Some old notes

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I was browsing around some of my files on the clock and figured I'd post some of the notes I took on the drive components.  From my notes on 3/16/2011:


Servos/motors:
I thought about using stepper motors to drive the hands but gave up because the Arduino motor shield can only drive 3 steppers.  I need 5.  This is the model of sail winch servo I used:  GWS Sail Winch Servo S125-1T.  Most places have them for $20-30 each.


After the fact, I think that steppers would be possible with the Arduino using some custom mux/demux circuits to select one of the multiple steppers to drive and an external driver board like this one:  http://www.sparkfun.com/products/10267


The mux/demux circuit could use this chip:  http://search.digikey.com/us/en/products/HEF4051BP,652/568-1689-5-ND/763293




Gears:
I used these two types of gears:  A 1T 2-Y32048 from https://sdp-si.com/index.asp

drive gear on servo:  48 pitch, 96 teeth, 2" pitch dia
hand shaft gear:  48 pitch, 72 teeth, 1.5" pitch dia

For the concentric hand shaft, the brass tubes nest nicely, but to interface with the 1/4" gear hole I will have to increase the diameter of the smaller shafts to fit.  I can cut small pieces of the larger shafts and glue them together.  The tight fit of the nest shafts should work nicely.




Servo positioning:
The Arduino servo class allows controls of 0 to 180 degrees.  Starting with 90 at the 12 o'clock position, 0 and 180 are approx 3 and 9 o'clock positions anti-clockwise and clockwise, respectively.

10 degrees in the Servo library equates to 30 degrees on the clock or one out of 12 positions.  The full 360-degree range on the clock translates to 30-150 degrees in the servo library.  It's pretty accurate but may need some fine-tuning per servo.

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