Gina

Thinking of doing a bit more to this project as astro is grinding to a halt due to the weather.  Thing is...  Can I break my addiction to astro imaging????

On 07/07/2020 at 16:54, Julessilver said:

Very comprehensive list. What software are you running on the Pi to control the ZWO?

INDI as in KStars/Ekos/INDI.  The Pi runs the indiserver and INDI drivers.

On 19/06/2020 at 10:40, silentrunning said:

Hi Gina

I'm looking at getting the dome you mention in your parts list and wondered whether you recommend it. I have purchased some cheapo ones before when I was messing around trying to build an ASC and they were very poor quality at least for this application, introduced way to much distortion.

Thanks

These domes produce negligible distortion.  I too have tried cheaper ones in the past and had that problem.

I'm wondering if I can use the timing belt to drive the going train.  That would save some space.

Printing the arms.  This shows the arms fitted on the print bed in the slicer.

Assembly.

Showing "push pin" and pallet detail.

New 72t timing pulley fitted belt just fine.

Combined escape wheel with 72t timing pulley.

Showing that timing belt just clears "push pins".

The 72t timing pulley teeth are slightly out by 1.5% by my calculation using high power magnifier.

I think driving the escape wheel with the timing belt should be quite feasible.  That will mean only a lightweight gear train will be needed to drive the hands.

That wasn't very good and too small really so I've gone for twice the size and 72t.

Making a test print of 36t timing pulley.

Going to test a couple of ideas...

Let's see if timing belt drive to the escape wheel is feasible.

• Trying a 20t timing pulley on the seconds arbour.
• a 60t pulley on the auto-winding motor would mean 180s per rotation of motor shaft
• as compared with 200s period for one step per second

Hmm...  not very clever that!!!

• trying 18t timing pulley on the seconds arbour.
• a 60t pulley on the auto-winding motor would mean 60x60/18s = 200s per rotation of motor shaft <tick>
• 18t timing pulley is only about 12mm OD. 
• 36t at 24mm would be better giving 100s rotation rate for the motor
• a 36t timing pulley could be 3D printed

One "push pallet" added.

Yes, the material is plastic - PLA in fact.  But I have built two working clocks with this material that have proved very successful.  This current clock is more demanding and I have found the limitations of the material.  This is why I have abandoned the traditional type of escapement for longcase clocks and gone for a much more tolerant type.

I think I should start a new Blog for the gravity escapement version of the clock.

Changed the arms to take ball bearings and adjusted the dimensions.  Pivots are 150mm above centre of escape wheel (and clock generally).

Error fixed though pallet sizes may not be final.

Now working on the design of the pallets etc. on the arms (Don't know if this is the right name for these parts but...)

This is the result.

Aarrgghh - got things back to front.  Not to worry - easily fixed!

Gradually designing and adding bits.

The gearing between escape wheel pinion and centre wheel can't just be the same as before as the distances are wrong.  One gear pair used 80:10 and the other 75:10 with different spacing of the axles.  Now the spacing has to be the same as the arbours are concentric.  This means using a different modulus on one pair.

Alternative escape wheel with built-in pinion.

This is assembled onto the arbour.

This is how the escape wheel without pinion would go on the minutes arbour with separate pinion other side of panel (not shown), but this would rely on being able to fix escape wheel and pinion tightly onto the arbour/axle.  Tricky!!

The escape wheel will look similar to the deadbeat wheel except that the locking side would be radial rather than at an angle and there will also be pins that will drive the legs outwards.

One version of the escape wheel.  The pins would have to be on a separate part.

Alternatively, the pinion could be separate - indeed even on the other side of the panel.

The arbours, one inside another could look like this for the seconds and minutes with the hours on the outside of the minutes tube.  The seconds arbour/shaft being stainless steel and the minutes being printed PLA.

The next point is that it looks like the escape wheel would have to be situated in the centre of the clock rather than offset and this is what the author of the article has done.  This changes how I could arrange the gears.  I think the escape wheel would have to be on a concentric arbour system as he has used.  The pinion for the escape wheel could be attached to it as now, increasing the space required even more.  It does mean the intermediate gears can go off-centre though.

The gear that mates with the escape pinion would have to be behind the back plate and connect with its pinion by a shaft through the back plate.  This latter pinion would mesh with the center wheel (minute wheel).  The rest of the going train could be similar to the present design.

Drive from the weight and timing belt could be applied to the seconds to minutes intermediate gear as now but would probably need a shaft through the back plate.

I have used 3 concentric arbours before - in my Moon Dial Clock.

I think this is beginning to look feasible.  For testing a working model, when I get that far I think I shall use a simple weight with a string on a drum.

I think I shall do some experiments with the 30-legged gravity escapement.  The first will have to be CAD based.  I think there could be a problem with the number of "levels" involved but have to see.

The escape wheel, legs and pendulum rod could occupy the same space if this were deep enough.  This means the escape wheel would be behind the back plate.  Currently the gap between the back plate and the case is 35mm but could be increased and I think it would need to be.

With the pendulum free swinging, I was able to time 60 swings against the sweep seconds hand on my giant wall clock.  I got 56s so 4s in 60s too fast.  Distance from suspension to centre of bob is 105cm.  I guess the rod is making the CofG higher.  Maybe I want a heavier bob.  As it is I would want to increase the rod length by 4x105/60 = 7cm.