July 3, 2011

The McCallum Odyssey

Tell me, O muse, of that ingenious hero who travelled far and wide after he had purchased the famous locomotive McCallum. Many cities did he visit, and many were the nations with whose manners and customs he was acquainted; moreover he suffered much by electronic gremlins while trying to bring his locomotive safely home. Tell me, too, about all these things, O daughter of Jove, from whatsoever source you may know them.
 With apologies to Homer, here begins the tale of my odyssey working on my SMR Trains Locomotive McCallum. I spent the good part of a week tuning and debugging the locomotive to get it to run reliably. Like Odysseus reuniting with his wife, in the end I was able to have McCallum running the way I want it. The breakthrough came when I swapped the McCallum's tender for Whiton's and realized the intermittent problem was in the tender.

 Lets begin  the tale with the decoder installation. Prior to installing the decoder, McCallum was not my best runner. It had problems with shorting. The front pilot truck wiper tended to catch on the turnouts. All in all it was a problem child.  Sometimes installing a decoder helps one find shorts because the sparks are very obvious compared to regular DC running. So I charged ahead, hoping I would have better luck than Patroclus at Troy.

For the McCallum, I decided to install a Soundtraxx Tsumani AT-1000 light steam decoder. The rated current is 1.0 amp. Our testing showed that the SMR locos draw about 0.70 amps at stall. Thus the current rating should be acceptable.

Soundtraxx Tsumani AT-1000 installation in boiler,
with speaker in fire box
The decoder install went rather uneventfully, thanks to my previous experience installing the decoder in Whiton. But even though the decoder worked fine and sounded good, there were problems with running quality. The loco was stalling every couple inches of running, and was shorting at several points.

Scorching on the valve gear from
shorts with the pilot truck
The shorts at the front of the engine were due to the metal wheels touching the valve gear or cylinders on my sharp curves.  I fixed the shorts on the pilot by adding a longer and stiffer spring to the pilot truck post. That raised the front of the loco enough so that the pilot wheels don't touch at cylinder or the valve gear guides. I had scorch marks on those parts so I knew exactly where the shorts were. Now the pilot truck has clearance for my sharp curves, and doesn't look odd at all.

I also spotted a short on the tender where the factory installed wiper was touching the frame near a wheel arch. But these wipers were causing even more trouble. The loco was suffering from intermittent electrical pick-up.

After much trial and error I realized the lack of electrical pick-up was coming from the tender side that is attached to the frame. I could make the loco run by touching the wheel on that side with a hot alligator clip.  I could also make the loco run by tilting the tender to that side.  The eureka moment came when I swapped the McCallum and Whiton tender. The Whiton tender runs well. When it was attached to McCallum the McCallum ran much better. This really narrowed the problem to the McCallum tender and the wheels without the wipers not getting pick-up.

The problem was actually on the other side though. The screws that hold the factory installed wipers on the tender trucks for the non-frame side (on the engineer side of the tender) were rubbing against the tender frame. This was not causing a short because I had insulated the area with nail polish. But it was causing the sprung wheels sets in the tender to lose pick up as the hard frame-on-screw contact was effectively removing the truck equalization. You could actually see the fireman side wheels raising up off the rails.

I completely disassembled the tender. Then I ground off about a 1/16th of an inch from the tender frame wheel arches with my Dremel tool and a grinding stone. Reassembling the engine universal joints is about as much fun as assembling a Microtrains 1015 coupler, but I got the drive to go together. Now the tender wheel sets and their associated gear towers can rock freely in the sprung mount without hitting the frame and the tender wheels track much better.

The locomotives Whiton and Haupt do not have these wiper screws on the tender trucks. I added pickups to those locos using a different design that does not interfere. Only McCaullum came with the factory installed wipers, and the problematic screws. I wanted to keep the factory installed wipers. So I did not remove them, but I did add a second set of wipers using the same design I used on the Whiton and Haupt.

The McCallum came with  a pick- up on only one axle of the front pilot truck.  I added a second pick up to improve electrical contact, and replaced the factory installed one since it didn't work well and tended to droop and get caught on the turnout frogs.  I used small piece of PC board and 0.020 inch brass wire to rub against the flange of each wheel. I also added some sheet lead to weight the pilot to improve it's tracking.

One additional change I plan to do is to replace the drawbar between the tender and engine with an insulated piece instead of the current metal one. The original draw bar is metal. Since the frame on the tender is opposite polarity from the frame on the engine, the draw bar can short if the insulating sleeve on the drawbar stud slips down where gravity seems to want to pull it. My solution will be to laser cut 1/8th inch thick acrylic drawbars that will help insulate.

Below is a short video summarizing the odyssey.

The failed QSI  decoder on Whiton is on its way to Tony's Train Exchange for replacement. I haven't decided which decoder I like best, QSI or Soundtraxx.

I haven't had a chance to program the Tsunami with momentum or sound options, but the QSI decoder seemed to start smoother. I do like the extra sounds it comes with the SOundtraxx like the water spout, steam blow off hiss and the short whistle blast.

Update: I did a bit more tuning on the McCallum drive. I cleaned off some excess epoxy that found its way to the back of one of the drive wheels.  That helped. I also added a couple ounces of sheet lead to the tender. There is room for more lead too. I also oiled the journals on several of my freight cars. All these fixes helped allow the McCallum to handle 8 eight cars across the layout.  It is running real nice. My only complaint is that the "electronic" noise from the motor is louder than I would like. Do you DCC gurus have any suggestions on how to reduce that?


  1. Bernie,
    one problem I found with Soundtraxx Light Steam decoders was that none of the bells sounded like a rope-pull bell. I now use the decoder that has the sound of a C-class D&RGW engine. The bell is better. Also, our experience in KC has been that the QSI decoders draw an awful lot of current and most people try to stay away from them for that reason.
    Don Ball

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