DCC 28 or DCC 128 ?

[3 link]

Hi Guys,

 

Being a bit of a newbie to DCC, what is the difference between DCC 128 and DCC 28 ? I model in 7mm and am using Touchcab through a Lenz system if that's any help. In the Touchcab app on my iPhone it gives you the option of 128 or 28 ?

 

Martyn.

Edited November 29, 2017 by 3 link

[johnd]

Why would you only want to control your loco's with 28 speed steps when 128 speed steps are available ? Finer control with 128 hence no question to my mind.

[shibushe]

Hi Guys,

 

Being a bit of a newbie to DCC, what is the difference between DCC 128 and DCC 28 ? I model in 7mm and am using Touchcab through a Lenz system if that's any help. In the Touchcab app on my iPhone it gives you the option of 128 or 28 ?

 

Martyn.

Martyn. These are Speed Steps. The higher the number the smoother the acceleration. There is another 14. very course and not recommended.

For instance. At 28 a Loco may move at Step 1. At  128 it may move at Step 5 or more, if you see what I mean.

Or at Step 28 you will reach Maximum throttle quicker.

Edited November 29, 2017 by shibushe

[Sir TophamHatt]

If I'm running a passenger train, 28 steps. If shunting, 128 steps.

[Phil S]

An alterative thought: based on information provided by LGB with their decoders - which originated back in the days when ONLY 14 speed steps were available....  BASED on using a KNOB/Slider speed change !

 

LGB decoders were considered relatively advanced, over 10 years ago, being designed and programmed to cope with the garden environment.

 

And how may speed steps does a diesel or electric loco have in the full size reality??

 

The red LGB handsets only offered 14 speed step control - which is overidden by adding a massoth handset into an MTS 3 central cotroller.  from the beginning, such as zero-1, 14 speed steps was the standard.   However, for smoother speed changes, the LGB decoders INTERNALLY used 1024 steps .... and interpolated between the commanded 14 steps ..... giving a smooth transition between 'running notches'.   They also included a memory to ensure continued running if dirt on the track caused a loos of control informaion.

 

A very obvious technical difference between the 14 speed steps and the 28/128 steps later option, is the control of directional lighting - which shows up as the lights going on and off as the speed changes ... because 1 bit of the original 14 bit speed byte was used for the lighting info .... but then became part of he speed information.` 

 

But back to the reality of 28 or 128 speed steps ..... given acceleration and deceleration values in CV3 and 4 controllng how a loco changes from 1 commanded speed to another, if they are not '0' (implying instant) and especially if the loco has a flywheel,then I would be hard pressed to observe the difference in normal operaton between 28 and 128 steps .... your knob controller may not even digitise it to more than 28 levels !    

 

If running timed loops or under computerised control (such as RR&Co) which literally learns a loco's speed profile over a known distance by repeated run-throughs, then  the differences may show though ... partly because, the inertia appears to 'taken over' by thecomputer - which, in my experience, was in conflict with sound locos which tended to have heavy settings of inertia to match the sound picture.  

 

Finer adjustment for shunting is commonly available on an F button to rescale = in whch whichever  of 14 28 or 128 are respread across a smaler output speed range ....  with the cv3 and 4 acceleration values overiidden for the purpose.

 

SO it probably depends more on the internal software of your chosen decoders, and their V 3, 4 , 5 and shunt settings than any 28/128 being manually controlled 'hands on'.

 

(There have been 'other' speed options such as '27 steps which was really 14 speed steps hoppng back anf forth to effectively give a half-value .. again a software interpretation dependant on the decoder.

 

If, as suggested earlier, the acceleration rate is changed 8x or 4x by changing betwen 14 and 28 and 128  (   14[16]  > 28[32] > 56[64] > 112[128]  - that would be poor programming, in my view !    But I have not reverse engineered any decoder software 8-)  UNLESS USING PUSH BUTTON - where every single speed step haviing to be pressed would be tedious !!  (   if holding the button casues a ramp in the speed change - then it is affected by the controler's ramp/button response )

Edited November 29, 2017 by Phil S

[Alcanman]

Whilst the obvious answer is -' use 128 steps for smoother control' and certainly this is what I use for for Hornby and Bachmann diesels. Also my US Atlas and Diesels.

 

However, when I purchased a couple of Roco diesels fitted with Zimo sound decoders I found they ran far too slowly on 128 steps and reverted to 28 steps!

[34theletterbetweenB&D]

If you use large values in CV's 3 and 4, you won't notice the difference in movement between 28 and 128, as the transitions between steps on 28 are smooth and extended, far better than those that drive directly by speed step change typically achieve. Since trains typically run to line speed limits in 10mph increments, 28 steps can get you to the 250mph mark (mechanism permitting) if the first couple are reserved for 'creep' and dead slow, good enough for modelling anywhere I would suggest.

Edited November 29, 2017 by 34theletterbetweenB&D

[3 link]

Why would you only want to control your loco's with 28 speed steps when 128 speed steps are available ? Finer control with 128 hence no question to my mind.

Johnd,

 

If you read my post above I did explain that I'm new to all this.

 

 

Hi Guys,

 

Thanks for all the explanations and advice, more simple than I first thought.

 

All the best,

 

Martyn.

[Junctionmad]

if the decoder has acceleration and declaration CVs set, then the number of speed steps is largely irrelevant, I often jump in steps of 4 on the NCE.  IN real time many locos had 8 steps !!

[SRman]

Mostly, 128 speed steps give finer control (as has been said already), and this is also somewhat overridden by having inertia and momentum set high (CVs 3 and 4).

Most modern mechanisms seem smoother with the 128 steps, but I have found that my Underground sets with two Black Beetle motor bogies in each (three units with the same set up) all seem to be more responsive with only 28 steps set. Since the real units tended to only have three or four notches on their controllers, this ties in well for realistic driving anyway.

[johnd]

Martyn good morning.

I wasn't forgetting that you are new to DCC control but was pointing out that for every increase of 1 speed step in a decoder set to 28 speed steps it would take approx. the equivalent of 5 on a decoder set to 128 to achieve providing the other CVs relevant to acceleration are set as standard. 

 

I wasn't going to mention those as you will find out about them as you get more familiar with DCC control.

 

All I can say is if you keep a record as you go along changing CVs if some thing happens you are not happy with you have a record and can always take a backward step to your previous settings  without going back to the original settings ( usually by setting CV 8 to 8, but be aware that may not always be the case.) 

 

Just as a general point if you decide to use a number of different decoders I find it useful to keep the instructions supplied with each decoder where I store the loco either the box or in a file nearby.

 

I was in your position of being new to DCC a few years back as all of us were and was trying to give you a simple answer to  your question. You will learn about it and it will become natural to you all I will say is enjoy the benefits of controlling the Locos  and not the track and please continue to ask question.

 

John

ps. a relevant good book on DCC is useful.

[shibushe]

Martyn. Your a learner like most of us at some time or other when we dip our toes into what could be a digital minefield.

Just start with the basics, don't get bogged down with all the tech stuff that will come later.

One tip that I would suggest.

When playing around with CVs write down what you have set a particular CV to against the Loco you are programming easy to forget what the last one was.

[Sir TophamHatt]

^ that's a good tip.  Especially when testing.

 

Currently, my skill level is treating DCC like DC.  I stick the train on the track, select it and then turn the knob.

 

Until my layout is built and I've run in a few trains (naughty converting them to DCC without running in, I know!), I'm not even bothering with adjustments like speed steps and this and that.

[3 link]

Thanks for all the help guys, sorry for the late reply, too much work and not enough play.

 

I will certainly take on board all the advice especially the tip regarding writing down each time you change a cv , as my memory is terrible.

 

All the best Guys,

 

Martyn.

[Junctionmad]

^ that's a good tip. Especially when testing.

 

Currently, my skill level is treating DCC like DC. I stick the train on the track, select it and then turn the knob.

 

Until my layout is built and I've run in a few trains (naughty converting them to DCC without running in, I know!), I'm not even bothering with adjustments like speed steps and this and that.

Running in under DC before DCC is completely superfluous, run them in under dcc. Edited December 6, 2017 by Junctionmad

[Oldddudders]

Running in under DC before DCC is completely superfluous, run them in under dcc.

 

Yes, it is idiotic of manufacturers to suggest this, when most people who run DCC probably got rid of the DC powerpack. But it lets the manufacturer off some sort of hook if the loco ran sweetly under DC yet is a pig under DCC. The diagnostics are more confused if the DC stage is missed. 

 

I will typically run a loco back and forth on Address 0 before installing a decoder, to check basic motion, but by no means is it exposed to DCC enough to be run-in before receiving the decoder. 

[coachmann]

I want my locos to behave realistically especially when pulling away from a halt, so I use 128 speed steps with acceleration controlled with a dial rather than letting the chip control acceleration with CV3 set to a high value.  CV4 is a different kettle of fish and I set it to high values so that trains can be brought to a stand using F'key#2 active brake (with the brake reduced in aggressiveness vie the relevant CV).

 

Vee all haff our own vays.