DCC and gradients

[RichD1]

I'm in the planning stage of a layout. I've not had a layout for almost 25 years so am thinking that DCC is the way to go but as I've got around 60 locos this will have to be a gradual conversion and the wiring will have to be DC compatible.

 

The layout I current have is a round-roundy with a folded figure of 8 and twin tracks. The size of layout will be 3.1m x 3m and the gradients will be a max. of 2% but this will require that there will be gradients on at least three sides and some on curves with at least 600mm rads. I will probably be limited to 4 coach rakes due to the available space for a station.

 

My question is; does DCC offer better torque and constant speed control to cope with the gradients?

 

Richard 

[Frutigen]

I have the same situation on my N gauge layout and I find that my locos give near constant speed up and down 2% gradients, including some tight curves, even with long trains. It's great if you just want to watch the train go by without having to drive it every step of the way. To achieve this I set the load compensation (BEMF Intensity) on each loco's decoder to max. Without this, the train speed would swing from struggling to runaway as it goes up and down hill. This is an extreme setting required by this particular type of layout and I think you might not need it for flatter layouts.

 

This brings a few downsides that I can live with.

• On older, less refined locos the BEMF has to work harder and you get a bit of chatter.
• You can get super-slow running on modern mechanisms, even starting a heavy load on a 2% gradient, but older mechanisms might judder a little at these speeds, especially those without a flywheel.
• Double heading (consisting) requires locos that are closely speed matched at all speed steps, otherwise they each fight to maintain their own speed. To achieve this I time my locos around a known circuit on the layout and adjust maximum speed (CV5) until I get my desired lap time. I then adjust starting speed (CV2) so that the loco starts moving as soon as I move the throttle. After that you need to adjust the Vmid (CV6) to match the rest of your fleet so they have similar speed curves. Finally, set acceleration and deceleration (CVs 3 & 4) to match your other locos - this can take a bit of trial and error as each mechanism has its own natural momentum and friction. Beware that different makes of decoder behave differently so you'll get best matching if you standardise on one make.

I find I can haul up to 15 wagons with one loco, after that I get wheel slip when the train is on a long steep curve and double heading is required. Other limitations on train length are (a) dodgy couplings that can't handle the load and let go and (b) long wheelbase 4 wheel wagons with too little sideways play in the couplings, which tend to get dragged over sideways on sharp curves if they have a long train behind them. Both of these problems can be reduced by placing the offending wagon towards the back of the train where the trailing load is lighter.

 

Happy planning

 

Edited January 30, 2021 by Frutigen
Misleading CV reference removed

[WIMorrison]

The problem with gradients is the slip of the locos due to loss of traction and powering the layout from DCC makes no difference to powering it from DC as the loco will slip irrespective of the power. The solution is to either add more weight to the loco, have traction tyres, reduce the rolling resistance of the train (clean wheels and axle bearings) or reduce the gradient. Also be very careful of gradients on curves as the curve will significantly increase the effect of the gradient e.g. a 3% gradient can easily end up as an effective 5% gradient with a curve present.

 

Be aware of people quoting specific CVs to alter as many are specific to particular decoders. The example quoted #CV58 is valid for Zimo decoders but not for others. The NMRA specified CVs are valid for all decoders but there are only a few of them.

[Andymsa]

One thing I do to assist the tractive effort of a loco is to remove the wagon/ coach weights. This has greatly assisted very long trains going up the helix and coupling failure as I use fleischmann couplings on the wagons. I think  you may be surprised how much weight is removed from a 15 wagon goods train.

[jamespetts]

DCC decoders with back-EMF (most decoders have this in modern times; I have had good experiences with Zimo decoders, all of which have this feature and some of which are excellent value for money) give much more constant speed control on gradients than DC power (aside from the old DC feedback controllers, which were an earlier version of the same thing). Back-EMF will normally be enabled by default on decoders (it is enabled and set to its maximum level by default in Zimo decoders), but you should check this when installing a decoder to be sure. It is probably easier to choose one brand of decoders (Zimo, ESU and Lenz are the well reputed brands) and stick with it for all your locomotives to make it easier to remember how to configure each one.

 

As others have pointed out, back-EMF will not help with wheel-slip situations, but that is a different kind of issue.