Gina

To use this mechanical perpetual calendar as the project stands would not need a Real Time Clock, just a source of good timekeeping such as the 50Hz mains frequency.  This would simply need counting for 50x60x60x24 to produce action every 24 hours.  The action would consist of creating sufficient stepper motor steps to rotate the cams one revolution.  The 50Hz input would use interrupts to avoid the stepper code from causing missed counts from the 50Hz.  Of course, the Arduino sketch would need synchronising with real time so that the calendar advance occurs at midnight.  A simple push button pressed just once at midnight one day could do this.

I guess it's time I described how the 31 days is converted into the day-of-month in terms of two decimal digits and how the weekday and month are driven

The basic principle uses gears with missing teeth where no motion is to be transferred to a pinion on the drum.  eg. for the units the counting is one-to-one until we get to the end of the month at day 31 and the units show "1" but the next position corresponds to the first day of the next month so instead of going from "1" to "2" it needs to stay at "1" so the tooth that would turn the pinion is missed out and the units drum stays showing "1".

For the tens digit of the day-of-month, the drum wants to show zero or a space until the day reaches 10 when the tens digit wants advancing to show a "1".  So no teeth for 1-9 then a tooth at 10 turns the tens drum one digit.  From 11-19, again the drum must stay at "1" but a tooth at 20 moves it on to display "2".  Same again from 21-29, no teeth, but one at 30 to move the drum on to show "3".  Finally, when the date goes from 31 to 1 the tens drum needs moving onwards to show "0" or a space so here we have a tooth.

To advance the month, one single tooth where the date goes from 31 to 1 engages with a pinion on the month drum to advance it to the next month.  The months drum pinion has 12 teeth for the 12 months in the year.  The units of date has 10 teeth (no surprise there) but the tens doesn't have 4, it has 8 because a 4 tooth pinion would not work - the tens drum has two sets of 0123 and 8 positions.

The day-of week drum has a ratchet with 7 teeth.

Here's a collection of photos and diagrams that show the principle and test rigs.  These also show that where no teeth are required the "gear" can be reduced to just what's needed to carry the wanted teeth.

To go off at a bit of a tangent, I've been thinking of much easier alternatives, interesting though this purely mechanical perpetual calendar might be.  The original thinking was as part of a mechanical clock with the only modern workings being auto-winding.  In that aspect this made perfect sense.  But if I'm driving the calendar off an RTC with all its facilities, maybe it's daft to just use the change of date to trigger the mechanism.  All the "clever stuff" of differing numbers of days in months could be handled in code quite easily.

I could make the mechanical perpetual calendar part of another clock project with just the simplest electronics.  For example, the 50Hz mains frequency could be used to time an Arduino which would then drive a stepper motor at a constant speed.  Since the mains supply is maintained to the accuracy of an atomic clock over a 24hr period the clock would keep perfect time - even better than using an RTC or quartz crystal.

It would be possible to make maximum use of an RTC and reduce the mechanical parts to a minimum even with a mechanical display.  The reason for wanting a mechanical display is to provide a large and easily seen display under all normal lighting conditions from full sunlight to electric light in the evening.  The best/easiest way of doing this seems to be to use drums with numbers and letters glued on.  In the past I have investigated and experimented with various types of display and the drum approach won out.

The minimal mechanical approach would be to use stepper motors to drive each drum, which means four of them.  Next would probably be to use the layshaft as in this project but driven directly (through gearing) by a single stepper motor, plus another for the day-of-week.  This relies on the special type gears used to turn the drums correctly.  I shall explain this shortly as I realise I have not done so yet.  The layshaft gearing has 31 teeth per revolution and is simply advanced one tooth at each midnight, except at the end of the month when it needs to be moved on extra notches for all months without 31 days.

The end-of-month pawl (purple) wants a better shaped tip to fit the tooth.

More parts mounted and the opportunity to test the date advance.  Note - there is some distortion due to wide angle lens.

Some of the parts mounted on an acrylic sheet.  The combined hanging levers as springs may not work.  The main date drive bar one certainly doesn't work - there's far too much movement for that length.  The month drive one might work but I'm not at that stage yet.

This is as far as I could go without being able to mount things and check for clashes.

There's been a delay in the delivery of the picture frame and until I get it I can't establish the exact dimensions of the box sides or back so since I think I currently have more chance of success in proceeding with this project than with the longcase clock and I want a working calendar to use, I shall make use of the old acrylic sheets and the framework to further this project at the expense of the longcase clock.  I already have my moon globe clock so the longcase can wait. 

I think I've gone as far as I can without fastening things to a solid base and using bolts to carry wheels etc.

Latest photo of the parts I've designed and printed so far (not including the display drums).  It's not an easy project but I'm gradually getting there

Here's a new calendar diagram showing the cams and link bars etc.  The months advance bar will cross in front of the date wheel ending in a pawl to drive the months wheel and a hanger link.  I may make the latter a spring rather than a free rotating lever.

I've come to the conclusion that the cams don't need a steady reduction from maximum to minimum and that snail cams with a sudden drop would be alright and save the rotation angle needed for a slow drop.  This means the whole 90° left from the date advance can be used to push the months wheel one step.

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Calculations for main date drive cam :-

1. Height range required is between 40mm and 50mm.  Try 46mm with max radius = 60mm and min = 14mm.
2. Operation of main date drive is something like between 0° and 270°  (¾ of full cycle)
3. Starting at 10°
4. Dropping to minimum at 40°
5. Rising from minimum to maximum between 40° and 270°.  Range = 270°-40° = 230° -  Motion = 60-14 = 46mm.  2mm per 10°.
6. Stays at maximum for rest of cycle.

Edited to give easier values to work with.

Here is a linear representation of the motion of the date advance (top graph) and month advance (bottom graph).  The top graph shows the effect of the notch depth representing the number of days in the month.  The bottom either month advance or not.

The sequence of operations is as follows :-

We'll start with date advance bar fully right with the cam follower on the top of the cam.  This would be as in the photo above.  The month advance bar would also be fully right.

1. The date cam lets the date advance bar travel back until the purple probe contacts the slotted month wheel.
2. The cam then pushes the date bar fully to the right again, advancing the date.
3. The date bar then remains in this position for the rest of the cycle.
4. Next the month advance cam follower is moved to the left until either the month probe comes into contact with the date wheel or finds the slot.  Until the slot is in line the cam follower and month advance mechanism stops there but if the slot is in line the month advance moves left pulling the month advance pawl back a notch on the month wheel.
5. Finally the month advance is pushed fully to the right and depending on whether the probe found the slot or not, advances the month wheel one month.

This is just one possible starting point and another would be to start with the date bar to the left with the purple probe resting on the month wheel or in a slot but this would stop the mechanism being manually set up.  Better for the systems to test how much or whether to advance the wheels first.  This would allow the perpetual calendar to be set to the right date manually as the mechanism has no actual date input.

Manual setup would consist of turning the day-of-week drum, then the main date wheel to the day-of-month and finally both the month wheel and the month drum would be set up.  If I get the gears that drive the tens and units of date drums in sync with the date wheel, turning the date wheel should indicate the right numbers.

Small changes today.  Redesign and new colour for the cross bar and new colour for the everyday advance pawl.  The same bolt that holds the ball bearing cam follower will also take the support lever pivot. 

I haven't yet decided on the levers and bars to advance the months wheel but I have been thinking about the cam for advancing the date wheel.  I plan to use a stepper motor to drive the cams rather than weight with flyfan governor so the cams can be a bit simpler.  OK, I know I could make things simpler by just driving the drums directly with stepper motors controlled with Arduino and RTC but that's not as much fun   I shall use just one stepper motor that will rotate the cams by one revolution at midnight each day.

Driving the months wheel requires very little force compared with the date wheel which in turn drives 3 of the 4 drums so more of the 360° can be devoted to the date drive.  Previously it was half and half.  The date advance uses up to 40mm - 10mm per day - the 40mm applies to February with 28 days.  The months advance requires only 7mm movement of the advance pawl and only needs enough force to overcome the bearing resistance and detent spring (not made yet).

I've ordered a picture frame for the front :- 16 x 12-inch Picture Photo Frame, Black to match my moon dial and longcase clocks.  The box will consist of pieces of floorboard for the sides with mitred corners and 6mm mahogany plywood for the back - I have these in stock.  I'm hoping I can get away with mounting all the parts on the back panel.

Gradually printing parts.  The glass plate on my Pilot printer has cracked but I think the printer is still usable.  Here is a photo of where I am ATM with printing the parts.

Mostly assembled the frame but didn't order the uprights for the X rails and accompanying corner brackets.  I think I am missing a couple of grub screws from the brackets I have but I guess it's possible that they escaped and landed on the floor somewhere.

Now printing new parts.

The above parts have arrived so I can start assembling the frame.

Not up to me, of course, but I see what you mean   And an 8 day week would make lots of things simpler   

Shorter axle for the drums.  Will now fit in 400mm x 300mm (or 15" x 12") box internal dimensions.

Another rearrangement that I think will be better.  The above diagram didn't have the lever proportions right - the one below is to scale.  The photo shows roughly the positions of most of the parts.  Some parts need reprinting either reversed or changed in size.