Very Juddery Scotsman

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Bayf
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Very Juddery Scotsman

Postby Bayf » Tue Jul 12, 2011 11:24 pm

Hey everyone, my first post but I have enjoyed reading things on the boards for some time now. I am fairly new to model railways and it is all a steep learning curve for me.

I have bought most of my stuff off eBay and have been relatively successful. I have an 8 by 4 layout which is kind of like the track mat but stretched out a bit with Somme extra sidings.

The problem i am having is this. I have recently gone to DCC and I have one type 25 diesel loco that works a treat. I am blown away by the acceleration feature. It is smooth all around the track as I would expect. I also have a flying Scotsman that was part of a set. When the layout was analogue it ran really smooth, now it is dcc is it juddery, but only on the straights. I have cleaned the track and am testing the loco on a straight whe the power is. I have also cleaned the wheels so everything is good on that front.

The Scotsman is tender driven and the decoder went in fine and I think is set up ok. It certainly programmed with no issue.

My questions are these (got there in the end!) would you expect the tender to be able to move on it's own without the loco? If so mine isn't which is obviously a problem

Secondly, is my theory that the contact betweethe fender and loco is too blame. When it is going round corners, the contact is made much stronger and so the engine has a good signal.

Does anyone have A wiring diagram of what is going on in the main body of the loco.

I hope all this makes sense and thanks for reading my first post.

Bayf

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Peterm
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Re: Very Juddery Scotsman

Postby Peterm » Wed Jul 13, 2011 2:11 am

First of all, welcome to the forum.

Yes your problem could be caused by the Loco to Tender connection. You need to check if the two fingers / tabs that point upwards are not bent, causing them to touch the stud as well as the rubbing plate. Also, the two contacts underneath which do touch the stud, and that all is clean. These Loco's had phosphor bronze pick ups on one side and via the axles to the chassis on the other, I found this to be unreliable, so I made up a plate and put proper pick ups on the other side too. There's also the screw and spring that fix the connection to the chassis, check that too.

I also found later on, that even though the wheels looked clean, mine was doing exactly what you describe, so in desperation, I used a rotary brass wire brush in my Dremel and gently went round all the drivers with it... hey presto, a sweet runner again.

One more thing, did you take the cap out when you chipped it ?

Edit to say, no the tender won't run on it's own.
Pete.

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thebritfarmer
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Re: Very Juddery Scotsman

Postby thebritfarmer » Wed Jul 13, 2011 2:50 am

Slightly off topic perhaps but is there a reason why they are tender driven?
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Bufferstop
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Re: Very Juddery Scotsman

Postby Bufferstop » Wed Jul 13, 2011 10:08 am

Only an unwillingness on the part of the manufacturers to spend money on doing it properly!
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Bufferstop
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Re: Very Juddery Scotsman

Postby Bufferstop » Wed Jul 13, 2011 10:13 am

Only an unwillingness on the part of the manufacturers to spend money on doing it properly!
I wouldn't leave the connections for a DCC chip reliant on the pin and springy brass of the drawbar. Some pickups on the loco and a wire connection to the tender would be safer.
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Flashbang
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Re: Very Juddery Scotsman

Postby Flashbang » Wed Jul 13, 2011 10:35 am

Hi
If your Scotsman has two contact fingers which sit either side of the central pin but not actually touching the pin, then this service sheet on the Hornby web site should show all you need....
http://www.hornby.com/downloads/service-sheets/?page=3
At the very bottom of the page is HSS 259C Class A1. Click on that link to load the .PDF file

Also carry out the checks below.
Ensure all wheel treads are spotlessly clean
Ensure all rail tops are also clean too.
Now check and clean the inside faces of the wheel wiping contact strips on the loco and the inside faces of the wheels they touch onto. I use a fibre pencil for this.
Look carefully at each wiper contact and ensure it continually remains touching the rear of the wheel even when the wheel is move across the loco. If there is a brake in connection, then gently tweak the wiper so as it is pressing lightly all of the time onto the rear of the appropriate wheel. Use a pair of tweezers or fine long nosed pliers to do this.

Where DCC conversions of tender drive loco are concerned, I always remove the original wires between loco and tender connectors and then hard wire the two together. Fine flexible wires, as used on the actual decoder are ideal for this work and are not really seen when the loco is on the track - I use 2 x black wires but thats my choice.
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Broken? It was working correctly when I left it.

Bayf
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Re: Very Juddery Scotsman

Postby Bayf » Wed Jul 13, 2011 11:36 pm

Thanks for all your help everyone. When I get out in the garage tomorrow night i will have a try of all of these suggestions

Bayf

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K9-70
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Re: Very Juddery Scotsman

Postby K9-70 » Thu Jul 14, 2011 8:40 am

Good advise already given above.
After trying those suggestions and your FS is still running no better,
try adjusting the Back EMF values.
Set the following CV's 54 & 55 to
CV 54 - 05 & CV 55 - 55.

Work up or down in steps of 5 until you get your FS to run smoothly.

K9-70
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Bayf
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Re: Very Juddery Scotsman

Postby Bayf » Thu Jul 14, 2011 11:15 pm

Cheers k9, I like a scientific response, but I confess to not having a clue what you are talking about. I don't know what FS is. I assume EMF to be electromotive force, and I thought CV was either a Coventry postcode or the back 2 thirds of a dodgy French motor.

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Flashbang
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Re: Very Juddery Scotsman

Postby Flashbang » Fri Jul 15, 2011 10:18 am

Hi Bayf

What DCC control system are you using?

Taken from the Brian-lambert web sites DCC page..... http://www.brian-lambert.co.uk/DCC.htm

Configuration Variables (CV) control the way the decoder controls various functions within the loco or accessory. They are 'memory slots' where a specific piece of information is stored for a specific operation. CVs settings are retained even when the console is turned off or in the case of a loco decoder, when a loco is removed from the rails etc. Most CVs can be altered, except for a couple which hold manufactures data about the actual decoder and its software version (CVs 7 and 8). But most are adjustable and by fine tuning a particular CV from its default setting, better or finer control over that operation can be achieved. The most basic CV that virtually everyone using DCC will adjust is CV1. This sets the mobile decoders address number (default setting is always 03). Other CVs such as acceleration and deceleration rates (via CVs 3 & 4), the maximum fastest speed permitted (Top Speed via CV5) and lighting control CVs i.e. those that control the way the locos lights operate etc are then next group often to be fine tuned by the user. Think of CVs as a bit like being a radio with pre set tuned radio stations buttons. So the position 1 button on the radio when pressed gives you a specific radio station, but by fine tuning button 1 you can then make the radio receive that radio station better or worse. Similarly, CVs are turned, but they only alter the function or operation they are designed for. So for example; you can alter CV3 value and make the loco accelerate away more slowly from stop, by increasing the number (called the 'value') entered into CV3 when its being set. But you can't make CV3 become the Top speed CV which is CV5.
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Broken? It was working correctly when I left it.

Bayf
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Re: Very Juddery Scotsman

Postby Bayf » Tue Jul 19, 2011 1:38 pm

Thanks Flash, that makes a lot more sense and is a really useful post. Lots of bedtime reading in the whole site.

I am using the Hornby Select, so I dont know if I will be able to edit any of the settings. I have to say, it woudl be useful to edit the top permitted speed.

Bayf

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Flashbang
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Re: Very Juddery Scotsman

Postby Flashbang » Tue Jul 19, 2011 2:21 pm

Bayf wrote:<Snip>
I am using the Hornby Select, so I dont know if I will be able to edit any of the settings.
<Snip>
Bayf

Hi
Unfortunately the Hornby Select cannot alter CVs other than those its pre set to do - Address number, acceleration & deceleration plus normal direction of travel.

You would need a more up market DCC system or obtain a SPROGII to be able to write CVs needed to adjust motor control.
Most better DCC systems and the SPROGII too can also read the values set in CVs too.
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Broken? It was working correctly when I left it.

Dead_dog
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Re: Very Juddery Scotsman

Postby Dead_dog » Thu Aug 11, 2011 1:30 pm

Ok, I have a friend with Hornby Select and Bachmann Branchline 36-552 Decoders, and he has complained that the system does not run properly, only 'judders'....
I read somewhere on the internet about a design incompatibility and EMC, so I was able to sort the problem by fitting a ferrite choke in one of the feed wires between Select and track. I ended up using a large ferrite torroid, about 30x15x7mm ring, from a computer/switch mode supply, and threaded the feed wire 5 times through the ring to make up 5 turns for about 20 Micro H. This had the effect of squashing spikes and slowing the Select's drive edges enough for the DCC decoders to operate correctly...
'Juddering' returned with fewer turns, but there was no observable change with a few more, so and error was the way. Of course too many turns may have caused other prolems...
I am sure someone can perfect this process as a 'quick fix' to an existing layout, but for the moment my friend is happy....
I hope this could be of help to others....


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