DC Syndrome (Jim B)
By Jim Betz
When we all learned to run trains - back in the days of DC - we were trained/conditioned to a certain behavior in terms of how we used the throttle ... start turning up the throttle, slowly, until the train starts to move - and then adjust the speed to be what you want. DC cabs "just work that way". Even as the DC cabs got more sophisticated - such as the MRC Tech-II series that used PWM to "lock on to the locomotive" (those words were actually part of the MRC marketing strategy) it became easier. Usually the first point that the loco moved was very close to the right setting for starting a train moving so the "adjust" part of the training I mentioned above was less evident. But the bottom line was that you kept turning up the speed until the train started to move.
But that method does -not- work well for most DCC locos, and especially for any loco that has a decoder with BEMF or is using even modest amounts of momentum ... because most of us "tune" the motor CVs so that if you advance the throttle to speed step 1 - it starts moving. Additionally - most locos are set up with some level of momentum in them ... to "smooth out" how they operate. And also to take advantage of many sound decoders. In fact, for most sound decoders we end up using not just some but -considerable- amounts of momentum ... in order to allow the decoder to "do its thing" with respect to how the sound "loads and unloads" (to simulate what we hear when a real train is accelerating/decelerating). The result is that if you use the "DC Syndrome" approach to starting or stopping a train ... you will over shoot the target speed. And often significantly so! The other side of the equation is that it was a common practice back in the days of DC to do the reverse when you were slowing down ===> just keep turning the speed down until the loco/train is moving at the speed you want it to be running. And again -if the DCC loco has any momentum programmed into it the likelihood that you will over shoot is greatly increased.
- Proto-Typical Locomotive Behavior -
It's really all about "capabilities" and "load" ...
Whether you are a proponent of proto-typical operation of your locos or not ... you will benefit by understanding how real trains behave ... in order to fully understand/relate to the stuff above and apply that to how you run trains. A real loco has a lot of 'delay' between the setting of the throttle and the loco/train reaching the 'steady state' of that setting. This is true whether it is speeding up or slowing down and whether or not it has a heavy train behind it or not or if it is on a grade or not. The engineer controlling the speed of a train is doing stuff that is a lot more like what happens with a ship at sea than it is like what happens when we drive an automobile. A train accelerates slower (takes longer) and also decelerates slower - considerably - than the way an automobile behaves - even when the engineer is using the brakes or dynamics. In addition - every time a real engineer steps into the cab of a different train he has to adjust how he will operate it. Because it will have a different loco/locos (capabilities) and/or a different number of cars behind it (load).
- Putting It All Together -
Operating your DCC locos/trains ...
Either in a prototypical manner -and/or- if the loco has momentum programmed into it ... is essentially the art of: Anticipating what -will- happen ... in the future... and Waiting for it to actually happen.
What that means is that if you are starting a loco/train you need to click just once ... and wait ... and then click the speed up a bit more ... and wait ... until you have the loco moving at the speed you want it move. Similarly, when slowing down ... for something such as a station stop on a passenger train ... we need to start slowing down a lot earlier (further away) ... and then keep making small (tiny?) adjustments until the train reaches the "target speed" - or stops at the intended point.
===> It's really that simple! Try it, you'll like it.
And learning how much delay/momentum there is in this particular loco/train is the "art" of being able to be In Control of this train, now - and the next train, then. Just like the engineer on a real train adjusts what he does based upon the makeup of that particular train. AND - if you find your self "always having to make relatively large adjustments to the speed of the train" - such as slamming the throttle all the way to zero speed ... and then still seeing the train go past where you wanted it to stop ===> then if you say to yourself "I should have started slowing down earlier" rather than "this thing has too much momentum in it" ... you will quickly learn how to operate that particular train (loco) ... and the next one. Luckily, all you have to do is to make small changes to the cab/throttle ... and wait and see what happens. Sounds too easy doesn't it!!!
The hard part is re-learning ... because we all learned to run model trains back in the days of DC. And our DCC trains are almost always considerably different. And when you think about it - that's a good thing.