Gina

Here is a photo of the printer I've just taken.

The thermistor is part of the heater pad.  Anyway, the bed surface temperature is very uneven so I think the heater is on it's way out so I've ordered a good quality (Keenovo) heater pad for about £56 due to arrive on a slow boat from China sometime next month.  Meanwhile, I've increased the bed temperature to a nominal 140°C.  Bed is reading around 90°C to 100°C in the area in which I'm printing.

Print seem to be going alright with the increased bed temperature.

A check with an IR thermometer has shown that the bed surface temperature varies quite a lot over the area.  Also, the thermistor is reading over 20°C higher than the bed surface.  With the thermistor reading 120°C the bed reads from around 80°C to 102°C.  Maybe a new heater and borosilicate glass plate are indicated.  It's a mains voltage heater and not cheap!  OTOH this could be why the filament id not sticking to the bed.

This printer has been working well until just recently when I've been having problems with bed adhesion.  I need to take and post an up-to-date picture as I have added parts cooling, filament feed and support for the umbilical cable bungle plus some tidying up.

I've just given the bed a service.  Cleaned the glass, taken the bed unit apart and checked the brackets etc.  Then I adjusted the Z drives to get the bed as level as possible as I believe the auto-levelling works better if the bed is reasonably level to start with.  I adjusted the LH drive by a few tenths of a mm to give the best levelling as indicated by the results of the Mesh Grid Compensation.  The borosilicate glass plate is not flat but I've reduced the maximum error.  Here are the Automatic Calibration Results top view.

New assembly model.

Changed to mod 3 for the motor drive to the epicyclic gears and it fits nicely.

Here is a new model of the clock assembly.  The modulus of the driving gears (green and blue) has been increased to 2.75 but I think 3 would be better.  The epicyclic gears are mod 2.5.  I'm showing the latest gears as solid until I am sure it's the final design, then I'll add spokes.

Latest design :- 

1. Motor gear with 25t driving the epicyclic system gear if 64t mod 2.5.  Gear is 163mm OD.
2. Epicyclic gears will be 49t fixed and 50t driving the 6t auto-winding sprocket with 8t pinion mounted on the 64t gear.

The above makes the biggest gear 160mm OD.  This would make the drive gear more than mod 2.5.  So now trying epicyclic ratio of 40.

1. Overall ratio required = 128:1
2. If the epicyclic gear ratio were 40 the epicyclic drive gear could be 80t say.
3. Motor gear ratio would be 80:25.
4. Total ratio would be 40x80/25 = 128 [tick]

Later...  No joy with that.  The 80t gear would be 200mm OD and that's too big.

With a 25t gear on the motor it should be possible to use a 50:1 reduction in the epicyclic gearing.

1. Overall ratio required = 128:1
2. If the epicyclic gear ratio were 50 the epicyclic drive gear could be 64t say.
3. Motor gear ratio would be 64:25.
4. Total ratio would be 50x64/25 = 128 [tick]

Now to see how big the epicyclic drive gear is with mod 2.5.

It would be nice if I could use the 25t gear on the motor that drives the pendulum to drive the auto-winding as well but a 4:1 ratio would mean a 100t gear to match which would be far too large.  A 50t gear would give only 2:1 and need a 64t gear on the epicyclic drive.  The upshot of this is that a tooth size of mod 3 is too big for an epicyclic gear system in the space available.  It may be possible to juggle modulus with gear ratios to make this possible.  Some of the gears in the clock already are mod 2.5 so this should be feasible for the auto-winding system.

With a 1024Hz square wave from the RTC, the reduction required is 128:1.

The trouble with ratchet wheels is complication - needs ratchet wheel, fixed pawl and driven pawl plus a crank arrangement.  Advantage is it gives a high reduction ratio bur there are other ways of getting a high reduction ratio viz. worm gear and epicyclic gearing.  I don't think a worm gear lends itself to printed plastic. 

The epicyclic gear system as used in my Giant Wall Clock might be an alternative to ratchet wheel.   A 64:1 ratio with 63t and 64 t gears would be rather too large with decent sized teeth but 32:1 should be doable with 31t & 32t gears and mod 3 size teeth.  Dividing 128 by 32 gives 4, an easy gear ratio.

Using the 4096Hz square wave from the clock module wanted a step-down ratio of 512:1.  The ratchet wheel has 64 teeth so that leaves 8:1 ratio.  If I changed to 1024Hz the remaining step-down would only be 2:1.  This would mean the pendulum drive gears would need to be a 25:16 step-up ratio.  Not sure this would be a good idea, though admittedly the load is very light.  There isn't a setting of 2048Hz though this could be simulated in the Arduino sketch.

Another plan...

I think I might put the auto-winding and pendulum pushing stepper motor below the clock face (hood) behind the body door.  I don't think all the auto-winding mechanism needs to be in full view and I think it would make things a lot easier.

On 30/10/2018 at 15:55, Gina said:

Model of clock "works" in case.  The dial isn't really white, it's black but the CAD software adds white lines round everything.

Back plate added to show space available.

Components of the striking mechanism hidden.

CAD assembly model.

The teeth on the 64 tooth ratchet wheel seem rather small with 120mm OD as fits nicely in the clock case so I'll have a rethink.  Could use 32 teeth and 4:1 motor to crank wheel.

The 125mm ratchet wheel might work with a gear on the 8t sprocket with 50 teeth or more.  Need to do some calculating do see if this would be viable.

1. 8t sprocket want to rotate at 400s/rev.
2. Motor shaft rotates at 200/256s/rev = 400/512s/rev
3. This makes total reduction required 512:1

This is purely a power of two so ratios of 5:1 are out it seems.  No problem, just need to design and print new ratchet wheel and gears.  I think this can be achieved with a spur gear on the 8t sprocket and matching ratchet wheel pinion.  8:1 gear ratio and 64 tooth ratchet wheel.  This assumes the pawl works directly off the motor shaft but a 2:1 reduction gear would make the sprocket to ratchet wheel ratio a more manageable 4:1

I have some ratchet wheels from previous versions with 50 ratchet teeth and 10 tooth pinion.  Smallest is 125mm OD which is a bit big.

Here's a photo of the current state of the clock.  To get an idea of scale the chain wheel is 125mm OD.

On 25/05/2019 at 14:51, Gina said:

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...

1. The centre wheel turns once per hour so the drive sprocket 4 times an hour or 15m per revolution.
2. Chain drive sprocket has 18 teeth and motor sprocket 8 teeth.
3. 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
4. I expect to use a NEMA17 or maybe NEMA14 stepper motor with 200 steps/rev.
5. If I were to use 1 step/sec motor speed the motor shaft would rotate at 200 secs/rev
6. 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. 

If I were to use the same stepper motor for the auto-winding as the pendulum drive the above will need modifying, viz.

1. The centre wheel turns once per hour so the drive sprocket 4 times an hour or 15m per revolution.
2. Chain drive sprocket has 18 teeth and motor sprocket 8 teeth.
3. 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
4. The crank gear runs at 2s per rev so the drive would want reducing by 200:1.

Seems this calls for a ratchet drive system like I used before.  Not a 200 toothed wheel though!

It would be helpful if I can drive the auto-winding from the same motor so the next thing is to look at the calculations.

This is all that's now required in the sketch and in fact, I don't think it needs either the Serial Monitor  or to get the time from the RTC module.  I shall try it without and leave just the square wave setting.

// Filename :- Pendulum_Clock__v5_with_NEMA14_Auto-winding_29_10_2019
//
#include <DS3232RTC.h>    //http://github.com/JChristensen/DS3232RTC
#include <Time.h>         //http://www.arduino.cc/playground/Code/Time  
#include <Wire.h>         //http://arduino.cc/en/Reference/Wire (included with Arduino IDE)
//
String VerString = " Pendulum_Clock_v5_with_NEMA14_Auto-winding_29_10_2019";
//
void setup() {
  Serial.begin (9600);     // Enable Serial Monitor via USB
  Serial.println(VerString);
  setSyncProvider(RTC.get);  // the function to get the time from the RTC
  if(timeStatus() != timeSet) 
      Serial.println(" Unable to sync with the RTC");
  else
      Serial.println(" RTC has set the system time");
  RTC.squareWave(SQWAVE_4096_HZ);    // 4096Hz square wave            
}
// End