From: default@defaulter.net   
      
   On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound    
   wrote:   
      
   >Am thinking about building an electronic sextant that would provide near   
   >centimeter accuracy.  This would mean a degree should be partitioned to   
   >about 400,000 steps.  Was considering using a pot and 5v to feed an A/D   
   >but on reflection think that a single turn pot would not be clean enough   
   >for that many steps.  Would someone confirm this for me.  Use of a   
   >multi-turn pot requires gears which would be too expensive due to their   
   >very critical meshing needed.  Thanx, Ron   
      
   Use an optical encoder to provide a pulse train - that's going to cost   
   too   
      
   Gears don't need to mesh perfectly - they can be "anti-backlash"   
   styles.  Look them up.  A pair of identical diameter gears on the same   
   hub both engage the pinion gear and are pushed apart slightly with a   
   spring - ensuring that there is zero backlash - one gear face on each   
   gear is engaging the pinion gear at all times.  They were used in gear   
   tuning systems in communications receivers.   
      
   One assumes you want to be looking through the eyepiece while this   
   counter thingee reads the angle off the sextant?   
      
   Perhaps the trick would be to take an off the shelf digital micrometer   
   or caliper (very cheap with high accuracy) and somehow work that into   
   the sextant scale.   
      
      
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