The Snapper's DCC Workshop - July 2023 Update - use threadmarks to find - Little & Large

[TheSnapper]

When a friend asked me to install a sound decoder into his 0 Gauge Heljan Railbus, I thought, OK, this is a quick simple job – a plug-in 21-pin decoder, space already for ESU 23mm speaker, room in the roof for a stay-alive unit (which is really is really essential for this 4-wheeled vehicle).

I was wrong, of course; it turned out to be a bit more involved and time-consuming.

Beneath the driver’s cab at one end, there is a removable cover which reveals the chamber ready to accept an ESU 23mm speaker.



The instructions for fitting the speaker indicate that at the same end there is a small hole in the inner roof, leading to a conduit in the driver’s cab down which wires can be fed into the speaker chamber.

First of all I couldn’t find the conduit; I had to line-up it up with the hole, by tweaking the position of the driver’s compartment. I then found that there was no way through the floor into the speaker chamber. So using the sharp end of a scalpel & a pointed grinding tool in the Dremel I carefully created a small opening. I then used a length of brass rod to poke a way through.





The speaker wire needs to be very fine as there ain’t much room for thicker stuff through the conduit. I soldered the 2 ends of a loop of ESU Decoder Wire (part # 51940 - 51949) to the end of the brass rod & pulled it through, like a thread on a needle.



Hopefully the photos will explain better than words.

After removing the blanking plug, the decoder fits easily. I used a Zimo MX644D from Digitrains, loaded with their AC Railbus sound project, created by Paul Chetter.



Next problem is where to attach the speaker wires at the decoder end. Usually there are 2 solder pads or holes on the native PCB, but nothing was obvious.

Research required – Google-is-your-friend time!

I discovered that Paul Chetter had written an article on installing sound decoders for both the 00 gauge & 0 Gauge versions of the Heljan Railbus, in Hornby Magazine for October 2015. Not having the magazine, I dug further into the Internet & managed to download a PDF copy from PDF Magazine Download - Catalog popular PDF journals . I chose the free download, which was quite slow; I believe you can subscribe for a quicker service if required.

This showed me all I wanted to know. There is a micro-socket on the board labelled CN6 which is for the speaker wires. Problem is there is no plug supplied! And if there would have been, it would be nigh impossible to connect wires to it, as it would be too tiny. A plug with a couple of flying leads to connect to would have been ideal (I did once try to source some of Heljan’s plugs & sockets, but they would only sell me 10,000!).



The answer revealed in Paul’s article was to solder directly to the base of the relative pins on the decoder connection. This was very tricky and needed a steady hand and a fine bit on the soldering iron. After a couple of attempts, I managed to do it, making sure there were no bare wires shorting, which would have been disastrous to the decoder.



The holes & openings in the speaker enclosure were sealed and the unit wired-up and installed on the underside of the chassis.



Fitting the stay-alive unit (a compact Zimo SC68 unit) was straightforward – it solders directly to 2 pads on the decoder. Just need to make sure the wires are fitted the correct way around! I insulated the casing with shrink-wrap, and fixed it to the roof with double-sided tape.

And so to testing. Although the overall sound was really good, I found that with the default decoder settings I couldn’t get the characteristic gear-changes to occur until the Railbus was going too fast. There are 4 changes in all.

The ever-helpful Mr Chetter replied to an enquiry I posted on “the other place”, to say that it is possible induce a gear change when the engine idle sound or the cruising sound is playing, by reducing the throttle and immediately increasing it again, just like you would when driving a car.. The gear change will occur, followed by acceleration sounds.

However, I wanted the gear-changes to sound automatically within a reasonable speed range, without having to fiddle with the throttle. I tried lowering the maximum speed (CV5), changing the momentum (CV3 & CV4) and using Decoder Pro to change the speed curve, without too much success.

The breakthrough came when Paul suggested I adjusted CV57, which according to the Zimo manual, reduces top speed by reducing the voltage to the motor and effectively 'compresses' the gear changes into a lower speed range.

CV57 changes certainly made the difference - I can now get the full 4 gear changes automatically in about 15ft of test track, without adjusting the throttle.

These are the settings I ended up with

CV 57 set low to =30
CV3 = 50
CV4 = 60
CV5 =1 (=255, default)
CV6 - 120 (default)

I also used Decoder Pro to set the speed curve to a log curve.



See here for information on setting speed curves using Decoder Pro:
Comprehensive Programmer - Speed Control Pane

Of course these settings may change slightly as time goes by, but it’s a start!

….and then we had another problem, or rather 2 problems.

On the layout, the Railbus kept derailing when negotiating point-work. Initially we thought it was due to the long rigid wheelbase, through admittedly tight check-rails, but when checked against a BR Mk1 Horsebox, it was virtually the same. Also the lights both back & front kept flickering on & off, no matter which direction the model was running.

Eventually we checked the back-to-back measurement and it was quite a way out on both wheels. In fact one was worse than the other. So we removed the keeper plates, extracted the wheelsets and managed to carefully persuade them outwards to the required 29mm.

On replacing the wheels, we ensured that the pickups were making really good contact, as we suspected this was the cause of the flickering lights.

Testing again on the layout point-work, all was well and gone were the flickering lights. My friend is pleased.

Anyone else had problems with Heljan back-to-back measurement?

 

[TheSnapper]

Request for Help!

Has anyone any ideas what this may have sounded like:



This is a customer commission which was largely scratch-built by David Amias, apart from the cab and firebox.

Cheers

Tim

 

[TheSnapper]

The GW Theme continues......



Although I prefer to install everything on the loco chassis, sometimes it is not possible.

On this model, there was no room in the frames due to the dummy inside motion etc.




Fortunately, the boiler was hollow enough to accommodate the decoder (Zimo MX645) & stay-alive capacitor (Digitrains “Zimo- SC68 equivalent”).




The capacitor was clear-shrink-wrapped and then wrapped together with the decoder with an oversize piece of black sheathing to form a double insulated package. The idea is to avoid any chance of shorting, as it would be loosely located in the boiler.



For the same reason, I wrapped some Kapton tape around the top of the motor





The only place for the Zimo cube speaker was behind the motor. I had to move the pinion gear temporarily to one side to fit it in. I used Araldite to fix it and it works well.





Final testing could be done with the decoder package resting on the dummy inside motion!

 

[TheSnapper]

Decorated a Heljan Triple Grey 37/4, as 37 413.
This will get a large Zimo decoder with Paul Chetter’s latest 37 sound and a big Tang-Band speaker.

Large Zimo decoders seem currently to be in short supply, so I decided to re-use one from another project.


I purchased the relevant soundfile from Digitrains and uploaded it to the decoder using my Zimo MXULF device.





Heljan’s later models have multi-coloured wiring but the 37 came with the original red & black scheme, so before removing their PCB, the wires need to be labelled.
All the red wires are common positive, and all lights tested OK.





To mount the decoder, I use Plastruct section (whatever is handy) glued to the chassis.
Rather than connect leads for motor, pickups & lights directly to the decoder, I now like to “anchor” them securely.


This also enables connection to the decoder with a single wire for motor, pickups & common positive .
For this, I use a piece of copper-clad sleeper, divided into 7 sections in this case. It does help to identify the sections with a label.



The decoder is fixed to its mounts with 4 small screws, and all connections made.





The large Tang-Band T1-1931S speaker needs to be well anchored down due to the low-frequency vibrations produced. It is screwed to a strip of wood (nicely inert MDF) which is fixed to the chassis with Devcon epoxy adhesive.
Obviously, the underside of the loco tanks is removed to let out all the lovely GROWL!

 

[TheSnapper]

The Snapper’s DCC Workbench – June2023 – Little & Large

It’s been quite a while since I posted anything new in this thread – looks like over 3 years to be exact.

Not that I haven’t been busy, with mostly run-of-the-mill installations, which I didn’t consider being worthy of writing about, to be honest. …. Except perhaps I ought to have mentioned that twin motored diesel that would only run satisfactorily when back-EMF was disabled, or the exquisite, professionally built (i.e., expensive) GWR “Armstrong” which required handling with kid-gloves, or the Dapol 121 which ran like a pig…etc.

However, I thought you might be interested in this pair, which were so challenging, in their different ways, and in how the difficulties were overcome.



The 9F is well-built from a DJH kit and the tiny loco on the right is a scratch built S&D “Dazzler.

The Large - DJH 9F

Removing the body of this big heavy beast revealed a massive Bühler motor, which combined with the weight of the thing (2.5Kg) immediately made me think that I would need to install a larger, more powerful decoder than the “normal size” we use for the majority of 7mm locos.



Problem was that there was absolutely no room in the loco itself as the boiler was virtually sealed, except for a very small hole (more of this later)



So, the only alternative was to mount the decoder in the tender, which incidentally was also sealed!



Therefore, to accommodate the chosen Zimo MX699Ks narrow decoder & mounting board a large hole had to be cut in the tender “floor, with a lot of trial & error to ensure a good fit:



Note the insulation tape to protect the side frames.

The loco picks-up on the tender wheels as well as all driving wheels, and already had a plug connection fitted between loco and tender, so wiring-in the track feed to the decoder was reasonably straightforward:



However, an additional 4-pin plug was required to be able to connect the decoder to the motor & speaker, which is hidden when loco & tender are coupled:



Ah yes, the speaker! What to use & where to put it?
Certainly, the 9F need a largish speaker to sound convincing.

The only solution I could think of was to somehow make use of the boiler barrel as an enclosure with a speaker firing through the small hole as shown above.


The biggest speaker I could find to almost fit was slightly too deep at 15mm, so I bit the bullet & cut off the back (and the fixing “wings”):

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This was then fixed with epoxy & sealed into the loco body with the rear of the speaker firing into the small hole.

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Finally, to avoid a slightly “hollow” sound, I blocked off the chimney to the outside world, making the boiler, in effect, a sealed enclosure.

The loco runs & sounds great and was worth the extra work involved.

Note that, unusually, I have not yet fitted a “Stay-Alive” unit, due to the all-wheel pickup and sheer momentum of the model when running. We’ll wait & see if it needs one….

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The Little – S&D Dazzler​

Despite having some knowledge and interest in the S&D, I had never come across this loco before; and it was one of a pair into which I had to install sound. Both were scratch built by a friend of mine – in fact I think he built 10 in total for himself and other people!


With a sealed boiler and virtually no room available to hide things from view, obviously “normal” components could not be used, so the initial task was to find a sound decoder small enough to fit onto the front of the motor.

I went for a Zimo MS550 which is incredibly small and promised to be powerful enough to drive the tiny motor.

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Bear in mind, each square on the background grid is 1cm


This was fitted to the motor, and wrapped with Kapton tape for insulation:

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The capacitor tucks up above the motor when the body is attached.

Next task was to find a speaker that could be fixed unobtrusively on the frames and the 26 x 14 x 7 fom Roads & Rails fitted the bill. See here:

26x14x7 Bass Enhanced DCC Sound Speaker (4 ohm)

Very compact bass enhanced speaker for DCC sound use. Measures just 26x14x47mm so is ideal for small OO gauge locos. It provides better bass than a sugarcube speaker. It is fully enclosed and ready to use.

www.roads-and-rails.co.uk

This fitted neatly onto a chassis cross-member and sounds great for its size

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Despite its diminutive size the loco runs well & sounds great.

I think the decoder is amazing for its size and the speakers is a revelation too.

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