bit more complex, in that at least on the steppers that I am familiar with, there are polarity reversals going on as well. The driver circuit that you found is describing cautions required with what is called an "H-Bridge" , in that it has four transistors arranged in a pattern similar to an "H", with the coil being the crossbar portion. the coi is powered by switching on the top of one side and the bottom of the opposite side. This makes wiring a bit simper than for the six-wire steppers, but it adds to the complexity of the driver. It does reduce the cost of the motor windings a bit, though.
There are a number of sequences available for driving a stepper motor, the two original modes were half-step and full step.
I wil eave the explanations of the stepping to Yaakov, who is quite good at that.
 
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Thread Starter

4096

Joined Nov 6, 2020
12
I don't want to be a wet blanket, but why build what you can buy?
I wanted to avoid mentioning this so people would not tell me how unrealistic it is, but I am interested in selling clocks and watches. I'm also interested in implementing features like a perpetual calendar, as well as other features not available on clocks and watches on the market.
 

MisterBill2

Joined Jan 23, 2018
13,123
Besides making interesting hand-made clocks to sell, ANYBODY can buy an ordinary clock that is exactly like ten thousand other clocks.
The much more complex and totally one-off creations are much more than a utility item for seeing what time it is. I fully appreciate that somebody wants to create a different sort of clock.
 

MrSalts

Joined Apr 2, 2020
2,353
I don't want to be a wet blanket, but why build what you can buy?
I don't want to be an a-hole but why do I spend three days preparing and a day smoking a brisket when I can go out and by a brisket sandwich at a well-reviewed vendor? Because it is fun, challenging, rewarding, relaxing, gets me out of my wife's way, gives my wife something to complain about, something to spend my money on to keep the economy rolling.

What's the point of any hobby?
 

jrb_sland

Joined Dec 24, 2021
9
I wanted to avoid mentioning this so people would not tell me how unrealistic it is, but I am interested in selling clocks and watches. I'm also interested in implementing features like a perpetual calendar, as well as other features not available on clocks and watches on the market.
Again, please understand that I am attempting to assist you, but your language is imprecise. You say "I am interested in selling clocks and watches" but you have said previously you want to design & build your own. There is a GINORMOUS difference between the two statements. Please do your homework. Consumer-grade clocks & watches are "industrial rice", and unless you manufacture them by the 100s of thousands, you can't make a living at it. How many potential customers do you already know who are desperate for a perpetual calendar? What other features? Has it ever occurred to you that they aren't routinely available because no-one needs/wants them? With only perhaps a dozen customers per year, how will this be a practical. money-making, business when you compete with wristwatches & wall-clocks selling for well under $100? Just asking some obvious questions. If, as Mr. Salts above suggests, this is a hobby project, then I can respect that, but won't waste my time advising you. I wish you all the best...
 

MrSalts

Joined Apr 2, 2020
2,353
If, as Mr. Salts above suggests, this is a hobby project, then I can respect that, but won't waste my time advising you. I wish you all the best...
Note, some of the great Swiss watch makers started as hobbies (exhibitions of expert craftsmanship). I wasn't implying that income cannot be part of a hobby or artistic venture. I know someone who makes kinetic clock sculptures as a hobby that he sells for several thousand dollars. @jrb_sland completely misses the conceptual difference between Rolex and Timex.
 
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