BR-18.5 - MINITRIX 12456
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Minitrix BR 18.5

03/17/14, 10/09/15- I needed a loco for some old Arnold Rheingold coaches I'd bought on eBay and the BR 18 was the loco of choice for this duty. It's a short 4-6-2 loco that has as many wheels as I can run on my layout's tight curves. I went through several twists and turns before getting the Epoch III version. The first one (Minitrix 12312) was an Epoch II DRG version with brass boiler bands-- very pretty, but it was lost by the postal system. The second one (Minitrix 12365) was absurdly pricey but equipped with a sound decoder. Fortunately or not, after pressing the "buy" button, I was told that it was actually not in stock. So the 12456 wasn't my first choice, but after fitting it with a LokPilot, I was relieved. When I committed to getting the sound-equipped version, I believed that the factory-installation had special magic that I couldn't hope to achieve. I still believe that the factory can do a much better job of fitting the decoder and speaker in the limited confines of an n-scale loco-- this is stuff you can see. But most online catalogs are sparse on the performance particulars. I want to know which/how many sound functions are built in and how good it sounds. "Pretty good given the technology at the time?" I've become wary of getting an older model loco with an older sound decoder that I can't program, especially when you pay a premium for the honor. The ESU stuff has made me realize how cool it is to be able to choose sounds what sounds you want (prototypical or not), and to program the decoder's operation.

The loco itself is great-- metal tender and engine, with the motor mounted in the engine body. The socket for the decoder is mounted in the tender, which has a hefty lead weight and pickup for track power. Installing the Lokpilot decoder was simple plug 'n play, and it drives perfectly so far (knock on wood). I didn't mess with any of the capacitors or coils-- it drove well after the decoder was installed, so I never opened it up again except to (eventually) add a power socket for the sound car.

Sound Conversion: This was my first sound car project. I'd scoped out the loco and tender and didn't feel that I could make it happen in the space available. Although I would have preferred to use the baggage car for the sound project (it's supposed to be the first car behind the locomotive), I only had one and they're hard to come by. I did have a spare/duplicate 1st class coach that I was willing to sacrifice to the experiment.

This was a fairly difficult conversion because the coach has so many windows and a detailed interior. The free space was a little over an inch at both ends, and I did have to carve away some cabin interior to house the dummy motor (if I'd only known about using a resistor instead...). It's not as noticeable at the ends because the private cabins were walled off from the central passenger seating. I cut enough space to house a capacitor/diode/resistor assembly next to the motor, but couldn't use a 2200 uF capacitor recommended by ESU-- not enough room. The other end housed the sound decoder and the jumble of wires that I was reluctant to snip off.

I later removed the capacitor and added a plug to share track power with the locomotive. Yep, it's ugly, but this was a necessity since the capacitor couldn't overcome the horrible reliability problems of the Arnold power pickups, which have an unconventional design:

Tiny copper springs are pressed against each axle. On the other end, the springs are pressed against a fixed copper plate which feeds track power to each end of the car. The Arnold coaches were originally fitted with a light bar holding an incandescent bulb and reflector in the center. For the standard coaches, it was easy to replace the light bars with flicker-free LED assemblies. Due to the capacitors in the LED light bars, they work reasonably reliably and mostly flicker-free as long as the train is moving and the power pickup springs are in good shape.

In the standalone sound car, the power pickup deteriorated quickly. I reasoned that the decoder and motor were drawing a lot of power through the tiny springs, which had been designed for the lower current draw of a DC lighting system. I tried to stretch some springs out for better contact, but they seemed to be stuck in the channels through the plastic trucks. They had probably heated up from the higher current and fused in melted plastic. The LED circuits didn't demand as much current, so they were okay. The easiest solution was to have the car draw power from the loco, which had contacts rated for the job. The shared power solution worked so well that I decided that I didn't need a keep-alive capacitor.

The speakers were another big challenge. I'd bought a package of 2 x 13 mm round ESU speakers since the supplied Loksound speaker wouldn't fit. The speakers alone would fit the width, but not with the baffle attached to the backside (conventional speakers). I decided to mount them on the bottom, facing downwards, mounted stuck through holes cut through the floor. A section of the cabin-long metal weight was cut out to create space behind the speakers, extending into the shallow space between the weights and the cabin floor. A little space behind the speakers was better than none, and I didn't want to cut up into the detailed cabin interior. The speakers were wired in parallel to get 4 ohms impedance, with polarity observed to make sure that they were in phase with each other (not working opposite each other to cancel out the output!).

Being tiny speakers with not much of a resonance chamber behind them, the sound was extremely trebly and sharp... but quite loud. I've since replaced them with a Sugarcube speaker facing downwards, which sounds much better-- fuller, with less treble, and very loud! It was also smaller in length and width (15 mm x 11 mm). The depth (8 mm) was greater, but still fit easily within the space, with enough clearance above the track.

I should mention that these loco/soundcar solutions require two decoders: A LokPilot for the loco, and a LokSound for the sound car. I programmed them with the same decoder address and tried to match the driving characteristics of the locomotive and the dummy motor so that the motion and chuffs were reasonably synchronized [after-the-fact note: It's much simpler to use ~220 ohm resistor instead of a dummy motor]. The challenge is getting the sound car's motor to not turn by adjusting the power curve (turning would cause unnecessary and unwanted vibration) and adjusting the driving characteristics so that the chuffs and brake sounds are fairly synchronized to the locomotive. I don't sweat over perfect synchronization throughout the entire range, or even accuracy to match the prototype. I'm satisfied with slow chuffs as the train begins to move, speeding up at the same rate as the motion in response to the throttle. The Lokprogrammer makes all this tweaking pretty easy.

As a purely practical matter, the soundcars are dedicated to a particular loco. That makes sense when decoders are built into iconic coaches like the Rheingold and Orient Express. To use them with other locos, addresses could be changed fairly quickly. However, it would be impractical to temporarily switch them to radically different locos (like electric and diesel) since soundsets can take from 10 to 30 minutes to download to the decoder.

While the Arnold Rheingold cars are very pretty, they're not an ideal candidate for a DCC sound and lighting setup. Their unique design for tapping track power may have worked adequately for DC lighting during the days when we expected lights to flicker, but there are much better designs now, more suitable for DCC sound decoders. The challenge is figuring out how to graft the new truck designs onto the pretty cars to replace the funky Arnold trucks.

 

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