Moon Dial Clock showing realistic moon phase - 3D printed

[Gina]

It's not really a blue moon, it's lit with a white LED but the digital photo has coloured it blue

[Gina]

This is basically a standard clock with the gears 3D printed and driven by a stepper motor controlled by a Real Time Clock module connected to an Arduino but what makes this clock different from most is the moon phase dial on the top.  Many longcase (Grandfather) clocks have a moon phase dial but this is a simple disc with a picture og the full moon with two semicircles to obscure it.  Here's an example.

http://www.allansmithantiqueclocks.co.uk/Images/uploaded/LCMAH353dial.jpg

What I was wanting was a better moon display with a more realistic moon phase.

http://www.masterclockrepair.com/images/675_moon_phase_crop.jpg

Initially this didn't seem possible.  The curve of the terminator changes from a half circle at "new" and "old" moon to a straight line at half-moon ie. first and last quarter.  There are clocks with separate pictures forthe various moon phases but I wanted just one dial.

In reality, the moon is lit with light from the sun at various angles and my first idea was to simulate the sun with an LED on an arm rotating with axle centred on a moon globe.  This turned out to be impractical.

Next idea was to take a sphere constructed form two hemispheres - one white and one black.

This would give  pretty good representation of the moon phase.  I wasn't needing the structure of the moon - just a dial simulation.  This sort of worked but wasn't good in dim light so I considered lighting it.  I could have used a floodlight as used for lighting paintings but found shadows a nuisance.  The other problem was that the black plastic was too shiny (matte black wasn't available then).

Then I thought "the white part is translucent plastic - I can light it from inside".  But the globe rotates continuously so getting power to an LED inside would need slip-rings.  My previous experience of making and using slip-rings for power was far from good so didn't like that idea.

Eventually, I came up with the idea of a fixed, white moon globe and a hemispherical shield or cover arranged to rotate around the globe.  I knew I could arrange this mechanically by using a tube within a tube as used for the hands of clocks. Wiring for an LED could go up inside a tube holding the globe and then another tube outside of that would hold the shield.  The outer tube could be driven by a gear.  I'll post details of this later.

More details coming up...

[Gina]

Problem with a couple of images above

[Gina]

These are the missing images.

[Gina]

Here are a couple of screenshots of SketchUp model of the moon phase dial.  Coloured to show the components.  In reality the shield is black and rest white.

[Gina]

Some photos of the moon phase dial production.

       

[Gina]

The lighting for the moon.  White LED with 3D printed diffuser.  Led fixed with hot melt glue.

Result

The shield blocks the light quite well.
 

Here's an early version of the clock.
 

[Carastro]

You never cease to amaze me Gina.  I thought making of a clock was clever enough, but to add a Moon Phase like this is incredible.

Carole  

[Gina]

Thank you Carole ? 

Before I get on the the design of the main parts of the clock there's the question of the rate at which to turn the moon dial.  This is usually considered to be 28 days but that's only an approximation and if I were to use that the moon phase would quite soon be wrong.  The moon phase repeats repeats every 29.53 days. 

I found this talking about a more accurate moon phase dial as used in very high quality watches :-
 "30:90,32:90, approximates the synodic month as 29.53125 days. The 30-tooth wheel is on the day-of-the-week shaft which is   incremented once a day at local midnight by a ratchet, thus turning at 1/7th of a turn per day. The second 90-tooth wheel is on the edge of the lunar display disk, and turns at 1/59.0625th of a turn per day, producing an error of 1 day in 122 years."

In my case a pair of spur gears drive the moon phase dial, having a ratio of 96:135.  A ratchet wheel on the same shaft as the 96 tooth gear is advanced one notch every 12 hours with a lever and cam system from the hour shaft.  The ratchet wheel has 42 teeth.  The calculation of the period of the moon phase goes like this :-
        The lever system advances the ratchet wheel one tooth every 12 hours giving a period of 21 days.
        The gear ratio of 96:135 further increases the period to 21x135/96 = 29.53125 days

[Padraic M]

Fantastic! How many clones of Gina have you made? Because there is obviously more than one of you. Your productivity is remarkable!

[Gina]

Thank you Padraic ?   There is, however, just one of me.  I could do with a twin or clones with all the projects I have on the books!!!!  (Wish I could type without mistakes!!)

The above shows the advantage of 3D printing.  Gears of almost any number of teeth can be designed and printed.  Unlike metal, the teeth need to be reasonably wide so my 3D printed clocks tend to be much bigger than conventional clocks.  In fact my biggest clock has a dial 3ft diameter and largest wheel of 330mm (13").  This is also finished and working and will be the subject of another thread.

[Gina]

The main casing an structure of the clock is plywood with a picture frame as the frame around the face.  The moon phase dial cover was 3D printed.  The actual face carrying the dial and numbers is clear acrylic sheet 12" square.  Dial, numbers and hands were 3D printed.  I'll come to the box construction later.

  

It may be seen that this earlier design had the gears in a row and piled on top of each other.  I decided, however that the works would look better if the gears were spread out more like the gear train of a conventional clock and that's what we have as the final design.  In either case the number of gears is the same.

As I mentioned earlier, the clock is driven by a stepper motor and the first stage is a pair of gears to drive the seconds shaft and the sweep seconds hand.  Next a gear ratio of 60:1 is needed to drive the minutes shaft (and minute hand) and finally 12:1 to drive the hours shaft (and hour hand).  The hour shaft - or rather tube - has a cam on it that drives the moon phase mechanism.  A 3D printed gear train needs more gears than metal gears as it's difficult to produce tiny pinions in plastic. The 60:1 seconds to minutes is achieved with three reductions of 5:1, 4:1 and 3:1.  The 12:1 minutes to hours has 4:1and 3:1.

Another difference is that normal clocks have metal axles running in holes in brass plates as bearings.  This clock reverses that and has the bearings in the gears - ball bearings make this easier.  The exception is the gears that drive the hands.

This shows the gears separated.

This is the seconds shaft with drive gear and bearings.  The shaft is 5mm dianeter.
 

The 60:1 gear reduction plus motor drive.
https://stargazerslounge.com/uploads/monthly_2016_05/573cbe981cdbb_NewSMGears05.thumb.JPG.194d86ead2c673da316171de97121b1f.JPG

12:1 reduction gears added above the others plus lever system for the moon phase dial.

[Gina]

Now to the woodwork and fitting the bits in.

Modelled in SketchUp.

Photos of the construction.

      

[ApophisAstros]

You are so clever Gina , Bravo,

Roger

[Gina]

I think that concludes the non-technical aspects.  There is another feature which this clock has and that's automatic time setting.  The minute and hour hands have tiny magnets embedded in the ends and there are Hall effect devices which detect when the hands are at 12 o'clock.  This allows the clock to be advanced and the positions of the hands detected.  Using the Real Time Clock data and some calculations the clock can be set to the right time whenever it is powered up - automatically.

Hall device for hour hand.  Wires hidden behind the 12.
 

Hall device for the minute hand added and wires taken up and away from the dial.

Thin black cable is hardly noticeable.

[Gina]

The way the auto time setting works is that the real time is read from the RTC by the software and the motor is run many times faster than normal.  The hour hand sensor is checked first as this is triggered a bit before the minute hand gets to the top.  The motor speed is reduced so that the minute sensor is easily and precisely triggered when the minute hand is at the 12 o'clock position.  Taking this 12 o'clock motor position the amount of motion required for the hands to reach the correct position is calculated from the Real Time Clock and the motor is run fast until this position is reached.  Correction for the time this takes is calculated and taken into account.

[MarkAR]

Superb work Gina.

[Gina]

Thank you Mark ? 

[Stub Mandrel]

I did enjoy following that project's ups and downs, nice to know it's still working!

[Jkulin]

Gina, as Carole says, you never cease to amaze me.

For other members that don't know, Gina is a retired engineer (I think) and posts these projects up to inspire people, she is a lovely knowledgable person and I wish I had just one ounce (25gms in today's money) of her abilities.

Keep them coming Gina! ? 

[Gina]

Thank you very much John ?   I'm sure you too have plenty of abilities in different fields.  I am a retired electronics engineer and computer programmer.  This sort of stuff has been my "bread and butter" all my life (apart from being a housewife and a carer).  I have my father to thank for getting me into it at an early age and paying for me to have a good education, culminating in University though I fell just short of getting an Honours BSc.  See, I'm not brilliant!!

 

[Gina]

There is a lot more to this project - mostly technical - and it was far from easy.  I'm wondering how much more to post here.  There is some maths involved and, of course, programming the Arduino to carry out all the functions.  I am happy to post as much as our members would like.

[Gina]

Posted by: @stub-mandrel

I did enjoy following that project's ups and downs, nice to know it's still working!

Thank you Neil ? 

 

[Gina]

One thing I will add is that the clock face is lit by a string of RGB LEDs around the edge.  The colour ratio was determined by experiment.

[Gina]

When "changing the clocks" (BST to GMT) something went wrong and it seems the Arduino Nano blew up so I need to make repairs.

In view of this I plan to take advantage of the fact and upgrade the clock to a more efficient setting up and GMT/BST change procedure.  This will involve changing to an ESP32 and controlling the clock from my main computer.