EMD DD35 with Body Mount Couplers – Part 3

Back in January of 2019 I shared with you my test print for an EMD DD35 with body mounted couplers in N Scale.  You can find the post here.  This week I thought you’d like to see what it looks like with a bit of colour.

The shell, as pictured below, is stark white having been 3D printed in Shapeways’ Fine Detail Plastic, also know as FUD (Frosted Ultra Detail).

With the pilots 3D printed as part of the body, the only two parts are the main shell and the fuel tank.  This locomotive will be Southern Pacific 9900.

But, as with most SP locomotives this one won’t stay this clean for long as it’s going to be weathered.

Weathering can be done in many different ways, and to many different levels.  This locomotive will be weathered with enamel paints using an airbrush, and typical for the SP it will bit fairly grubby.

The locomotive will now need a good wheel clean to remove any paint, as it always gets on them, and then it’ll be ready to run.

The DD35 kit with body mounted couplers is available here.

Sad News From The Deeping Model Railway Club

This week I have some sad news from the Deeping Model Railway Club.

For the last twelve years they have held the Stamford Show and this year it was to be on the 18th of May 2019 at the Stamford Welland Academy.  As with most of the shows I attend, and the one I organize for the Poole & District Model Railway Society, most of the traders and larger layouts set up the day before.  Unfortunately in the early hours of the morning the premises was broken into and the layouts and trade stands were destroyed.

The secretary for the Market Deeping Model Railway Club has set up a crowd funding page in which he says:

“Market Deeping Model Railway Club needs your help to rebuild. We have held our annual show in Stamford for the last 12 years. Months of planning goes into the show and years of work goes into building the layout. Imagine our horror and grief when we were greeted by this scene of absolute devastation on the morning of 18th May 2019. Some of the models on display are irreplaceable and whilst money cannot possibly replace the hours of painstaking effort that has been so wantonly destroyed, we would ask that you make a donation, no matter how small, to help us get back on our feet. Please accept our thanks in advance.”

The link to the crowd funding site is below.


Links to news stories in the press:

Deepings Nub news 


The Rutland and Stamford and Mercury 


I hope the The Deeping Model Railway Club can rebuild and recover from this devastating incident.

Choosing The Right Speaker For Your Sound Decoder

This week I have a ‘how to’ post to share with you about speakers and the importance of choosing the right one.

Sometimes I get locomotives in for repair which have been fitted with a DCC sound decoder and the sound simply doesn’t work.  There are several reasons for this and hopefully it’s something simple like a broken wire.  But sometimes the wrong speaker has been used and it’s damaged the decoder beyond repair.

Most manufactures supply speakers with their decoders, but as they often don’t know what you intend to fit it in, the speaker is a generic size, and in N scale this is never going to fit.  There are all sorts of sizes available as well as shapes as you can see below from this selection I had in my bits box.

Two of these speakers are supplied with ESU V4.0 decoders, the smaller speaker comes with the V4.0 Micro.  However, both are fairly large and it can be struggle to find room for them in many locomotives.  So they are often swapped for smaller speakers.  These then become available to be used with other decoders, after all they’re good speakers, but now there’s a potential problem which could damage the decoder, because they may not be compatible.

Speakers are measured in wattage, this is how much power they can handle, and impedance, which is the property of a speaker that restricts the flow of electrical current through it.  This is measured in Ohms.  If you put too many watts through a speaker, you normally just blow the speaker.  But if the impedance of the speaker is too low then more power is used in the amplifier than sent to the speaker and the amplifier over heats and blows.  The amplifiers on DCC sound decoders are ‘solid state’ which means they are made from electrical components only, no form of valves or vacuum tubes as you used to get in guitar and stereo amplifiers, but given how small the sound decoders are that is not surprising.  But this means there really is no tolerance for getting the impedance wrong.

Some speakers, such as the ones used by ESU with their V4.0 decoders have both values written on the back; 1.5w and 4Ohms.

If this speaker was used with a standard Digitrx, Zimo or Hornby TTS sound decoder it would blow the amplifier right away as these decoders are normally only rated at 8 Ohms.  The lower the Ohm value the more power runs through the amplifier.

All sound decoder manufactures should list, either in the decoder manual or on their website, what the max Ohm value is for their product.  But what if you have a speaker and you don’t know what the Ohm value is?  This can easily be measured with a multi meter which can read Ohms.  Below you can see I have the multi meter set to read up to 200 Ohms and when connected to the ESU speaker it is reading 4.3 Ohms.

So now you can select the right speaker to go with your sound decoder.  But going with the smallest isn’t always the best idea.  Normally the smaller the speaker the quieter it gets and it will have less bass.  One of the best ways to increase the volume and bass, without electric amplification, is to add a chamber to the speaker for the sound to reverberate in.  Putting a speaker inside a locomotive shell will do this naturally as the shell forms a box.  But the shell will not be airtight and as a speaker makes noise by pushing air the increase in sound will be small as the air escapes.  Adding a chamber directly to the speaker is the best way and the ESU speaker I measured earlier has just this.  The speaker clips into the box.  But due to the screw holes in the speaker plate and the wire holes it still isn’t airtight.

Digitrax supply their N Scale speakers with a pull-off strip which leaves a sticky surface around the speaker.  It can then be stuck to the chassis or inside of the shell.  But this doesn’t leave a lot of air for the speaker to push against.

I like to use cell phone speakers for my N scale locomotives as cell phones can be very loud!  Below is a Zimo sound decoder with a 8 Ohm speaker.  When soldering the wires onto your speaker remember that a speaker has a large magnet in it so as the soldering iron gets close make sure to hold the speaker down so it doesn’t jump up and attached itself to the iron.  They tend to get very hold and melt very quickly; don’t ask me how I know this!

In cell phones the speaker normally sits over a cavity and is stuck on to form an airtight box.  This is why some phones sound very loud and appear to have good bass.  I 3D print boxes to go with the speakers in different depths depending on how much room I have to work with.

This particular sound decoder is going into an old Rivarossi Challenger and that has lots of room in the tender so I’ll be using the larger box.

I use superglue to fix the speaker but it’s important not to get any on the actual speaker.  So, using the speaker bag, I put some superglue down and rub the box in it ensuring I get some glue on all sides.

Then I place the box onto the speaker and hold it till the glue sets.  Being superglue this doesn’t take long.

The speaker is now ready to fit into the tender and it will be considerably louder than any of the speakers in the first picture.

The thing to remember is to check the impedance.  Most new decoders now support 8 Ohm speakers, ESU going up to 4 Ohm. But a lot of older decoders, even ESU, may be 32 or even 100 Ohm only.

If anybody is interested in 3D printed speaker enclosures or cell phone speakers please get in touch via the contact page.

Bachmann N Scale 4-8-4 Replacement Gears – Part 2

In February of this year I shared with you my set of replacement 3D printed gears for the Bachmann N Scale 4-8-4, 3rd Generation.  You can find the post here.

At the end of the post I needed to make some modifications to the gears as the axels were still a little too loose on the wheels and the twin transfer gear was way too loose.  These changes were made and another set was 3D printed.

This time all the gears fitted well into the chassis, but I think I still have a problem with the twin gear as the motor struggles to drive all the gears.  Either the larger set are oversize, causing resistance between the gear and the worm, or the smaller set don’t have a deep enough trough between the teeth, which means the axel gears push the twin gear up into the worm.

With the original twin gear fitted, and all the other 3D printed gears fitted, the assembly runs smoothly.   Below you can see the axels fitted onto the wheels with the chassis plate installed.

With the entire chassis assembled I started testing the gearing and discovered that there was a bind at the same point in every rotation.  After a little adjustment I was able to get it to run much smother.  However, on reflection the next time I do this when fitting the gears to the first set of wheels, as shown above, I’ll attempt to get the gears positioned at the exact same point on each wheel, as I think it was this that caused the issue.  If, as with diesel locomotives, there are no side rods, the position of the gears is not so critical as they will find their place.  Or if there are no internal gears, simply side rods as with the HO 4-8-4, then it’s just the quartering which needs to be correct.  But as this loco has both internal gears and side rods, the quartering needs to be correct as does the gear positions relative to each other.

Below is a quick video of the chassis running with power supplied direct to the motor.

I’ll make the adjustments to the twin gears and do another test print, but in the meantime if you’re keen to get your N scale 4-8-4 back on the road and are happy to use all the other gears then a set is available here. In most cases, these 3rd generation 4-8-4 locos only need the axel gears to make a full repair as it’s the axels that split.

Once the new set arrives I’ll update you with the progress in a later post.