Monday, 27 July 2015

Fitting Cobalt Point Motors - that was fun!

It took a lot of effort and time to get the point motors working. I completely misunderstood the way that these motors work. I got the switching working first time but getting the frog polarity sorted took a good deal of time. It all seemed very simple. I had the main power bus laid by the two stripes of copper tape laid earlier. As I had used red and black wires for the track power, I decided to use orange and blue to connect up the power to the motors.

I had made a template to help lay the points to get the  slot for the  motor fulcrum bar and for the hole to accept the wire for the frog polarity in the right places. I also made a template to fit each motor to the underside of the baseboard. Each motor was fitted using the supplied double sided pad. I did install the four mounting screws as well and they held quite well in the foam board. I was concerned that the motors may skew under whatever force was applied but, in fact, there was no pressure on the motor at all once firmly in place. The fulcrum bars were trimmed down to below rail level using a cut off disc in my Dremel. Lastly, I carefully ensured that the orange and blue wires were all installed with the same polarity.

It is very simple to configure up the motors with the correct DCC IDs. On each motor there is a small switch. Set it to the program position. Using the handset, you then send an accessory command to the chosen address. DCC Concepts recommend that you do this twice but I found that once works. Set the switch back to the run position and it is all done. I quickly set my points up using just 1 to 7 across the two boards.

I put the two baseboards together, connected the two using 9 way D Sub Connectors. It was then that I got a short across the tracks. It turned out that I had crossed the connection of one connector to its bus. How I put red to black and black to red defeats me! After sorting this out, I connected the NCE Power Cab to the bus. As I hadn't yet received my new Broadway SW7, I used my B&M RS3 as a test loco.

On connecting the NCE unit, all of the point motors carried out their self centering operation. On testing each one, they all operated as expected. I did have to adjust the slider on the fulcrum bar of a couple of the motors to ensure that the points actually closed with sufficient force to keep them in place. I then tried to run the loco and immediately got a short as it met the first frog. Two days of frustration followed. I put a posting up on RMWeb (one of the UK's big model railway forums) and got lots of ideas but nothing helped.

I built a test bed to have a clear idea what was going on but that worked correctly, so I was totally bemused. I then tried the loco through each point and found that it would go through some of them but not others. After a lot of head scratching and loss of sleep, I finally realised what was going on. When testing with a continuity tester, I found the following situation on the good points.
where the red line shows no short and the green indicates a short. This is what you expect and means that the frog is powered with the correct polarity. However, on some of the points, I found the following situation:
On these points, the frog was set to the wrong polarity. I had a bit of an epiphany when I saw that, from one perspective, all of the good points were in a facing position and all of the bad ones were trailing. Slowly, I realised that I had been thinking that the Cobalts were like the old Frog Juicers that I was using previously but they are not! The Frog Juicers start up in a random situation - so the polarity of the frog is indeterminate. This doesn't matter because, when the loco hits the point, the Juicer sorts out the polarity and puts it right if need be. The Cobalts, on the other hand, are switches that conform to the way that the logic says they should be. So, if a right hand point is set to the straight road on start up, the frog will be set the same way. This is based on the polarity of the power coming in, in the sense of which side of the bus is set to which connection. My realisation told me that a trailing point would see the polarity as opposite to a facing point and, thus, would power the frog with the opposite polarity. hence my shorts! This was quickly tested by switching the orange and blue wires on the trailing points to the opposite way to the facing and everything worked. It was pointed out, when I reported this on RMWeb, that this would also need to be done if the motor was fitted in the opposite way on a point - say because of a baseboard element being in the way. I have to say that I would have thought that this might have been indicated in the documentation but I can find no mention of the issue.

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