Consistent Inertia

[St. Simon]

Hi,

 

At a recent exhibition the biggest complaint of my operators was that my DCC fleet had inconsistent inertia and acceleration / braking characteristics. So I have resolved to fix it and I have two questions.

 

1) I have calculated the values for CV 3 and 4 for acceleration and braking I require. How does this affect syncing of a sound decoder and movement? I don’t think it would too much, but I need the opinions of more knowledgeable people!

 

2) How do I go about setting up a non sound decoder to delay starting away when coupled to a sound decoder? Im

sure I’ve already seen a topic for it, but I can’t find it!

 

Simon

[RAF96]

1. The easy way to think of CVs3&4 values is to compare them with the weight of your train, a light train his alow value and a very heavy train is a high number. It shouldn’t affect your sound as this is tied to the throttle setting vs actual achieved speed by the sound provider.

2. If this facility is available it will be in your decoder instructions..

[St. Simon]

Hi,

 

A further question on this is is there any easy way of working out the values of CV3 and CV4 so that every brakes in a certain manner?

 

What I am trying to do is to set up the braking such that everything stops with in a certain distance, in my case in 4ft from a certain speed step.

 

I’m guessing the answer is to pick a speed step and then find the CV4 value through trail and error, but I’m hoping that there is a easier way of calculating the value as setting up a test track to do the trail and error is a pain!

 

Simon

[WIMorrison]

You need to know what decoder type is fitted to the locos in question as this should enable you to work out how long (in time) they will take to stop

 

For these decoder makes, this is the time per speed step;

 

Zimo=0.9 second per step in CV4
D&H=1.0 second per step in CV4
ESU v3 & v4 = 0.25s
ESU v5 LP/LS5 = 0.25s, except LP/LS5DCC = 0.896s
Märklin DCC = 0.9s

 

What this means is that if CV4 is set to 33 in a Zimo decoder, then it will take 33 * 0.9 = 29.7 secs to go from full speed to stopped (speed step 255 to 0). 

 

If you have a smaller range of speed steps e.g. CV2 is 8 and CV5 is 172 then you will take (172-8)/255 * 29.7 = 19.1s to come to a stop.

 

I hope that this makes sense and it helps you. Perhaps some else knows the time per step for other decoder makes and will list them in this thread to assist you in your quest.

[rogerzilla]

If you have a brake feature on your decoder, it may be better to set CV4 to a high value (try 150 for a Zimo decoder) and use the brake instead.  Less guesswork about where the train will stop, and arguably more realistic.

[Ray H]

There are CVs that let you determine the physical length of the braking distance.

 

We've used this on our club's O gauge layout and a colleague has done similar on his layout.

 

It takes trial & error and can be great fun as you wonder why altering a CV's value by just 1 can make a noticeable difference when the previous alteration by a similar amount made no apparent difference.

[WIMorrison]

1 hour ago, Ray H said:

There are CVs that let you determine the physical length of the braking distance.

 

This is dependant upon the decoder brand that is in use.

[Ray H]

23 minutes ago, WIMorrison said:

This is dependant upon the decoder brand that is in use.

 

We've managed it with both Zimo & ESU sound decoders, we've not had cause to try it with any non-sound ones.

[RAF96]

The basic formula for CVs 3 and 4 is told on the NMRA web-site.

Some decoders can be set using other CVs for constant stopping distance - eg Lenz.

I prefer to use dynamic braking (again decoder dependent) as the rate can be set for individual locos such that they will all stop on the mark from their usual line speed.

[Nigelcliffe]

4 hours ago, RAF96 said:

The basic formula for CVs 3 and 4 is told on the NMRA web-site.

 

And ignored by some decoder brands.     Even big names:  ESU for example has its own braking distances on the UK/EU versions of decoders, but NMRA braking formula for the US-market versions.  

 

- Nigel

[WIMorrison]

4 hours ago, Nigelcliffe said:

 

And ignored by some decoder brands.     Even big names:  ESU for example has its own braking distances on the UK/EU versions of decoders, but NMRA braking formula for the US-market versions.  

 

- Nigel

 

Which is why the ESU decoders I mention earlier have two figures for the CV3 and CV4 speed step values - EU and US 😅