Well,
to my knowledge there is no guarrantee whatsoever about default driving direction. There was i discussion a long time ago where I learnt that even field coils may be winded in different direction. So I guess you'll have to decide yourself how you want it and adjust it accordingly.
German electric locos have a '1' in the A-end, and I think there is slight precedence of having the slider forward. But i've had it the opposite way around in a few cases, where I want to shorten the distance between locos slider and cars slider (due to circuit tracks aspects).

It's true that modern decoders remember direction. But you might also encounter another problem. If I've got it correctly, many decoders have a state to indicate wheter they are running the "right" diretion or not. If such a loco goes from an analogue section to a digital, it continues regardless of the arrow setting of the control unit; it would be very bad if it should just begin to go the opposite direction. I don't know how to make sure that this state is reset.
/Lars

Their convention is the pickup slider is pointing to the forward
direction. This might not be applied consistently but the overwhelming majority of B and C truck locos is following it.



That`s a characteristic of older/Motorola 1 decoders.
If you turn off power whilst the loco is not selected to run in the default/"preferred" direction, it will switch to its default direction
as soon as the decoder loses its memory.

How long is that? Depending on the badge of decoders, that`s about
two minutes to a couple of weeks.

Hence the recommendation in older signal books and k84 decoders manuals to install a resistor between the two poles turning off/on power in signal block sections. The resistor will let pass a small amount of power, enough to support the decoder`s memory, but not powerful enough to move a loco. Lighted cars standing with their slider shoe in the same block section will reduce the power to a level not high enough to support the memory of the decoder.

Regards,
Manfred

All modern locos and all modern control equipment, i.e. equipment that uses either the "new Märklin/Motorola" format or the "mfx" format, have "absolute" direction control. This means that for the same loco, a certain driving direction on the control unit will always result in the same driving direction for the loco. The "default" can be different between different locos, but should not be different from time to time with the same loco.

For older locos this is not true since they have only "relative" direction control. Also older control equipment, or equipment configured to send only old code formats, may send only relative direction commands. A digital loco may also remember the last direction driven and start with that direction if it is placed on an analog layout.

Hi

In some leaflets that come with the locos it is written that the loco has a preferred direction of travel with respect to the slider position (I mean electical and diesel, of course). Why is this important? Does it have to do with what it has been discussed here?

Cheers,

Nuno

Yes, and that is rather annoying. If you turn off the power to the 6021 while trains are running, and then turn on the power to it again after a while, some trains may remember their speed and direction and drive away in the previous direction.

I find it strange that Märklin haven't thought of this situation. The 6021 sends out an "idle" message after power up. The natural way to interpret the "idle" message would have been to see it as a general "stop" message. But instead, the decoders interpret it as a stop command to address 0 (which isn't selectable on the 6021 but can be used in a loco if you have a control equipment that can send commands to it).


If this situation arises, you just push "stop". Then you can set each loco to its desired starting condition without being in a hurry.