Some locos, such as the
SD-9, were designed to run long hood forward. Even so, some roads
ran them short hood forward. Most roads painted a small "F"
on the front edge of the walk-way to indicate which end of the engine
was considered to be the front. If you look closely, some of our models
have this "F" there. Never-the-less, even if the road ran
the loco one way or the other, some modelers prefer to run it whichever
way they deem to be forward.
Base Direction is a term used to
describe the direction the loco will go when told to go forward and
is also one of the decoder's features that allow you to set and/or
change the Base Direction.
With traditional DC Analog control,
there is no base direction because there is no way to tell the loco
to go forward. Physical direction is controlled by the polarity on
the rails. Whether the loco goes forward or reverse depends on which
way the loco is sitting on those rails. If you give it throttle and
the loco goes the wrong direction, you simply flip the direction switch
to make it go the other way, since there is no base direction control.
With DCC, the loco will go forward
when you set it to go forward and it will go backwards when you tell
it to go backwards - regardless of which way it's facing on the track,
regardless of track polarity, and even going through a reverse section
where the polarity changes beneath the loco.
The loco's Base Direction can be
set and easily changed in several ways. This allows you to run various
locos (such as the SD-9 for example) either long hood or short hood
forward. It also allows for running two locos together, tail-to-tail
or nose-to nose. But mostly, it allows DCC to make the train go forward
when you tell it to go forward - regardless of where it is on the
layout and which way it's facing on the track.
The Base Direction feature is just
one of several ways to control a loco's direction. Other ways include
CV19 (Decoder-Assisted
Consisting), wiring the motor backwards, and direction control
on the hand-held throttle. We'll discuss all this below.
1) Most decoders provide Base-Direction
Programming. This is bit zero in CV 29 (more about this later). Decoders
with this feature come with bit zero cleared - for forward direction.
By setting bit zero, the base direction of travel will reverse - that
is, when told to go forward it will go backward. There are reasons
one might want to use this:
First, Base Direction is handy if
your system doesn't support MU consisting and you want one loco in
the consist to go backwards (for tail-to-tail consisting) when the
lead loco is told to go forward. Refer to Decoder-Assisted
Consisting for more information about MU Consisting.
Second, some locos were designed
to run long hood forward, such as the SD-9, but some railroads ran
them short hood forward. If you get a loco that is pre-wired for DCC
to run long hood forward, but you want to run it short hood forward,
all you have to do is set the Base Direction bit.
Some people errantly think this can
be used to correct a wiring mistake (they connected the orange and
gray wires to the motor backwards). But if the front and rear lights
are wired correctly, setting the direction bit will also reverse them
to make them wrong. If you make a mistake in decoder wiring, it's
best to correct that mistake.
2) Many decoders have Decoder-Assisted
Consisting. This uses CV19. When an address is programmed into
CV19, bit 7 of that CV dictates loco direction. When bit 7 is clear,
the base direction of the loco is unchanged. If set, the base direction
of the loco is reversed from the direction bit 0 of CV 29 has it
set for.
3) When wiring a decoder, the orange
and gray wires are connected to the motor. The orange wire should
connect to the "+" motor terminal - the one that was connected
directly to the right rail (except for G scale) power pickup lead.
The gray wire should connect to the "-" motor terminal -
the one that was connected directly to the left rail (except for G
scale) power pickup lead. G scale is backwards from all others: left
rail is positive and right rail is negative. Wiring this way will
produce a loco that will go forward when told to go forward and backward
when told to go backward.
4) You have ultimate direction control
of the train with your hand-held throttle. If everything is set up
correctly, the train will go forward when you tell it to go forward
with your throttle. But if for some reason it doesn't, all you have
to do is press the direction button (or flip the direction switch,
whichever your throttle has) and the loco will go the other direction. |
