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Gina

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Blog Comments posted by Gina


  1. 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.


  2. 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.


  3. 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.


  4. 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.

     


  5. 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.


  6. 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.

    1734231671_Screenshotfrom2018-10-2919-58-02.png.5ec784d028fa9dc9498d506fdfc8d246.png433655012_Screenshotfrom2018-10-2920-04-14.png.c2af4e6b936ffbac0ff3efcfa9a37327.png

     


  7. 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


  8. 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!


  9. 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

     


  10. I've decided to drive the pendulum rod just below the clock face.  This will consist of a cross-bar connecting rod connected to an offset (crank) bearing on a 64t gear.  A stepper motor will drive this with a 25t gear arranged to drive the pendulum at 2s per cycle.  The electronics will consist of a Real Time Clock module (extremely accurate) driving a TMC2100 stepper driver module.  The latter can provide very quite stepper motor operation (I'm Using one in my Giant 3D Printed Wall Clock).

    • Pulse rate from RTC = 4096 Hz square wave
    • NEMA14 stepper motor has 200 full steps per revolution
    • Microstepping multiplies this by 16x
    • Gear ratio to crank is 25:64 step down.
    • --- Now to the calculation ---
    • 4096/16 = 256.  Equivalent of 256 full steps per second.
    • Seconds per revolution of motor shaft = 200/256.
    • Seconds per revolution of crank = 200/256 x 64/25 = 200/25 x 64/256 = 8x64/256 = 2

    Here's a quote from an earlier post with an Arduino sketch.  I can modify this and drive the TMC2100 directly from the RTC module cutting out a number of lines of code.  The Arduino would only be needed to set the parameters in the RTC module.

    On 29/07/2017 at 21:20, Gina said:

    Here's the new Arduino sketch :-

    
    // Filename :- Pendulum_Clock_v4_with_NEMA14_Auto-winding_2017_07_29
    // Software timing from RTC on pin 2 using polling
    //
    #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_v4_with_NEMA14_Auto-winding_29_07_2017";
    boolean lastSqWave = 0; 
    boolean ledON = 0; 
    int count = 0;  // Used to flash LED
    int sqwPin = A6;
    int dirPin = 8;  // DIRECTION pin
    int stepPin = 9; // STEP pin
    int ms1Pin = 11;  // Microstepping pin
    int ms2Pin = 10;  // Microstepping pin
    int ms3Pin = 12;  // Microstepping pin
    int ledPin = 13;  // Internal LED pin
    //
    void setup() {
      Serial.begin (9600);     // Enable Serial Monitor via USB
      pinMode(dirPin, OUTPUT);
      pinMode(stepPin, OUTPUT);
      pinMode(ms1Pin, OUTPUT);
      pinMode(ms2Pin, OUTPUT);
      pinMode(ms3Pin, OUTPUT);
      pinMode(ledPin, OUTPUT);
      digitalWrite(ms1Pin, 1);  //  16x micro-step mode
      digitalWrite(ms2Pin, 1);  //  16x micro-step mode
      digitalWrite(ms3Pin, 1);  //  16x micro-step mode
      digitalWrite(dirPin, 1);
      pinMode(sqwPin,INPUT_PULLUP);   //  RTC timing pin
      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_1024_HZ);    // 1024Hz square wave            
    }
    //
    void runClock(void){
      digitalWrite(stepPin, 1);
      delayMicroseconds(5);     // Make STEP pulse at least 5μs long
      digitalWrite(stepPin, 0);
      count ++ ; // increment count
      if (count > 512) {count = 0; ledON = !ledON; digitalWrite(ledPin, ledON); }  //  
    }
    //
    void loop(){
      boolean val = ((analogRead(sqwPin) > 500));  // read logic level of 1Hz square wave
      if (val != lastSqWave)  { lastSqWave = val; if (val) runClock(); }  //  Call runClock on rising edge of RTC square wave
    }
    // End

     


  11. Having another look at this project.  The impasse ATM is the escapement.  To date I have not been able to produce an accurate enough escape wheel.  I've worked out that the tolerance required is of the order of 0.1mm and have found this difficult to achieve in a 3D printer.  I may have another attempt with my latest 3D printer.  The problem is that if the teeth are not all exactly the same distance from the centre of rotation and the same shape, the drive is either insufficient to keep the pendulum swinging or the escapement "skips".

    One "fudge" I've thought of is to drive the pendulum separately so that the escapement is not required to drive it.  This would mean a far lighter weight would be needed to run the gear train with less tendency to "skip".  Of course, the pendulum would need to be "tuned" fairly accurately to the 2s period of the drive or the two would "fight".  Effectively, the pendulum is a very high Q tuned circuit, albeit a mechanical one.  Apart from getting round the escapement problem, the clock would effectively be a "slave" to the RTC module and stepper motor driver circuit.  I had planned to add an automatic time-keeping system whereby the pendulum length was adjusted to make the clock keep time.  A closed loop control system.  The open loop pendulum drive would be simpler.

    I want to get the time-piece part of the clock working so that I can get on with the striking mechanism which intrigues me.

     


  12. Drat changing the clocks - it's upset my Moon Dial Clock.  I have a switch on the top which determines GMT or BST and when operated restarts the clock as well as determining whether to add an hour for BST.  Flipped it this morning for the clock change and the hands sensors are not working.  Have to switch it off and make sure the hands are as close to the face as possible.  As I said above, this could do with a design change to make it more reliable.

    The position of the hands is detected by small magnets in the ends of the hands and Hall devices built into the clock face.  I was thinking the minutes shaft went through to the back of the clock but it doesn't - its the seconds shaft - the minutes is a sleeve like the hours but longer.  The sleeves only go back as far as the relevant wheel/gear.  All this seemed a good idea at the time and avoids the standard clock slipping clutch which is the standard way of setting the time and seemed difficult to implement in a plastic geared clock.  Also, the ability to set the time automatically was a nice extra.

    I really don't want to completely redesign and rebuild this clock.  Maybe see if I can use bigger magnets.


  13. The lights dim when I run the mains heater on my Giant printer 🤣  Well, not quite but it is 1.2KW which is more than a bar of an electric fire. 

    Having tried PEI sheet on my Concorde printer with unsatisfactory results, I'm now not sure about using it on the bed of my Giant printer.  I didn't do very well with plain aluminium for print adhesion though and unless I can adjust print settings to make plain aluminium work I shall definitely try the PEI.

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