Complex Speed Curves

[Pendragon Sailing]

As a (relative) newbie to the world of DCC, I’d welcome some wisdom from those experts on this Forum who can explain/suggest what settings I might consider using in setting up the Complex Speed Curves.

I acknowledge there’s a section in the manual which explains the use of these settings, but was wondering if anyone has a suggested ‘starting set’ of CV settings for say a generic Diesel and generic Steam Loco.

Any guidance welcome

Thanks

[WilliamDavid]

So far no replies.

Can anyone explain what the latest update on this is, and what you can manipulate to improve slow speed synchronisation?

[96RAF]

Previously although the complex speed curve CVs existed, the app was not allowing access to them, although they could be amended by direct DCC programming.

What is a speed curve. Now it does.

A simple speed curve is a line drawn between 3-points , starting voltage CV2, mid voltage CV6, and max voltage CV5. This can be a straight line or a bent line and by way of moving the value of the mid point the line can be made to favour improved low end or high end control.

A complex speed curve is enabled in CV29 and consists of very many more points ranging from CV67 to 94. Adjusting these can give better control in any part of the curve, much like a graphic equaliser can give control over various frequencies in an audio scenario.

Anyone familiar with Decoder-Pro in JMRI will have seen the graphic equaliser sliders interface.

What can be done with a complex speed curve. Customised control of a decoder speed to exactly suit your layout operations of any loco but the main advantage here is to adjust the curve on a steam loco which can bring the chuffs sound brackets more into synch with the wheels rotation. Some experimenting has to be done per loco to achieve this but the test team has got a couple of worked examples which I will dig out of the Teams chat pages and repost later.

[WilliamDavid]

Thanks 96RAF

[96RAF]

2/4 cylinder

3 cylinder

[LuLuJo]

Could I just add onto the responses .

Firstly the updated app is great to play around with this so have a go. It was more of a lengthy trial using a dcc controller. The chuff rate disparity of basic profiles is only really observable at low speeds to my aged eyes.

The examples quoted I think came originally from Plomax whose layout was much more shunting orientated. The top speed at 140 is probably around a scale 40 mph depending on the loco so a bit slow for a mainline layout. The results also depend on the engine being used and the sound profile being used.

On my layout which is west coast mainline based I found a higher top end speed was needed.

So I have a standard 4MT mainly used as a banking engine with a similar speed curve as shown above at the bottom end until CV82 then mine steadily increases more rapidly with a final CV of 160. I recon this is about a scale 60mph on this engine.

My 2-6-4T's which have 4F and Black5 sound profiles follow the same bottom end pattern until CV 74 then increase more rapidly to a final CV94 of 195. This is more probably around a scale 80-90mph. This is now my default speed curve. I load this and then adjust to suit the particular locomotive if I am not happy with the results.

The CV's for my base speed curve are the same the previous post then

CV75 23

CV76 27

CV77 30

CV78 35

CV79 40

CV80 45

CV81 50

CV82 56

CV83 63

CV84 70

Cv85 78

CV86 87

CV87 95

CV88 107

CV89 120

CV90 135

CV91 150

CV92 165

CV93 180

CV94 195

Have fun

[WilliamDavid]

Great stuff chaps.

Now let the fun begin.

I love HM7000.

[Britannia Builder]

I've set up the 3 cylinder speed curve from Rob's post above (5, 6 .... 125, 140) for my Peppercorn A1 with the Tornado profile, and it works very well - 6 chuffs per revolution from the slowest to as fast as I can make them out, and a realistic top speed.

I didn't note down the default CV values in the Tornado profile before changing them, but they were nearly twice the above values and the chuffing was way too slow at all but the slowest speed, and the top speed was dangerously high!

I'll try my Bachmann BR Standard 3MT Tank next with the 2/4 cylinder values above, and/or LuLuJo's alternatives.

Regards, John

[WilliamDavid]

Exactly what am I looking for?

6 chuffs per revolution is mentioned above.

How accurately can you get to that?

7 chuffs, 5 chuffs or what.

I've set my V2 to LuLuJo's suggested values, but am not sure what I am supposed to see.

[Britannia Builder]

I would say that my Tornado is making between 5.5 and 6.5 chuffs per revolution at low speeds. I guess that is about as accurate as can be expected without sensor hardware to synchronise the chuffs precisely to the revolutions.

Each cylinder will make two chuffs per revolution, so 4 chuffs for a 2 cylinder and 6 for a 3 cylinder. I believe that 4 cylinder locos such as a Duchess have the cylinders synchronised in pairs, so 4 (double) chuffs per revolution.

Incidentally I had run the auto calibration on my Tornado before setting up the speed curve. I don't know if this would affect the result - ie will auto calibration change the mapping between speed steps and motor speed?

Regards, John

[WilliamDavid]

Comparing my HM7000 fitted V2 with my Bachmann decoder pre fitted V2, the beats per revolution are completely different.

Same with my Howes fitted A3.

Is it possible to get approx six beats with the Hornby A3 profile, or is that too much to expect?

[LuLuJo]

I should have said that my suggested values are for 2 or 4 cylinder engine which as said should have 4 chuffs per revolution. I suggest for a 3 cylinder one which would have 6 chuffs you need the values in the second table in 96RAF post and if you need a higher top speed then increase the values in the bottom end of the table. the highest value I have on any engine is 200 and that's probably a bit fast.

You cant get an exact match at all speeds but is vastly better than the basic profile and nobody can count the chuffs beyond half speed without slow motion filming. You just set it to something which sounds reasonable.

[96RAF]

Let me try to expand on the logic behind fiddling with these complex speed table values.

TXS chuffs are recorded as a series of steady speed clips, as many as 18 such chuff bands across the full speed range. A constant dynamic recording (stop to max to stop) is extremely difficult to synchronise across the speed range. Add to that trying to cater for light engine to heavily loaded.

There comes a point in the speed step table during accelerating where a chuff recording changes from one recorded band to the next, etc, ditto upon deceleration.

In the diesel and electric loco world these are called transition windows and they can be adjusted by a range of CVs as explained in the famous manual.

What you are trying to do here with the steamers is similar by looking for the best match chuff recording band for a range of speed steps, whereupon there is a transition to the next chuff band recording. As stated there comes a point where the eye cannot actually see the chuffs per wheel rotation, but they still have to ‘sound’ right versus the loco speed. This is where the higher value adjustments are useful.

It is expected that the steam generator models will have an interrupter disk to accurately trigger the lower speed chuff rate, but will revert to fixed transitions at higher speeds beyond visual detection.

[Pendragon Sailing]

Many thanks for all the suggestions chaps, and to Rob and LuLuJo in particular for their explanations and CV setting recommendations. I’m off to play with my A2 and Jubilee settings………I’ll report back.

But, what about Diesels? Are the CV curve settings similar or should they follow a different pattern?

[96RAF]

The diesels of course do not need wheel synch as they operate on speed notches (only 3 or 4 depending upon profile a bit like gear changes in a car). As I said these have transition windows that allow the change up and down points to be adjusted. Read the famous manual for more info. Think of this like your automatic car where the gearbox change points can be adjusted by use of snow / normal / sport mode.

[Pendragon Sailing]

Thanks Rob….will do

[WilliamDavid]

I have just set the CVs as per 96RAF’s suggestions, and now find that my four locos seem, somehow, ‘right’.

I don’t know why, what or how, but I am really pleased.

why couldn’t the decoder programmers set these values from the start?

This thread should be pinned.

[96RAF]

I have just set the CVs as per 96RAF’s suggestions, and now find that my four locos seem, somehow, ‘right’.

I don’t know why, what or how, but I am really pleased.

why couldn’t the decoder programmers set these values from the start?

This thread should be pinned.

 

 

Ask Plomax as he started this complex speed curve thing to fettle the TXS chuff rate.

I suppose the same method could be used with TTS and that would be a bonus.

Edit to strike out incorrect info.

[LuLuJo]

I did have a quick look at changing a TTS decoder in the same way in April once Phlomax suggested this. But I could not make it work. From memory I could not find the speed curve values. Not sure they are in the same place as TXS . If it could be done it would be great as I have quite a few.

[Fishmanoz]

Not surprising it didn’t work, TTS decoders do not support this. The motor decoder in these is a very basic R8249 variant.

Check their leaflets to see what CVs are supported.

[LuLuJo]

I did check the leaflets and there was no information about speed curves.

But having said even if the motor control is basic the chuff rate sounds to work in the same way as the TXS decoders. Something must control the changes in chuff rate unless its a straight line progression with equal steps. But then I think the sound would be different.

When I get time I will record a comparison of identical locomotives with the TTS and TXS decoders.

Mike

[Fishmanoz]

No info Mike because there aren’t any. And a significant criticism of TTS on here has been chuff rate.

Great idea to record the comparison.

[96RAF]

The problem with the TTS decoder is that it was a WORM (write once, read many) format. This means that once the sound profile was burnt in at manufacture, then it can not be changed, except for volume of individual sounds.

The fixed relationship twixt speed steps and chuff brackets means the only variable is motor BEMF to establish if the loco is chuffing or coasting.

TXS does not use BEMF in the same way and the chuff to speed step is adjustable to great effect as we have seen.

[WilliamDavid]

I have just fitted a new decoder to my Schools Class with the S15 profile.

As the Schools has 3 cylinders, and the S15 has 2 cylinders, which speed curve is more suitable, 3, 2/4 or neither?

Any better profile for the Schools?

Just to add, with all the fashionable Hornby knocking going on, this install went perfectly.

I love Hornby.

[96RAF]

You are trying to make a 2 cylinder behave like a 3 cylinder so use the 3 cylinder values but if it’s not good then that will be why. You would be better loading a 3 cylinder profile to start with.