From ESU LokSound Yahoo Group, Tue Oct 11, 2016
Posted by: Bob Sobol
I
started installing the Loksound L, not XL, decoders in O-scale locomotives
containing Pittman 8000-series motors and have been able to achieve
buttery-smooth operation with excellent low-speed performance. In doing so I
learned a couple of things so far that I hope will help you. I also installed a
LokPilot XL (no sound, but the same motor drive as the Loksound XL) and got it
to perform equally well.
Every attempt with auto tune has resulted in rough operation. Every attempt
produced regulation parameters for CVs 51, 52, 54 and 55 that caused
"surging" (a sudden, temporary increase in speed) or
"bucking" (a sudden, temporary reduction of speed). Manual adjustment
overcame these difficulties.
First principle
If a locomotive suddenly leaps forward, "surging" or
"bucking" it is a sure indication that one or more of the Regulation
parameters is too large. What's happening is the decoder tries too hard to
regulate the speed and it overcorrects.
Basic setup
In my engines I get the best results turning off CV124.4, "Adaptive
regulation frequency" and setting CV10, "Back EMF sampling period"
to its largest value of 8. CV49.1, "DC Motor PWM Frequency" is set to
40 KHz.
CV56, "Regulation influence" was left at maximum, or 255.
By the way, the names of CVs in this post are those found in LokProgrammer, not
necessarily the names defined by the NMRA.
Low speed
For smooth operation in steps 1 and 2, try manually setting CV51 "I
slow" to 0, and CV52 to a small value, much smaller than auto-tune
recommends. Perhaps half or less. So far any nonzero value in CV51 caused my
locomotives to surge every time.
For a Pittman 8414 motor in a P&D/Weaver drive train, with no flywheels,
anything larger than 10 in CV51 caused surging at steps 1 and 2. So to tune
CV52, try reducing it until the bucking stops, then slowly increase the value,
perhaps as little as steps of 2, until you lose smooth operation. Then back
off.
Higher speed
For higher speed steps, if either CV54 "K" or CV55 "I" is
too large then the locomotive will surge. To manually tune, I set CV55 to a
very small value, perhaps 10 or less, then go about setting CV54. If 54 is too
large, the locomotive will surge. If too small, the locomotive slows down too
much as the load increases, such as when running through the curved leg of a
turnout. When satisfied with CV54, then CV55 can be increased a little bit
until surging re-appears, then back off 10-25%.
Adjusting top speed
Much finer control and improved low-speed performance can be achieved by
reducing CV5, "Maximum speed" so that the engine can run no faster
than you desire.
Alternatively, CV53, "Regulation reference" can be reduced. This is
the back-EMF voltage the motor produces when running at full speed. For the
Pittman 8xxx motors I dropped it down to 50, or 5 Volts.
Next I adjusted CV2, "Minimum speed" for the desired starting speed
in step 1.
Momentum
I understand that a lot of modelers do not like or are afraid of running an
engine with momentum. Some momentum is necessary when running in 28 speed step
mode to make a smooth speed changes when adjusting the throttle, even when by
only one step. With considerable momentum, the sound schedules will produce far
more prototypical behavior.
So far this has worked for me. I hope it will work for you.
All the best
Bob
