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Author Topic: Why does my clock run backwards?  (Read 8850 times)

Offline wolfekeeper

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Why does my clock run backwards?
« on: 10/03/2013 01:35:58 »
Following instructions from the internet I took a clock, and opened it up, took apart the mechanism, and just flipped over a tiny piece of metal inside, and then, with difficulty, reassembled it again, and it now runs backwards.

I thought this was fun.

But what I don't know is why flipping over this piece of metal has this effect.

What type of motor is this, and why does flipping over this piece of metal do that?

The piece of metal seemed to be soft iron, it certainly didn't seem to be an electrical connection.
« Last Edit: 14/03/2013 04:04:41 by chris »


 

Offline CliffordK

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Re: Why does my clock run backwards.
« Reply #1 on: 10/03/2013 02:11:19 »
If the piece of metal was a battery, that might make a difference.

Otherwise a photo and description of which piece of metal you flipped would be helpful.

I assume many clocks that tick have some kind of a ratchet that would generally be unidirectional.
 

Offline Joe L. Ogan

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Re: Why does my clock run backwards.
« Reply #2 on: 10/03/2013 02:11:35 »
I would like to make a few puns about this but I shall refrain because you may not appreciate my sense of humor.  Thanks for comments.  Joe L. Ogan
 

Offline wolfekeeper

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Re: Why does my clock run backwards.
« Reply #3 on: 10/03/2013 02:48:33 »
You flip over the U-shaped piece here:

http://www.instructables.com/id/Reverse-Clock-1/step5/Step-411/

It doesn't seem to be a ratchet, the piece doesn't seem to physically move.
 

Offline CliffordK

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Re: Why does my clock run backwards.
« Reply #4 on: 10/03/2013 04:47:41 »
A most unique shape of bar.

Here is my interpretation.  This is the business end of a stepper motor.  On a regular interval, the polarity of the electromagnet is reversed, for example perhaps once a second, forcing the magnet in the middle to rotation (it is a magnet, right?)

What it needs is a simple way to favor the rotation in one direction of rotation over the other.

My guess is that the notch in the end of the bar is the critical component.



This notch will create a slight asymmetry in the magnetic field, weaker on the notched side than the other.  And, thus the magnet in the middle of the motor won't sit straight, and pulls it predominantly in one direction.

Assuming this is a "junk" clock, what I would do is cut where I marked it in red.  Doing so should compensate for the inequality in the magnetic field in the opposite direction, and also reverse the clock.

I would leave the pin hole, just to help hold everything in place.

Take some pictures so you can post a response.

« Last Edit: 10/03/2013 04:49:17 by CliffordK »
 

Offline wolfekeeper

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Re: Why does my clock run backwards.
« Reply #5 on: 10/03/2013 13:44:07 »
I didn't have any easy way to check, but I wondered if the spinny bit might be multipolar.
 

Offline SeanB

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Re: Why does my clock run backwards.
« Reply #6 on: 12/03/2013 19:05:49 »
It is a magnet polarised normal to the axle, so that it will be affected by the pole pieces. A pulse is applied to the electromagnet one a second ( or 8 times a second in a so called continuous clock) and the polarity is swapped every pulse. thus the magnet is attracted to the poles an lines up, but the inertia causes it to overshoot slightly so that next time it will carry on in the same direction. You flip the core over and the place where it rests due to attraction to the steel core moves as well, and it will then run the other way, though to it it always turns in the same direction.
 

The Naked Scientists Forum

Re: Why does my clock run backwards.
« Reply #6 on: 12/03/2013 19:05:49 »

 

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