Gina

A-mazing!!!

Made a few tweaks and assembled the mechanism again from chain drive to escapement and pendulum crutch and been testing. Making progress. The escapement waggles nicely with a small pull on the chain. Next job will be to add the pendulum and mount the clock into the case to give the pendulum room to swing. Then connect a weight to the chain and see if the clock will run and if so how much weight it needs. I have a variable weight in the form of a one litre screw cap bottle to which I can add water as required.

I have lots of examples of Amazon wasteful packaging including a small box of spacers that came in a great big bag a few minutes ago but that beats anything I've received!

I had thought of having one winding motor in the middle driving both the going train and the striking train but if the motor is to go behind the back clock plate it can't be in the middle because the pendulum occupies that place. I could have the motor on the right driving the main winding sprocket and that could go on to drive the strike winding sprocket. To go behind the back plate it would have to be a NEMA14 as a NEMA17 would be too big. I shall need to confirm that the NEMA14 is powerful enough to drive the clock. Whilst it would save costs a bit to use the one motor to wind both the clock and the striking system, I could save much if not all the reduction gearing by having a separate motor for the striking part. With a separate motor it could run it much less often and save gearing or even make it match the striking sequence with suitable Arduino code. Anyway, I can look into that later, as long as I leave room.

Going train with escapement.

The striking mechanism will also have automatic winding but this case is quite different. In a period of 12 hours the clock strikes 1+2+3+4+ --- +10+11+12 = 78times. If the motor winding is constant (easier to implement) the weight will move up and down as the rotation rate of the chain wheel is not only intermittent but varies a lot over the 12 hour period. The total motion will be 78 units in 12 hours but 12 of those are in the last hour and only one in the first hour, 23 in the last two hours etc. I think the easiest way of catering for this is allow for the full 78 units of weight drop in the space inside the case. This allows a considerable safety margin, maybe unnecessarily but is a starting point. The upshot of the above is that 78 revolutions of the strike wheel would result in in the chain moving twice the weight hight range in the case. Calculating... Height of case less height of weight plus pulley/sprocket is around 1.5m Each chain link pair is 20mm Using the same design of drive sprocket as the main clock, with 18 teeth, one revolution is 18 x 20 = 360mm Total chain length for full weight range is twice weight range = 3m Number of revolutions of striking drive sprocket is therefore 3000/360 = 8.33 Allowing for the full striking sequence within the case height means 78 revs of the strike wheel corresponds to 8.33 revs of the motor sprocket Gear ratio is 78/8.33 = 9 which conveniently works out as two pairs of gear with 3:1 ratio. Now for the motor drive gearing... If I use the same design of motor sprocket with 8 teeth, that's 8x20 = 160mm of chain. Since the chain would move 3m in the 12 hours driving the strike mechanism then this amount needs winding up in that time. 3m of chain with 160mm per rev of the motor sprocket means 3000/160 turns of the sprocket in 12 hours ie. 3000/(160x12) = 1000/(160x4) In one second the sprocket wants to turn 1000/640x3600) revolutions ie. one rev in 640x3600/1000 = 64x36 = 2304 secs Motor turns once in 200s so we want a gear ratio overall of 64x36/200 = 8x36/25 boiled down to the lowest common factor That's either a lot of gears or includes a ratchet drive.

Decided to simply go for a 1:4 gear ratio rather than 4:1 on the chain drive to centre wheel gear pair. The means just 1/16th the weight required but running 16x faster. This is no problem with the stepper motor drive, in fact it's easier. Calculating... The centre wheel turns once per hour so the drive sprocket 4 times an hour or 15m per revolution. Chain drive sprocket has 18 teeth and motor sprocket 8 teeth. Motor sprocket wants to turn 18/8 times in 15m or 18x4/8 = 9 times an hour ie. 9/60 = 3/20rpm or 20/3 mins/rev which is 20x60/3 = 400 secs/rev I expect to use a NEMA17 or maybe NEMA14 stepper motor with 200 steps/rev. If I were to use 1 step/sec motor speed the motor shaft would rotate at 200 secs/rev I plan to drive the motor sprocket with a pair of spur gears from the stepper motor so the ratio would be 2:1 - very convenient.

Very happy with my ZWO EFWmini.

The gears seem to be alright now but there is still too much friction. It would need several kilos weight to drive the clock even without the escapement. I think I need to reduce the gear ratio between chain drive sprocket and centre wheel.

As you probably know, I use the Raspberry Pi which costs about £30 from Amazon, with free (open source) software. I have all the information for using this and have posted it on here in Blogs.

You can get the ZWO ASI 120MC-S camera plus fisheye lens from FLO for £146 plus carriage. Not quite all sky but a good amount. It all depends on how much you want to spend.

The centre wheel and the intermediate wheel were both at fault and I'm reprinting both.

Going train with escapement assembled into the two acrylic plates. Unfortunately it's binding somewhere and won't run. Have to take it apart again and reassemble in stages until I find the problem. This is the clock mechanism out of the case. The pink part takes the drive chain.

Printed the crutch and tried to assemble it all but found the anchor wouldn't fit so redesigned it and just finished printing it.

Now printing the brackets which hold the bearings for the anchor shaft and pendulum suspension.

Strange, there shouldn't be much difference between f1.8 and f2. OTOH I found the Fujinon fish-eye lens 1.4mm and f1.8 let in a lot more light than the 1.55mm f2 lens which is considerably smaller. I suspect focal ratios on fish-eye lenses mean something different from "normal" lenses and telescopes.

Tests with that escapement seem favourable so I'm going ahead with the construction.

Yes, I get that too. Well, similar.

Ah yes, 3D printers, very useful but a whole new "can o' worms" 😁

I've definitely got far too many projects but most are just shelved.

Might get back to my ASC soon. I tend to swap around with my projects, doing a bit on one then getting tired of it and going on to another. Guess I have a "grasshopper mind" 😁

I shall be interested to see the night sky (if you have any left this side of the solstice - just 3 nights left here before we lose astronomical darkness altogether).

That's a lot better.

That's not bad considering your equipment The moon has just risen over yonder hill here. A lovely deep orange colour.

Yes, that is a good price and probably well worth it for what you get and the saving of effort. I'm finding that applies to a number of things.