Very small decoder (for a Tomix Thomas Train)

[gavino200]

EDIT: This is an old thread recently updated. There are two different decoder installations described. The first is unsuccessful. The second is a success. Skip to the end of the thread for a workable installation description.

 

 

I converted a Tomix 'Thomas the Tank Engine' a few years ago for my son. I think I used a small Digitrax decoder but I'm not sure. There are a few different versions of the Tomix train. I used two different internet write-ups as a guide. Both had the same Thomas with different motors. Both conversions looked good. My Thomas had a third kind of motor that I wasn't able to find online. (They're all the same basic electric motor, but slightly different sizes and shapes). I had to remove the tiny little coal piece at the back, and file the inside of the roof to get my decoder to fit. The decoder is visible.

 

It's always worked well. It pulls Annie and Claribel steadily up a hill. And my son loves it. But I wince a bit every time I see it. 

 

I'd like to redo it. Can anyone recommend a really small basic 4 function decoder that I could use?

Edited December 16, 2018 by gavino200

[VJM]

Why do you need 4 functions?  Unless you have added lights or other things, I don't think 4 function is a requirement.

 

In any case, I recommend the CT Elektronik DCX76z.  One of the smallest decoders on the market (and has 4 functions). 

[gavino200]

Why do you need 4 functions?  Unless you have added lights or other things, I don't think 4 function is a requirement.

 

In any case, I recommend the CT Elektronik DCX76z.  One of the smallest decoders on the market (and has 4 functions). 

 

You're right. I don't. I need the most basic possible. All I need is to control the motor. Forward and reverse. I was using the wrong term. Sorry.

 

What's the smallest, most basic, decoder you know of?

[gavino200]

Mods: Feel free to delete this thread. I think I can fine everything I need in the "DCC Decoders for Motor Cars" thread.

[kvp]

So you probably wanted to write 4 wires instead. I would suggest a cheap and small digitrax 6 wire decoder (DZ1xx range) and just ignore (cut off) the 2 light wires. The Kato motor decoder (EM13) is also a small digitrax decoder with no headlight outputs and some people also use it for Tomytec motors.

[gavino200]

So you probably wanted to write 4 wires instead. I would suggest a cheap and small digitrax 6 wire decoder (DZ1xx range) and just ignore (cut off) the 2 light wires. The Kato motor decoder (EM13) is also a small digitrax decoder with no headlight outputs and some people also use it for Tomytec motors.

 

Yes, That's what I meant. I'm going to school myself a bit about decoders next. Sorry about the confusion.

 

The size of the DZ1 apparently is 8.7mm x 10.6mm which is pretty good.

 

The size of the Lokdecoder DCX76z is 6.9mm x 6.1 mm which is incredible. Nice to know about even if I don't need it this time.

 

I haven't opened the engine yet. Will do in a while when I finish a work task that I'm doing. I'm hoping I can get the one that's in it to fit better with wire reduction and maybe board filing. 

 

Just wanted to have a backup in case that doesn't work.

 

I'll also need to fabricate a new tiny layer of coal to cover the rear coal bucket part. 

[gavino200]

I opened the Thomas engine. It turns out I didn't need a smaller decoder. The solution to fitting it in was glaringly obvious. I can't really understand why I didn't see it the first time. I should never have needed to mess with the engine shell at all.

 

 

This is my original horrible wiring job.

 

 

 

This is the obvious place to put the decoder.

 

 

There are even grooves in the motor housing to pass wires. I can only guess that Tomix designed the unit to be converted this way.

 

 

 

Perfect little piggyback

 

 

I can't know for sure if the 'coal' would have gotten in the way. I don't still have it. But this way is a perfect fit.

 

I don't remember what the decoder is. Dimensions are 9.5mm x 13.5mm. I think it might be a TCS M series. 

[gavino200]

This project was a dismal failure. The ESU decoder was too big. I did some terrible adjustment to the plastic shell to make it fit. And to top it all it had an intermittent stall - likely a positional short of the decoder against the frame. The loco has been in parts in a box for a couple of years now. After persistent request by the little guy to fix it, I decided to take another look at it before committing to buying a replacement. 

 

Fortunately, the motor still ran. This loco is extremely DCC unfriendly. Not only because of it's tiny size. The motor contacts rest on plastic mounts which melt if you try to solder them. As I learnt that the hard way, last time I decided to not remove them now. Instead I tried to solder the contacts as quickly as possible.

 

Also, I now have the tiny D&H PD05A in my figurative toolbox. Actually, Chadbag was kind enough to provide one. There was a time issue as I want to get it going for Christmas as a surprise. It fits very well with room to spare. I've taken to using a little adhesive putty to hold these things in place as it works well and is super easy to remove. 

 

The main task is to repair the damage that I did to the frame. I used some styrene, which seems to work well. The replacement parts are currently drying after priming. Hopefully I'll complete the painting and do the final assembly tomorrow.

 

On test run in DCC it runs well and is able to pull Annie and Claribel up the incline with no difficulty.

 

 

These wires on the loco were for test only. I removed them and used the wires that came with the decoder.

 

 

 

 

Decoder in

 

 

 

 

Back wall of the cabin

 

 

 

Cabin side wall windowframe top

 

Edited December 15, 2018 by gavino200

[chadbag]

As an update, the actual decoder he used is the PD05A from D&H

 

[gavino200]

5 minutes ago, chadbag said:

As an update, the actual decoder he used is the PD05A from D&H

 

 

Thanks Chad. I made the correction. You see why I give these things nicknames? My brain just refuses to process non-descriptive terms.

[gavino200]

I had an idea to create a rudimentary "coal" effect, by poking and prodding a thin piece of styrene. Some of the black primer came off when I cut it to size, so it needs another coat. It's not great but I think it's better than a smooth black piece of styrene.

 

 

 

 

[gavino200]

I finished up the Thomas restoration today. I hand painted the yellow pin stripe on the side of the cabin. I messed up a bit on the circle pin stripe around the back cabin windows. They're too wide. Also, the yellow is too bright. Oddly, after one thin coat with the underlying base coat blue shining through it would have been right. The original train has this shine through effect making the yellow a bit dark. I couldn't help myself giving it a second coat, and worsened it a bit. If it were a "more important" loco I'd redo it. But the little man voted that it was good enough for Thomas so I left it as is. 

 

 

 

Cabin side wall top, hand painted yellow. A little shabby, but passable.

 

 

The final restoration

 

 

 

Thomas takes to the rails again. You can't tell in the photo but he's whistling loudly as he passes the playground. The kids are happy!

 

 

To whom it may concern. I searched this question last week and no answer was available on the internet. Vallejo Model Air "Light Sea Blue" is a perfect match for Thomas's color. Tamiya yellow will work for the yellow pin striping if applied in one thin coat leaving the underlying blue to shine through a bit.

 

Edited December 16, 2018 by gavino200

[gavino200]

In summary. This version of the Tomix n scale Thomas The Tank Engine can be converted to DCC relatively simply using a Doehler & Haass PD05A decoder. 

 

No cutting or alteration of the plastic shell is necessary.

 

Of all the things that I did wrong in my first attempt, the dumbest was soldering to the motor contacts while they were still mounted. It is only by sheer luck the motor survived this. It's impossible to do this without melting the plastic that the contacts attach to. 

 

Instead, carefully remove these and solder wires to them while off the frame. Then replace them.