These three CVs allows
you to modify the built-in speed curve enough to match dissimilar
locos, and enough for almost any other need you'll have. Without them,
you must use the User-Loadable Speed Table
to create a custom speed curve. Considering that the User-Loadable
Speed Table is about 8 times more cumbersome and complicated, most
people don't want to tackle it. But most people can easily understand
and implement these three simple CVs.
V-Start (CV2) allows you to tell
the decoder how much voltage to provide at speed step 1. This allows
you to program it so the loco will crawl on the first speed step.
The value you program into this CV is relative only to the percentage
of voltage available to the decoder. For example, a value of "01"
provides 1/255th of the available voltage while "02" provides
2/255ths of the available voltage. Since the G-scale setting provides
more voltage on the track than N scale, this means that any given
value will provide more voltage in G scale than it will in N scale.
Basically all this means is that
the higher the value you place in CV2, the more voltage will be provided
at speed step 1. If your loco doesn't run on speed step 1, it needs
a higher value. If it runs too fast on speed step 1, CV2 needs a lower
value. Regardless of the value used for speed step 1, all other speed
steps above #1 will be stretched up proportionately to make a smooth
ramp all the way up.
V-Max (CV5) allows you to set the
maximum voltage the loco will get when on the highest throttle setting.
This allows you to set the loco's maximum speed at full throttle.
The default value of zero ("00") disables this CV, providing
full voltage at full throttle. Values above zero work similarly to
V-Start (CV2) - the higher the value, the faster the loco will go
at full throttle. Obviously, if the loco won't go fast enough at
full throttle with this CV disabled, the highest setting can't make
it go faster than it can go. Regardless of the value used for the
top speed step, all other speed steps below that will be stretched
proportionately to make a smooth ramp all the way down.
V-Mid (CV6) allows you to set the
amount of voltage the loco will get when on the middle speed step.
Without this CV, there would be no speed curve - just a straight ramp
from the value in CV2 to the value in CV5. With CV6, you can make
a curve to suit your needs. Most people make a low-belly curve. This
provides finer speed-step control at the lower speed steps where it's
needed, and a greater increase per speed step at road speeds where
that's needed. Regardless of the value used for the middle speed step,
all other speed steps below and above will be stretched proportionately
to make a smooth ramp from speed step 1 to the middle, and from the
middle to the top speed step.
Note: V-Mid may not work (depending
on the decoder) unless CV5 is set with a value greater than zero.
For years, only V-Start was implemented,
usually for all speed steps . A few years ago, V-Max and V-Mid were
implemented for the 14- and 28-speed-step modes. Only recently have
manufacturers started implementing all three of these CVs for all
three speed-step modes.
Considering that using V-Start, V-Mid,
and V-Max is a very easy way to produce a custom speed curve that
most people will use, and the User-Loadable Speed Table is something
that most people don't want to bother with, I've always wondered why
most decoders have always had the User-Loadable Speed Table, but most
did not have these three simple CVs implemented for the 128-speed-step
mode until just recently. For me, this is an enigma. |
