A prototype Lavet stepper motor

[John HaineParticipant @johnhaine32865]

Is the rotor 2 pole or 4 Duncan?

[John HaineParticipant @johnhaine32865]

Another photo gleaned from the web.

[Tony JeffreeParticipant @tonyjeffree56510]

Think I have it figured out now – the asymmetry comes from the shape of the pole pieces on the rotor (rather than the shape of the pole pieces on the electromagnet) which is interesting. Potentially one could develop the same approach with any number of poles (but with correspondingly more difficulty in construction).

I suspect it may be time I resurrected my CNC mill, which has been out of service since the move!

Edited By Tony Jeffree on 26/03/2021 14:08:22

[duncan webster 1Participant @duncanwebster1]

4 poles as far as I can see, then 30 teeth on the white wheel gives 1:4*30 = 1:120 reduction to drive minute hand at 30 second intervals.

Tony's explanation sounds about right, I think with a bit of thought at jig to fit on the rotary table could be devised to make the pole pieces. I'm loathe to start dismantling mine to measure it in detail, I might put a posting on the Synchronome site top see if anyone has a scrapper. If nothing else having one which worked off less than 24v would be handy

[Tony JeffreeParticipant @tonyjeffree56510]

I'm sure that rolling your own 4 pole Lavet motor would be do-able. I've just received my order of donut-shaped magnets – diametrically magnetised, 6mm diam, 3mm ID, 1mm thick, so my next try will be to re-make a 2-pole motor using one of those – should end up being smaller and quieter than this first attempt. After that I fancy having a go at a 4-pole just to see what can be done.

[John HaineParticipant @johnhaine32865]

Breath bated here Tony! This is really interesting as I'm re-planning the next clock and would much prefer to make the movement, but would rather avoid an ordinary bipolar stepper.

[Tony JeffreeParticipant @tonyjeffree56510]

I agree John – the Lavet-style of motor has its attractions, not least being the ease of driving it.

[Michael GilliganParticipant @michaelgilligan61133]

Gents [no pun intended] …

Did you look at the original French patent that I linked yesterday ?

Lines 18 to 20 on page 2 read:

Les fig. 8 à 10 représentent un petit
mouvement de récepteur horaire du type à
émissions inversées toutes les 1/2 minut;

… which translates to:

Figs. 8 to 10 represent a small
clockwise receiver movement of the type to
reverse transmissions every 1/2 minute;

… and I think those figures are worth a look.

MichaelG.

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Edit: __ here’s a bonus : I think this is Gent’s patent describing the essence of Duncan’s motor

https://worldwide.espacenet.com/patent/search?q=pn%3DGB604840A

Edited By Michael Gilligan on 26/03/2021 23:44:38

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by duncan webster on 26/03/2021 11:27:15:

Here's a couple of pictures of the Gent's, definitely 4 pole and 1/4 rev per pulse. The white gear is driven by a worm on the motor shaft. It is very quiet

Duncan – any chance of posting a dimension or two, for example the dimensions of the U-shaped pole piece or the coil, so I can get an idea of the size of the components?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 26/03/2021 23:13:16:

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Edit: __ here’s a bonus : I think this is Gent’s patent describing the essence of Duncan’s motor

**LINK**

 

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As the saying goes : You can lead a horse to water …

MichaelG.

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Edit: __ Yes … it includes some relevant dimensions

Edited By Michael Gilligan on 27/03/2021 09:11:53

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Michael Gilligan on 27/03/2021 08:59:29:

Posted by Michael Gilligan on 26/03/2021 23:13:16:

.

Edit: __ here’s a bonus : I think this is Gent’s patent describing the essence of Duncan’s motor

**LINK**

.

As the saying goes : You can lead a horse to water …

MichaelG.

Yes, saw that, thanks, but no dimensions that o could see…?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Tony Jeffree on 27/03/2021 09:08:53:

[…]

Yes, saw that, thanks, but no dimensions that o could see…?

.

Try going to line 10 on page 3, Tony

MichaelG.

[John HaineParticipant @johnhaine32865]

The magnet is a disc 5/8" dia and 5/32" thick. Everything should scale from that.

[duncan webster 1Participant @duncanwebster1]

I'll measure it up later on, but if you are in the North West you could borrow it

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Michael Gilligan on 27/03/2021 09:17:46:

Posted by Tony Jeffree on 27/03/2021 09:08:53:

[…]

Yes, saw that, thanks, but no dimensions that o could see…?

.

Try going to line 10 on page 3, Tony

MichaelG.

Thanks Michael – I couldn't get to the text when I looked on my mobile for some reason. Not the easiest site to navigate!

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by John Haine on 27/03/2021 09:45:49:

The magnet is a disc 5/8" dia and 5/32" thick. Everything should scale from that.

Perfect – thanks.

[duncan webster 1Participant @duncanwebster1]

The bent up arms are 8 * 3.4

Across the outside they are 33

The bobbin is 25 dia * 28

The gap from arms to rotor unenergised is <1

The offset of the rotor is <1

Any more just shout

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by duncan webster on 27/03/2021 12:53:19:

The bent up arms are 8 * 3.4

Across the outside they are 33

The bobbin is 25 dia * 28

The gap from arms to rotor unenergised is <1

The offset of the rotor is <1

Any more just shout

Thanks Duncan – that's great!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Tony Jeffree on 27/03/2021 11:32:19:

[…]

Thanks Michael – I couldn't get to the text when I looked on my mobile for some reason. Not the easiest site to navigate!

.

Sorry, Tony … I should have explained:

Near the top right corner of the linked page is a vertical column of three dots

Click that to open a menu … one option is Download PDF

MichaelG.

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Michael Gilligan on 27/03/2021 13:47:07:

Posted by Tony Jeffree on 27/03/2021 11:32:19:

[…]

Thanks Michael – I couldn't get to the text when I looked on my mobile for some reason. Not the easiest site to navigate!

.

Sorry, Tony … I should have explained:

Near the top right corner of the linked page is a vertical column of three dots

Click that to open a menu … one option is Download PDF

MichaelG.

No problem Michael – it was much easier to find on the laptop & I now have a paper copy of the whole patent to peruse – thanks.

[Tony JeffreeParticipant @tonyjeffree56510]

Makes an interesting read. It seems that the rotor can have any (even) number of arms on each side, so in principle you could make one with 30 arms top and bottom that would give 60 pulses per rev, which would be handy, although the machining for that would need to be very precise indeed (or built rather larger).

[Tony JeffreeParticipant @tonyjeffree56510]

Of course, if you were to build two 60-step motors and one 12-step…there would be no need for gears…Hmmmm.

[duncan webster 1Participant @duncanwebster1]

But that would mean that at 5 to 3 (for instance) the hour hand would be resolutely pointing to 2. Better to build 2 off 60 step motors and only pulse the hour one once every 5 minutes.

It might actually be easier to make a 2 phase stepper with 60 notches per rev, the only extra is another coil I think, and the rotor is simpler, just cylindrical rather than the snail shape

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by duncan webster on 27/03/2021 16:40:55:

But that would mean that at 5 to 3 (for instance) the hour hand would be resolutely pointing to 2. Better to build 2 off 60 step motors and only pulse the hour one once every 5 minutes.

It might actually be easier to make a 2 phase stepper with 60 notches per rev, the only extra is another coil I think, and the rotor is simpler, just cylindrical rather than the snail shape

No necessity to use hands, of course, you could use a digital style HH MM SS display.

Edited By Tony Jeffree on 27/03/2021 16:59:58

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 26/03/2021 12:48:48:

Another photo gleaned from the web.

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I’m having some difficulty interpreting the ‘perspective’ sketches in the patent …

it is reasonably clear from this photo, and from Fig.1, that items 10 and 11 are cut from a closed tube shape … but Fig.3 and Fig.4 [which purport to clarify things] appear to show them cut from flat plate.

Is this an over-simplified sketch, or an optical illusion ?

… what do they really look like ?

MichaelG.

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