Saturday, 13 June 2020

The Garden Railway: Fabian the Krokodil

You know how it is with eBay when you bid on something. You have the winning bid for days, then in the last ten minutes a bunch of robo-bidders go to work and the item sells for twice what you thought you'd get it for. So I was very pleasantly surprised to get a message telling me that my bid for our latest LGB locomotive had succeeded. I'd been thinking about getting a new train for the garden railway for a little while. I was very tempted by LGB's DR Class 99 2-10-2 steam engine, a huge monster of a thing which I once saw in real life on the Hartzquerbahn in the former DDR. But the new production is selling for nearly $2000, and isn't available yet anyway. That seems like a lot for a toy train.

So when I spotted a Rhätische Bahn Krokodil at a very good price, I just couldn't resist. My winning bid was less than a quarter the price of the steam engine. And a few days later he showed up, and the fun started.

The original Rhätische Bahn Krokodil, class Ge 6/6, in a suitably Swiss setting
The real-life Krokodils appeared in 1921. The Rhätische Bahn, which operates (still) an extensive metre-gauge network in the Swiss Alps, was a pioneer of system-wide electrification. Starting in 1919, and completed by the mid-1920s, the overhead line covered the whole network providing electricity at 11,000 volts and 16⅔ hertz.

They acquired some extra-powerful locomotives, officially called Class Ge 6/6, to pull the heaviest trains. The design, with a snout at each end holding a giant electric motor, was needed because of the sharp curves on the line. Similar, but larger engines had already been built for the Swiss main line. They had even longer, flatter snouts, and the name Krokodil (meaning, of course, Crocodile) was an obvious choice, applied subsequently to all similar engines. The driver sat in one of the cabs at either end of the central section, enjoying excellent protection in the event of a crash yet also excellent visibility. The centre section held a huge, heavy transformer, to convert the high voltage scraped off the wires by the pantographs into something like 600 volts for the motors.

All of our engines have names - Marcel the diminutive French 0-6-0 who was the subject of my intelligent locomotive experiments, Helmut the beefy Hanomag 0-6-6-0 Mallet, and so on. A few years back we visited Cancun, in Mexico. We had dinner one evening on the terrace of a restaurant overlooking the lagoon. When the kitchen was closing the cook came out and threw a whole chicken into the lagoon, as he softly called "Fabian, Fabian". There was a splash and a scurry in the water. The chicken was gone. Fabian was their semi-tame crocodile who lived in the lagoon and showed up for dinner every evening. Later we could see him gently rocking to the dance music that was playing downstairs. And so Fabian was the obvious name for our Crocodile.

The big challenge with these old LGB locomotives is converting them to run with the DCC control system on my railway. This puts a permanent 18V AC on the rails, superimposed with a control signal that tells each engine what to do. The advantage is that you can have as many trains as you want, some moving and some standing still, without any complicated wiring. A little decoder in each engine understands the control signal and turns the 18V AC into something suitable to drive a DC motor. It's hard to imagine operating a serious-sized railway without it, nowadays. Modern locomotives are designed to connect easily to a decoder, with the electrical pickups from the track wired separately from the motors.

But the old LGB ones, like Fabian, date from the time when the rails were connected directly to the motor, which was operated by a variable DC voltage on the track. The connection is typically buried deep inside the workings, and so it is with Fabian. I approached the open-gearbox surgery with trepidation, after reading web articles about the number of tiny parts that were just waiting for a chance to leap across the room and get lost in the carpet. In the event it wasn't too difficult. The internal connections are made by complex shaped brass strips that rub against all the right places, and it just took a couple of cuts to separate them. It was also necessary to run an extra wire from each bogie into the main body, so there could be three completely separate circuits: track power, motor, and lighting.

Like all older LGB locos, Fabian has a fearsomely retro-looking circuit board full of randomly placed through-hole components and massive hand-soldered tracks, that operates the lights from the track power. Rather than attempting to reproduce what it does, I prefer just to give it a fake track power feed and leave all the existing light circuits untouched. A little bridge rectifier produces 18V DC, which is then fed via a reversing relay to the circuit board. I have a stock of bistable relays, that remember their last setting mechanically, left over from another project (30 years ago!). All it takes is a couple of diodes feeding the actual motor supply from the decoder into the two relay coils, so the lights reflect the last way the train ran.

At least, that's the theory, and the way it works on my other engines. But for some reason the relay didn't want to cooperate. I think it must be defective, but anyway I ended up building something a lot more complicated, packed into board space that wasn't really available. It was a nightmare to get it to work, and I still don't understand why.

Finally everything worked. Reassembling Fabian's body was an interesting challenge. The mechanical design is ingenious, as always with LGB. To remove the circuit board required removing the back of the driver's cab. That is held in place by the hinge of the opening driver's door. Reassembling that, with the tiny spring that holds it shut, requires about six hands. With only two hands, it can eventually be done with patience and lots of not-in-front-of-the-children language.

Fabian, with his mentor Helmut looking on
Fabian looking very purposeful
Finally Fabian was ready. While he was on the bench, his train had shown up. LGB has a strange policy of constantly changing what is available new. They have made RhB wagons on and off, over the years, so finding a complete train requires a search of eBay, new production, and dealers' old stock. For now I have managed to accumulate three, with another on its way from England. Helmut generously agreed to lend Fabian his bright yellow banana wagon, but with a condition - he also had to take the track cleaner, a rather nondescript affair loaded with logs to held it scrape the oxide layer off the rails. It's surprisingly effective, but hard to pull and inclined to fall off the track. I'm sure Helmut believes he got the better part of the deal.

So now I can watch Fabian touring our garden at his stately speed - in real life he is limited to 55 km/h, even when pulling the optimistically named Glacier Express. Thanks to the wonders of JMRI and the Raspberry Pi Zero W, I can sit and sip my pastis and control him from my iPhone - but that is another story.

Fabian with his Rhätische Bahn train along with the borrowed banana wagon and track cleaner



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