Adc 9" timing

[Martin Jackson <mjackson@vcn.bc.ca>]

  Ian hamilton asked:
  
"Anyway , I've heard that one can get better "performance" from this 9"
by rotating the brush holder housing, any thoughts on this....."
  
  Good question Ian. I know one 8" motor performs well at a reasonably 
  high Voltage with 12 deg. advance from neutral. 5 and 7 degrees are 
  mentioned, but the 'exact' logic and quantities of advance are not 
  covered in EV List discussions. Some bits of information and guessing 
  are available.

  1) Neutral is typically set on industrial motors since the customer 
     doesn't necessarily know what direction the motor will turn, may 
     use reverse at 'full power' and is happy with heavy & slow 
     continuous service. I believe that some small advance is optimum at 
     any Voltage-speed.

  2) By the same reasoning, using large advance angles reduces 
     efficiency at low rpm. But, you shouldn't use low rpm if you don't 
     have to. 'Low rpm' is a problem because of heating and best 
     efficiency happens at medium rpm. High rpm gives you power when 
     needed and more cooling. This does need higher Voltage though.
     (Too Low rpm = less than industrial rated speed - say, 30%
      Medium rpm = rated rpm @ rated V, rated load
      High rpm = Speed available with more Voltage)

  2) The limit of 30 V between comm bars (per Lee Hart) is maintained by
     'advance'. I think this alteration turns -off- the active rotor 
     coil before the Voltage difference between supply and back EMF gets 
     too high *. Most operation is at much lower Voltage than battery 
     supply since motor current limit in the controller provides reduced 
     Volts.

  4) It is commonly thought that motor current limit (in the controller)
     determines the safe Voltage level because the current in the motor
     sets the Voltage difference between supply and back EMF.

  The vendor of your motor should have a handle on both the advance you
  should be using and the size controller that works with that motor.
  Getting a specific recommendation can be tough because each 
  manufacturer competes to provide the least information and if you home
  build an EV, chances are good you will abuse the motor somehow. The
  warrantee on your motor is limited by the guy you buy it from.

  * I hope there are enough 'facts' in this note to get some real motor 
  experts to comment. Andre Blanchard did the geometry for you.
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