I would like to make a locket swing back and forth like a pendulum for a long time on little power, like some battery operated clocks (my grandmother has one that runs for months or maybe even a year on a single AA cell) but without anything to display time (the smaller the mechanism the better). What's the simplest way to achieve this in a small form factor that can be easily hidden?

 

smaller the better? mems

 

It's hard to say with that information. Perhaps something like this. You'll have to filter the results to suit you.

https://www.ebay.com/sch/i.html?_fr...nt.TRS0&_nkw=pendulum+clock+movement&_sacat=0

The AA battery I use on my large wall clock last more than two years.

 

I don't really want to use a clock movement because I think it has unnecessary bulk pertaining to moving the hands around. Ideally, the electromechanical part would be at the top and I could put the battery and the rest at the bottom.

 

A pendulum, sans friction, will swing indefinitely at its resonant frequency, requiring no additional power except for the initial impulse to get it started.

Friction makes it run down over time. In the real world, energy must be applied to overcome friction.

So, first, design your pendulum such that it exhibits as little friction as possible.

Second, develop a scheme where you can add a pulse of energy at the resonant frequency and in phase with the motion of the pendulum -- i.e. positive feedback.

You can do this with a small coil and magnet and a low power CMOS timer tuned close to the resonant frequency.

A really clever design would maintain info about the phase and amplitude of the pendulum and apply energy only when and if needed.

 

And I found this:

 

You could get a small clock mechanism with a pendulum and remove the clock mechanism as the pendulum has its own separate circuit.
One such mechanism I had used a separate battery for the pendulum.

 

https://www.ebay.com/itm/Pendulum-D...856391?hash=item1c7baa8287:g:yFMAAOSwpLNX7aSm

 

I don't think I can use a regular clock mechanism because it's pretty large and I won't be able to hide it. I made this kind of rubbish image below to show what I'd like to achieve. I'd have liked the pendulum bob to not have to get so close to the base but I'm not sure I can find a way around that. I'm not going to have space in the bob for a large magnet.

I think Joey's circuit is the cloest to something I can use re: hiding the stuff that makes it work. Thanks for everyone's responses though and sorry for not being clearer in the first case.

 

I don't think I can use a regular clock mechanism because it's pretty large and I won't be able to hide it. I made this kind of rubbish image below to show what I'd like to achieve. I'd have liked the pendulum bob to not have to get so close to the base but I'm not sure I can find a way around that. I'm not going to have space in the bob for a large magnet.

I think Joey's circuit is the cloest to something I can use re: hiding the stuff that makes it work. Thanks for everyone's responses though and sorry for not being clearer in the first case.

Google "Pendulum Movement". You may find something else useful.

 

Here's another design of interest.

 

And I found this:

I picked one of these up to amuse the grand kids, it appears to work on the same principle, it will work for a week if you let go.
Top-Secret-Mystery-Magnetic-Spinning-Peg-Toy-Gyroscope-Spinning-Spin-Toy-/ ebay 252760622261
It could be adapted, it appears to use the same M. Faraday principle as the brass bolt that spins the nut off.
The gyro is just a coil pulsed by a prox sensor.
Max.

 

Using a couple razor blades to support a "U-Bar", hang the pendulum from the bar that is resting on the blades. The friction from that will be nearly zero. As long as the pendulum is not too heavy, this will work pretty well. There's also "AIR" friction. If you want you can mount this assembly in a vacuum.

At one end of the swing mount a photo transistor connected to an amplifier decoupled through a capacitor, so that when the light level changes drastically (from the shadow of the pendulum) the electro magnet positioned just above the top of the swing should come on for that brief period. As long as the magnet is not strong enough to attract and hold the pendulum, the pen' will swing away, but only after having received a slightly higher elevation due to the momentary magnetic force. And the magnet should only be pulsed long enough to attract the pen' but not restrict it on it's way back down.

 

If you want you can mount this assembly in a vacuum.

You realize maintaining a vacuum will kill his energy budget, no?

Unless, of course, the assembly is hermetically sealed and he implements a getter.

 

You realize maintaining a vacuum will kill his energy budget, no?

Yes I know. Just pointing out as many forms of friction as I can think of.

 

Add a 1.5 V AA cell. Abundant at the 99 cent stores :

----> https://duckduckgo.com/?q=solar+dancing+toys&t=canonical&iar=images&iax=images&ia=images

You may click on 'Videos'

 

Add a 1.5 V AA cell. Abundant at the 99 cent stores :

----> https://duckduckgo.com/?q=solar+dancing+toys&t=canonical&iar=images&iax=images&ia=images

You may click on 'Videos'

I was looking for those as well to help the OP with ideas, but I didn't know what to search for.

Good job.

 

Thanks; I've ordered one of these toys from China and I'll dismantle it when it arrives although I think it might be underpowered. I also wonder how to attach the chain to the post at the top to minimise friction so it swings as far as possible.

 

Thanks; I've ordered one of these toys from China and I'll dismantle it when it arrives although I think it might be underpowered. I also wonder how to attach the chain to the post at the top to minimise friction so it swings as far as possible.

A light chain is likely to have near zero mechanical resistance to start with. I don't think that is an issue.

 

A light chain is likely to have near zero mechanical resistance to start with. I don't think that is an issue.

Well I can't do anything about the air resistance and I'm guessing it just isn't going to swing far but I won't know for the few weeks it takes to get this thing from China. I've got a couple other projects to work on in the meantime.