Can Ichange the direction my loco runs on DCC?

[TEAMYAKIMA]

OK, I guess that topic title is a bit odd - let me explain.

 

I have a tender loco which I want to run as tender-first when in forward. How can I change that please?

[DK123GWR]

12 minutes ago, TEAMYAKIMA said:

OK, I guess that topic title is a bit odd - let me explain.

 

I have a tender loco which I want to run as tender-first when in forward. How can I change that please?

Add 1 to the value of CV29.

[WIMorrison]

3 minutes ago, DK123GWR said:

Add 1 to the value of CV29.

Not quite correct, the correct action is;

 

read cv29 and if it is EVEN add 1 to the value and write it, if it is ODD then subtract 1 from the value and write the value to the decoder.

[Michael Edge]

Swap the motor wires over, CV29 can be a can of worms.

[WIMorrison]

2 minutes ago, Michael Edge said:

Swap the motor wires over, CV29 can be a can of worms.

1st April was last week.

[Michael Edge]

I wasn't joking, I've seen alterations to CV29 cause all sorts of problems depending on which decoders and DCC systems are used, I prefer to keep it simple.

[WIMorrison]

CV29 is a mandatory CV and is fully documented operating in the same way on all decoders.

 

there is nothing in CV29 that cannot be undone and similarly there is no setting of CV29 that will cause issues with any decoder. The worst that could happen is that you set an incorrect bit which is easily rectified by writing the correct value.
 

At no time will you lose the ability to program the decoder and you should never resort to changing the wiring to simply change the direction of a loco.

 

I hope that the OP and others ignore the ‘advice’ that you have provided as it is preposterous, though fortunately it is impossible to undertake in many modern locos.

[Colin_McLeod]

It worked for my pair of Hornby Dublo 3 rail* 'nose to nose' class 20s lol 😅

 

 

Not DCC though!

[SamThomas]

1 hour ago, Michael Edge said:

Swap the motor wires over, CV29 can be a can of worms.

Not much of a solution if the locomotive has directional lights...............

 

If you are concerned with what effect changing any CV is all you have to do is note what it is prior to changing it then, if anything else is effected you can easily revert to the original CV setting.

[TEAMYAKIMA]

1 hour ago, Michael Edge said:

Swap the motor wires over, CV29 can be a can of worms.

 

Thanks for the idea Michael, but I think the CV29 idea is more suitable as I may need to swap back and forth several times and certainly when the loco is finally sold

[Crosland]

1 hour ago, Michael Edge said:

I wasn't joking, I've seen alterations to CV29 cause all sorts of problems depending on which decoders and DCC systems are used, I prefer to keep it simple.

 

That's why the advice to "add 1" was corrected. If you use CV29 as it is intended there will be no problems.

[Michael Edge]

49 minutes ago, TEAMYAKIMA said:

 

Thanks for the idea Michael, but I think the CV29 idea is more suitable as I may need to swap back and forth several times and certainly when the loco is finally sold

In that case I agree with you but my comments were based on practical experience.

[WIMorrison]

3 minutes ago, Michael Edge said:

... practical experience

 

A better term to use might be inexperience 😉

Edited April 8, 2022 by WIMorrison
emoji issues

[Michael Edge]

Really! How young are you and how long have you been in this business?

[WIMorrison]

Clearly longer than you from this post - hopefully your advice elsewhere is more accurate than your ill-informed suggestion here.

[DK123GWR]

2 hours ago, WIMorrison said:

Not quite correct, the correct action is;

 

read cv29 and if it is EVEN add 1 to the value and write it, if it is ODD then subtract 1 from the value and write the value to the decoder.

True, but every decoder I've used has taken an even value by default, and I was operating on the assumption that this one would be too. I suppose that if the loco is pre-owned a previous owner might have wired the decoder in reverse and already changed CV29 to correct the error.

[dhjgreen]

3 hours ago, TEAMYAKIMA said:

OK, I guess that topic title is a bit odd - let me explain.

 

I have a tender loco which I want to run as tender-first when in forward. How can I change that please?

Using a Sprog and Decoderpro the label is normal or reverse and deals with the detail.

[njee20]

4 minutes ago, DK123GWR said:

True, but every decoder I've used has taken an even value by default, and I was operating on the assumption that this one would be too. I suppose that if the loco is pre-owned a previous owner might have wired the decoder in reverse and already changed CV29 to correct the error.

Pretty big assumption, Iain’s advice is better, although yes, adding one will often have the desired effect.  
 

18 minutes ago, Michael Edge said:

Really! How young are you and how long have you been in this business?

 

No need to get so defensive, I have to agree with Iain that swapping motor wires over is a sledgehammer to crack a walnut, as well as having the potential to cause downstream problems. Any issues you’ve had with CV29 previously are the result of user error rather than anything untoward. 
 

The 2mm Scale Association has a handy calculator for working out CV29 settings here: http://www.2mm.org.uk/articles/cv29 calculator.htm

[RAF96]

Prior to fiddling with any wiring you should have ensured the loco is  wired for correct DC running according to convention, this being with the loco facing  forward, power is applied with positive to the right rail and the loco moves forward. Once you know the loco is wired properly, then fiddle with your CVs.

[njee20]

He’s already said that it does; but he wants ‘forward’ to be the opposite to convention. No fiddling with wires is necessary. 

[Michael Edge]

1 hour ago, WIMorrison said:

Clearly longer than you from this post - hopefully your advice elsewhere is more accurate than your ill-informed suggestion here.

You're the one who started being rude, I made a practical suggestion and asked a polite question which you have chosen not to answer. 

[SamThomas]

I've changed CV29 in the past to "reverse" the "normal" direction of a locomotive with nos issues.

 

Probably 50% of my diesel & OHE fleet are reversed so that the "normal  forwards" is from the #2 cab end as per real life.

[boxbrownie]

CV29 is a bit of a pain with the new ESU V5 decoders, since they have not allowed three step speed mapping in the new EU/U.K. decoder series, don’t try that with them it had me stumped for a while!

 

[WIMorrison]

The default setting of CV29 in the ESU V5 LokSound and LokPilot decoders is 12 which means that DC running and Railcom are enabled. Unfortunately bit 1 is set to zero which means that you need to enable bit 1 by making CV29=14 to get 28/126 speed steps. This is the only CV29 issue with ESU v5 decoders. 

 

If you wish to disable CVs, 2, 5 and 6 and use a custom curve then you would need to add 16 to the value in CV29 (assuming it isn't already enabled).

 

You will find this webpage (written by @Nigelcliffe I believe) extremely helpful in setting CV29 correctly.

 

DCC CV29 Calculator (2mm.org.uk)

[Crosland]

2 hours ago, DK123GWR said:

True, but every decoder I've used has taken an even value by default, and I was operating on the assumption that this one would be too. I suppose that if the loco is pre-owned a previous owner might have wired the decoder in reverse and already changed CV29 to correct the error.

 

Yes you will often get away with it, in a similar way that many people get away without following best wiring practices for DCC.

 

The real problem is that people see the advice to "add" or "subtract" and read across to other bits in CV29 which might already be set. Adding or subtracting will then cause a carry or borrow into the more significant bits, messing up other settings. That's when the fun really starts and is, I suspect, the source of other peoples issues with setting CV29.