Let's Make Robots!

Make a lightweight gearbox from a clock movement

Teaches an old clock a new trick

Anyone ever try to modify one of those cheap battery operated analog clock mechanisms as gear train?  It would make an extremely lightweight gearbox for small bot.

Some quick research on the web provided some insight on how these things work:


Then I tore open a broken clockwork that's been sitting around for ages. OK, I tore it open first, then did the research. ; j

The result? I was able to disassemble the mechanism, remove the coil, crystal and battery contacts, drill one small hole in the case, and I had a working lightweight gearbox. I inserted the cut off end of an electric toothbrush to propel the driven gear.

The exterior thumb wheel (originally used for settting the time) turned a bit slowly, but that was with a 3v motor. I tried stopping the thumb wheel with moderate pressure from my finger, and I couldn't do it.

I did notice the clock hands (OK, just one hand. This is from a broken clock, remember?) didn't move with the motor. It turns when I move the thumb wheel by hand, so I'm not sure what's going on there. However, I think I proved to myself this is a workable approach.

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Yes inside is a very small Stepper Motor Hacked out of a simple electronic Clock Mechanism.

They are very easy to Hack and drive with very simple hardware Microcontrollers. (and also possible with discreet componants to).

Its has one coil connected to a magnetic spindle - first you drive the coil one way with 1.5V then reverse the polarity and drive it the other - simple as that. 

Check the URL I posted in my original message. I believe it is a very tiny stepper motor, at least in most cases.  It's a coil and magnet driven by electronics and the crystal for timing.

Gareth's post makes me re-think about the possibilities of using the built in motor, with a faster clock speed and the built in driver circuit (it's under a black blob of plastic). Or maybe bypassing the circuit but keeping the stepper motor and just adding a stepper control circuit to drive the motor forwards/backwards/breaking.  As long as you are talking about a feather weight robot, this mini-stepper could be up to the task. Push it too hard or fast and I'm not surprised if it overheats as Gareth noticed. 

I have to admit i was using 4Volt pulses to drive it at the time (yes direct connected to (motor) contacts)- as my motor controller will not work below 4v . (-: more of a Big Tick and Big Tock :-).

If you pulse it fast with 4V - then delay (ie cool off period @0V) then reverse pulse it fast with 4V then all is ok - however at high frequency it will overheat (@4V)

It's encouraging to know someone else has tried this. Thanks for the advice. I gutted mine, including the coil, so I'm dependent on an external motor. I just kept the magnet and small gear from the original stepper motor.  I intend to mount that to the drive shaft of a small motor, so I can use standard motor control instead of a step motor.

If I understand you correctly, the reason you only get it to move one "tick" (or step) at a time is because that's how stepper motors work.  You have to apply voltage in the right sequence to the right pins to keep the motor rotating. Since you gutted the electronics but kept the whole stepper motor intact, you have to deal with that sequencing. I'm just using a piece of the original motor because it has the right gear size to drive the rest.

Someday I'll grab two identical clock movements and use them for propulsion on a lightweight bot.  I like the idea of a solar bot like you suggested. 

I have changed my mind ......I think its a solenoid! type motor . ie apply voltage to a coil and it fires the coil which fires a small pin to push the gear - that would make sense as to reset it you have to reverse the polarity and fire the pin back hmmmm- as there is no spring return to do this.... Can i join you in die-secting and getting to the root of this - as its been in the back of my mind too.

Such a cool mechanism waiting for an application.....

So, you're saying that there's micro solenoids waiting to be harvested inside all those small Ikea wall clocks?


Ok i am hooked -  i will disect my clock further and confirm....... these clock mechs are real cheap to buy anyway.......

Edit:- Later the same afternoon........

......... Confirmed Micro-Stepper Motor . at the heart of it all is a tiny round magnet with a tiny cog attached to it (this is why it is a light weight system - it is an amazing motor i must say - very fine engineering)

If its any Help.......

I took one apart a while ago (a working one) and you can "gut" out the electronics and just keep the stepper motor connected to the gear train.

- Yes it is a stepper motor - however the only way i could get it working was by flipflopping the power to it .... ie get a 1.5volt battery and apply it to the contacts of the stepper motor - you may here it "Tick" - then reverse the polarity and apply to the contacts again and you will here it "Tock" (if the second hand is connected its easier to watch it move).

The cool thing is it is a very light gear train - perfect for solarbot bots - i just need time to work out some simple "ticktock" electronics (however i have little time to do it ). I have driven it with my Arduino connected to a motor controller and it worksvery well indeed. (but if you push the motor coil too much it does get hot..........)