Very poor acceleration under DCC control

[Chrissaf]

I should add that I have written 0 to CV8 to reset.

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You write 8 to CV8 not zero to perform a factory reset.

[Chrissaf]

I bought a second hand GWR 0-6-0 PT with factory fitted DCC. At first it would not move at all. As I did not know the number assigned to it I wrote no 1 as the address using an Elite controller. Even with this address the motor refused to turn over.

I removed the cover, cleaned the wheels (both track and rear) and the contacts using IPA (not beer, isopropyl alcohol). I also moved the engine and cleaned the plastic worm and the cog.

The engine was still reluctant to rotate but after a lot of fiddling I got everything moving, but very slowly. It took about three minutes to go round an oval track length about 8 metres, accelerating very very slowly. After a further 10 circuits it got up to a fairly decent pace. It slowed down quickly enough, but acceleration from a stop took exactly the same number of circuits. I left it running in circles for 15 minutes and it continued at the same speed.Slowing it to a stop (over two metres ie normal) and then reversing led to the same acceleration characterisitics.

I should add that I have written 0 to CV8 to reset, and read the acceleration on CV3 which I have tried setting to different numbers to no effect.

Using the same programming track, and the same Elite i can program another factory fitted loco with no problems. Any ideas?

 

 

[96RAF]

It sounds like CVs3 and 4 are set to high values, try value 5 if the reset doesn’t cure the problem. You can alter accel and decell on the main using Operate Mode from your Elite Menu button.

Rob

[Fishmanoz]

When you say you’ve written to CV3 to no effect, do you mean you couldn’t write different values or that different values had no effect on acceleration?

[david_nicol]

Thanks to everyone. First I did also write 8 to CV8, after I found out 0 was wrong, with no effect (no effect meaning nothing changed in the behaviour, I have no idea if the actual value changed, I haven't graduated to reading CV's in the the Elite manual because it starts two pages after writing on a programming track and writing on the main track),but I know it had no effect as the control number of the loco which I had set to 1 did not return to 3. I programmed 3 in succesfully by writing 3 to CV3 and then 1 vice versa a few times, showing that at least I could change the loco number to and fro.

Finally I changed the startup voltage using the Elite  system (ie I did not try to find the CV but simply used the Loco->Direct->Address>Startup Voltage menu) and set it to 255. Voila. I am not sure what the startup voltage was set to and it wasn't clear to me whether 0 or 255 meant that the maximum voltage would be supplied to the engine, but now I know! What I do not know is what to do to reset all of the values since in seems as if sending 8 to CV8 fails, although I can confirm the little red light flashes 6 times(see below) .

As a matter of interest the little red light on my Elite flashes 6 times after changing CV, even though it says 5 in my manual, and when I change the loco number it flashes 12 times in two sets of 6!! But it works....

Thanks for all of the other contributors. Finally does anyone know where I can get a simple list of the meanings of all of the CV numbers so that I know which ones to read and write? The Hornby Elite manual only gives a few clues. And I tried to google it but was unsuccesful, probably because I am an idiot.

I might go back to programming computers which is my other hobby, it is a lot easier to write programs in C than to use this stuff.

 

[Rog RJ]

@David_nicol

" I programmed 3 in succesfully by writing 3 to CV3 and then 1 vice versa a few times, showing that at least I could change the loco number to and fro."

 

CV3 isn't to loco address, it's the acceleration rate.  CV1 contains the loco address for 2 digit addresses.

 

[96RAF]

NMRA.org lists all CVs In the DCC section.

Generally on a sliding scale in DCC, 0 is off/stop/etc and 255 is all on/flatout/can’t read it/etc.

Writing value 8 to CV8 correctly on a programming track using Direct programming mode will reset all CVs to their usefull datum values.

Without wishing to be unkind or overly critical and bowing to your own self assessment, you appear to be a random button pusher rather than a user manual reader and follower. In this discipline it pays to read and learn, else despondency can set in and the hobby can be ditched before you have really got into it.

Rob

[Chrissaf]

The reason that you won't find much meaningful documentation about CVs in the Elite controller manual and indeed in any brand of controller manual for that matter. Is because the CVs are specific to the decoder itself. One has to consult the decoder documentation not the controller documentation for all the things that the decoder CVs can do.

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Take a basic Hornby R8249 decoder for example, being basic the number of CVs that are available for adjustment are minimal. The next image below is taken from the R8249 datasheet and demonstrates how minimalistic the CV options are.

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/media/tinymce_upload/9874777cca3ddf6adb15df33f97a2dcf.jpg

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Now take the other extreme of the decoder products, ESU Loksound decoders for example. Look to see in the images below how extensive the range of CVs these high end decoders support. Extract taken from the ESU Loksound V4 downloadable manual.

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/media/tinymce_upload/513442f568f9d7fe0bf6755592cf5b47.jpg

/media/tinymce_upload/55a7690759ee9d4a674ede591d273d38.jpg

/media/tinymce_upload/54e0588f6e9fdb5e359610e1efbbba80.jpg

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Given that based upon reading your post descriptions you don't seem to know what you are doing, we have to then assume that maybe you might not be following the correct CV reading and writing procedures with your Elite controller. After all, unless you video what you are doing and post a link to it on YouTube, we do not have the benefit of looking over your shoulder to see what you are doing.

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Therefore although perhaps a bit harsh, Rob's (RAF96) assessment does seem to have some element of truth to it. You don't seem to have the basics about CVs understood yet. Like for example mixing up the CV3 function with CV1. As other's have said, CV1 is the address CV not CV3. However that said, CV1 is only the address CV for short DCC addresses in the 1 to 127 range. Long [Extended] DCC addresses [128 to 9999] are held in CV17 & CV18 with a flag set in CV29. So as you can see, what you think is a basic CV configuration is not always a straight forward configuration exercise, some understanding of the basic DCC fundamentals are required. Note that most DCC Controllers will have 'user friendly' firmware routines for easily writing DCC long addresses that do not require you to write directly to CV17 & CV18. My mention of CV17 & CV18 was therefore just included for demonstration effect.

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A brand new DCC Decoder should come with a printed sheet that outlines the basic CV functions. However the more high end decoders (like the ESU brand for example and other's like Zimo) usually have downloadable PDF manuals.

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You say you can write Computer programs in C.....if you can do that, then reading a full blown Decoder manual should be child's play to you. If your stated computer background expertise is truthful, then I would expect you to have a good understanding of Binary to Decimal conversion and what an 8 bit byte is. This is a useful skill to have when dealing with some CVs that use 8 bit bytes such as for example CV29 to enable and disable functions.

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So in conclusion and in principle, when dealing with decoders, identify the brand and model of the decoder and download the official manufacturers decoder manual and read that. The controller manual is only needed to document how to physically read and write to the CV. The controller manual cannot go into every CV function because these will vary by decoder brand and model. This is also the reason why you are unlikely to find a generic Internet resource for all CV descriptions, with perhaps the exception of the NMRA DCC protocol standards documentation that cover the mandatory CV implementations, but even then, manufacturers deviate away from some elements of the standard for CVs to suit their own unique purposes. Thus you are much better off referring to the manufacturer decoder documentation when researching a decoders capability.

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For reference and further reading.

The NMRA Standard Index

NMRA S9-2-2 Configuration Variables.

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TIP: I write long posts. If you intend to write a reply, it would be appreciated if you didn't use the 'White Arrow in Blue Box' button. This is not a 'Reply to this post button. It is best to write any reply you want to make in the 'Reply Text Box' at the very bottom of the page and click the Green 'Reply' button.

[Fishmanoz]

You seem to have another confusion in understanding CVs, this time the different between Vstart and Vmax. You say you attempted to set Vstart to 255. Vstart is supposed to be set to the speed step on your controller where the loco first starts to move as you turn your controller throttle up from 0.  It will be a low value like maybe 3 or 5.  Contrast this to Vmax which is the maximum speed step the loco will respond to.  To have it respond to the full range, this is the one you set to 255.

 

But this is all academic as you say the loco has the factory fitted decoder (this makes your loco the one from the Pullman set, running number 2728, am I correct?).  The decoder fitted to this is the Hornby R8249 or 4-pin equivalent, the one Chris has posted the simple CV table for.  As you can see, it doesn’t support CVs for either Vstart or Vmax so you can try to write to these CVs until you are blue in the face and nothing will happen.

 

Your fundamental problem is almost certainly that your CV writing is not working, 8 to CV8 being the immediate case in point.  To fix this, make sure your separate programming track is spotlessly clean, along with the wheels and wheel backs, and that the pickups are clean and tensioned onto the wheel backs.  Now try 8 to CV8 again until it resets the ID to 3, so telling you it has worked. Once you’ve done this, report back and tell us if the acceleration is now normal.  If the loco ID doesn’t change to 3, it means you’ve yet to successfully write 8, not that your decoder doesn’t accept 8.

[david_nicol]

Yes I mixed up CV0 and CV3. Anyway I used the menu system on the Elite rather than the CV which means I actually  did the right thing.

Thanks

[david_nicol]

Well said. Yes, I tend to push buttons and not to RTFM. Manuals are difficult for me to read because I am impatient! I learn better by my mistakes.

Thanks

[96RAF]

Yes I mixed up CV0 and CV3. Anyway I used the menu system on the Elite rather than the CV which means I actually  did the right thing.

Thanks

There is no CV0

[96RAF]

Well said. Yes, I tend to push buttons and not to RTFM. Manuals are difficult for me to read because I am impatient! I learn better by my mistakes.

Thanks

Unfortunately DCC is not an art one can learn without recourse to the many and varied manuals, because what works for one brand of decoder may not work for another as told about by Chris and Fishy.

Rob

[david_nicol]

[snip]

 

Thanks for your very helpful message and a lot of your time. A lot of what you say about me is true. As far as computer programming goes, I started writing in 1969 using Fortran on a mainframe to run an iterative program which modelled the bond energies in a nitrogen containin heterocyclic compound using an early NMR machine at low temperature to compare the computer model with reality. I moved on from that to programming in C after reading Kernigan and Ritchie's book. My first program ran at home on an Amiga 500 and played a very poor game of chess. After looking at the construction of GNU Chess I gave that up, and wrote a lot more for various PC games none of which were spectacular but at least enabled me to understand some more arcane types of higher level languages/query scripts on mainframes in the early 1980's, to give our office access to word processing in a mainframe before PC's became widely available. It wasn't my "proper" job!!

 

My failure to read the manual fully on the Elite is just like my programming, a bit hit and miss but improving from a high error rate at the beginning. In fact I had no intention of learning much about DCC, just enough to get the engine to move.

 

I still don't understand why apparently writing 8 to CV8 didn't reset the startup voltage. However it did reset the value of CV0. Perhaps the value that it had was the default and the default gave very poor acceleration. I did not realise that there was an enormous variation in the way the decoders were set up.

[Chrissaf]

Not having a go, just making an observation.

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It seems to me that reading instructions is not your forte.

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Not just DCC decoder manuals, but forum posts as well. I did ask nicely if you would avoid using the 'blue button' yet you ignored that too.

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PS - There is no such thing as CV0

[2e0dtoeric]

Colour blind, too!  I wonder - if there was a big red button marked Do Not Press, would he press it to find out why?  😛

[Chrissaf]

Talking of which....... a comic story.

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One aspect of my job, when I was working was to do site visits on customer premises, usually requiring a visit to the customers computer / data processing centre.

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On one particular customer site visit. Right next to the electrically operated double doors of the computer / data centre was a great big red emergency button about 3 inches in diameter.

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At my next visit to this particular customer I noticed that the big red button was now encased in a clear perspex case with a padlocked door.

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I think readers can guess where I am heading with this one.

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It transpired that the big red button was the emergency 'power shut down' for the whole computer / data centre and that many visitors who didn't have local knowledge thought it was the door opening button.

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[96RAF]

There is no CV0.

I already said that yesterday....

Our assumption of your reading habits was merely a repetition of your own words, not an assumption of our own.

Rob

[Chrissaf]

There is no CV0.

I already said that yesterday....

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I know you did Rob, it was just that David_nicol reiterated the statement again in the post directly above mine (see yellow highlight below). So I was just re-iterating your reply again to re-enforce the comment.

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/media/tinymce_upload/c149cb24226b34e97a9d77569da79634.jpg

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[96RAF]

I know he did, thats why it was aimed at him.

Rob

[Fishmanoz]

David, returning to your problem, it still seems to me to be that you are having trouble writing anything to the decoder, via menus or directly to a CV.  Could you please re-read my second post in this thread on page 1, particularly the last para.