Peter's Model Railroading | The Equipment | Diesel Locomotives | PRR RS-1
S-CAB

If you have read my other engine articles, you will have noticed that I am converting all of them to using the S-CAB DCC with battery-power system. It is now this engine's turn. This was the most difficult one by far. I saved it for last, so that I'd have the other engines' conversion under my belt. You can read all about the S-CAB system in the article I wrote about it. This is what I had left for myself from the previous work I had done, which includes a Soundtraxx Tsunami DCC decoder with speaker. It was quite a mess. However, the first step I do when I start converting an engine to S-CAB is to completely strip it of all electronics. Start with a clean slate. Yes, even the speaker has to go. I don't think there is enough space for a sound-enabled S-CAB with battery-power system in this engine (but your mileage may vary).

My biggest concern was the battery. I custom-ordered the 900mAh battery, which stores 100mAh less than the standard battery that NWSL provides, but it is skinnier (25.5mm, as opposed to 30mm). However, as you can see in the photo, it is still too wide. The RS-1's body is quite skinny.

So, the solution will be to install this battery at an angle, as you can see below. However, now my concern was about the clearance between it and the truck tower (it turned out to leave about 1/8" of clearance, Pfew!).

This conversion project took me about one month in calendar time. The reason being that the conversion is not trivial, and there were about 5 sessions where I went one step forward and I had to take two or three steps back. Each time learning, of course, but it was frustrating at times. I did take my time, and when it became too much, I'd walk away from it for a day or so. After one false start, I decided to start over again. I had tried putting all of the components (the battery, the battery power supply board, and the decoder/receiver board) all in the upper part of the body. This worked, until I realized that I had forgotten to account for the OFF switch! Oops. One day I had a realization that there is quite a bit of empty space under the frame. After some trial fits, I decided that the decoder/receiver board should go there. The radio receiver would also not be fully enclosed in the metal body (I don't know if that would have had any impact, though). I decided to drill two holes in the underframe to allow the wires connecting the decoder/receiver board to go through into the body, undetected.

This is the bottom view of the modified frame.

To give myself a fresh start, I decided to repaint the entire underframe. I had missed some spots above the fuel tank before and it always kind of annoyed me (although you couldn't see it, unless you knew what to look for). I cut two scale 12" styrene square tubes, and used five-minute epoxy to glue them to the frame. Then it was off to the paint room. I also sprayed Testors Dullcote all of over the frame.

This photo shows a trial fit to see if it really was going to work. I put the frame in a bench vise to hold it up while I was working with it.

Here's a top view. I'll be routing the wires connecting the BPS and the motor control wires to one side, and the wires for the lights through the other.

The motor of this frame is held in place with two screws that are going to be covered up by the decoder/receiver board, so the motor had to be installed first. This engine makes a lot of noise when it runs. I decided that since I had the whole thing apart, that I'd try to isolate the motor's vibration from the frame, if possible. I cut some thin double-sided foam and placed it on the frame.

I then attached the motor to the frame on top of the foam. Ignore the yellow wires in this photo, because they were from a previous attempt at installing the system. As you can see, I put the styrene square tubes such that they cleared the motor body and the flywheel. The reason for the square tubes is to keep the wires coming through the floor from catching the moving parts.

I could then start installing the decoder/receiver board under the frame.

This then allowed me to hard-wire the decoder wires (orange and gray) directly to the motor. I used superglue to keep the wires attached to the motor body, so that they wouldn't get in the way. The thing to remember here is that the motor's body just clears the inside of the engine body's side walls, so you can only route things under or over the motor body.

I found this heavy-duty double-sided foam tape at Lowe's. It is thin and very strong. I cut a strip of that and glued it to the bottom of the frame. I could then press the decoder/receiver board to the tape. I made sure the receiver's antenna (the blue rectangular part) was exposed to the bottom (to help reception).

Here's a side view. Not all of the board connects with the tape, but enough of it does.

After a substantial amount of time trying to think of a creative solution to incorporate the OFF button (to turn off the battery power), I decided to use the switch that comes with the BPS board. I decided to allow access to it via the exhaust stack. The exhaust stack of the Railmaster Hobbies kit is a solid casting. I spent several evenings trying to carefully drill it out. Eventually, of course, the part broke off from the roof of the body (I had used five-minute epoxy to attach it). I broke off a drill bit in the part, which made the process even more difficult. I decided to deal with that part after the conversion project was done. So, with the exhaust stack removed, I drilled a hole in the body, and placed the switch under it, exposing the push button. There isn't much glue surface on the switch itself, so I built a larger wrapper around it with styrene, to provide me with more glue surface. I then used five-minute epoxy to attach the switch to the inside of the body roof. The other side of the wires to the switch have a miniature two-prong plug.

The next project is to install the battery power supply (BPS) board. The issue is making sure that the many wires stay away from the moving parts inside the engine. I decided to mount the BPS board to a piece of styrene that will sit over the rear truck tower. The double-sided tape works great on styrene too.

I could then attach the BPS board to the styrene "shelf". I placed it such that the two large inductors connect with the tape. The issue here is that the BPS board has the ON switch (a reed switch). This needs to be within about 1/2" of the magnet on the pencil. I first tested to make sure the magnet worked through the diecast material of the body shell, and it does. It turns out that the diecast metal is not magnetic, and it passes the magnetic energy on through to the reed switch. I used the caliper to determine just how high the board-on-the-shelf was to sit. The caliper is set to the inside depth of the body.

I then cut and glued two pieces of styrene (all 0.040" thick), one for each side, and glued it to the shelf. When dry, I was able to glue the whole assembly, using five-minute epoxy, to the frame itself (about half an inch of the left side of the assembly is attached; the rest floats). Note that the truck tower needs clearance to swing.

Note that the two gray wires coming off of the BPS board are hard-wired to the rear truck. This is the track power pick-up. I decided to not run a wire from the front truck, to reduce the clutter of two extra wires running through the body. If this becomes an issue, I can add those later. You may have noticed that I had cut two notches into the styrene shelf earlier. I used those to route the two gray wires, to keep them clear of the spinning drive shaft. Yet, those wires need some play, because they are directly attached to the side of the truck tower which swivels.

I then hooked up the battery, put the frame on a stand, and I was able to test the basic motor operation. It worked right away, except, of course, the motor leads were hooked up backwards. I decided that I'd fix that by flipping CV29 of the decoder.

It is now time to install the battery. I used three pieces of the double-side foam to install it into the body. That way I can remove it should the battery need replacing in the future.

I had to rework the wires for the lighting, especially the rear light, because too many things were bunching up and not allowing me to fit the frame to the body. I routed the white and blue wires (the blue one was split into two wires) down the side of one square tube, connected the current-limiting resistor, and used superglue to hold them to the frame. At the rear of the engine, I soldered a miniature connector, which mates with the one I soldered to the rear light LED. The wires for the front LED also have a miniature connector. Note that I had already installed the miniature connectors for the battery and the OFF switch wires. This allows me to completely remove the body from the frame, should I need to.

Here's a close-up of the rear light wires routed along the motor and the styrene shelf (they clear the inside of the metal body).

I have included a couple of overall photos, if you are interested in following this installation. The loose wires you see are all routed into the triangular cavity by the battery when I install the frame to the body.

A view from the other overhead angle. I did have to remove the interior (crew, equipment, etc.), because they interfered with the BPS board. Since the engine cab is wider than the body, I might be able to re-install the crew on a modified shelf and still clear the BPS board.

And a top-down view (sorry about the photo being out of focus). The only wire that needs some adjusting is the one for the rear light. I had made it purposely short, because it would get entangled in the truck and drive shaft before. There is some space in between the truck and frame to use a small pair of tweezers to move the wire out of the way of the truck tower once the frame is put in position.

If you have read my other installs you will have already noticed that I have been going back into each of my engines and installing a second reed switch. This one replaces the on/off switch that comes with the BPS board (the one connected to the orange wires). I installed the second reed switch near the front, brakeman side of the engine. I built up a bit of styrene structure to which the reed switch was attached. I soldered the orange wires to the switch. As you can see in the photo, the one under the short hood (mounted to the BPS board) is the one I use to turn the battery power on (if there is no power on the track), and the one near the front of the engine is used to turn the battery power off. It works great! I removed the physical push-button switch from the engine's roof.