The PID in the Xylotex.hal file is to eliminate 'hunting' by the low 
level stepper code that runs in background to maintain position (sort of 
like a servo).  While the position is actually stable and no STEP pulse is 
actually generated, the DIR line can end up toggling.  This can cause noise 
on stepper motors via the stepper drives changing current level to the 
motors (probably actually changing the decay mode for coil 
charge/discharge).  Not all stepper drive suffer from this problem, so this 
change isn't needed for all systems.  Nevertheless, the changing current 
level from an affected drive can cause an audible noise from the motors. 
Removing the hunting removes the DIR change thus removing the additional 
noise on the motor.


On Wednesday, November 30, 2016 at 7:35:36 PM UTC-8, Mike Ross wrote:
> I have the toolchanger working as intended!  I will post the revised files 
> later after I have tuned up the axes for the correct steps per move etc. 
> but I thought I'd post the rough solution for those interested.
> After much studying of the code of hal file, the ini and the 
> toolchanger.comp I was almost ready to take up coding a new 
> toolchanger.comp that was much simplified (because I can't really write C), 
> but then I had another thought.
> On comparing the Xylotex.ini and Xylotex.hal with any of the other hal and 
> ini for other BBB capes (CRAMPS, Probotix, BeBoPr, etc) I thought I'd try 
> and get rid of the PID function on the stepper motors as only the Xylotex 
> config has it and the others seem to work fine without PID on the stepgen.  
> That was the fix.  
> After that I was able to make and break all the right connections and now 
> the toolchanger will cycle through the 6 positions and back up after it has 
> arrived at the final position (and I still have my X and  Z axis working).
> Thanks again for all the help along the way.
> Mike

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