Serving servos (8)

Original page created on 26/12/2014.

Programming the decoder

There are two distinct steps in programming a servo decoder:

  1. Definition of the decoder address;
  2. Adjustment of the positions and the speed of the controlled turnout

Before proceeding, let’s say that you must not confuse the decoder address with those of the turnouts (or other accessories, such as mechanical signals or level crossings). In operation, you will never have to enter the decoder address. There is however a relationship between the two, which is indicated by the manufacturer. For example, for the ESU Switchpilot Servo, the decoder with address 1 controls the turnouts 1 to 4; the decoder with address 2 controls the turnouts 5 to 8, etc. This cannot be changed.

Defining the decoder address

The decoder address should be defined preferably before installing the decoder on the layout. Indeed, it’s much easier to do in “programming track” mode and, by definition, a stationary decoder isn’t moveable like a locomotive…

Some manufacturers provide a local mode of addressing even when the decoder is already in place, using local push-buttons. But it’s still less practical.

At ESU, all the decoder programming can be done with the Lokprogrammer.

Finally, a little clarification on a question that I asked myself: can I assign a certain address to an accessory decoder if it is already assigned to a locomotive? The answer is “yes”. Internally, the accessory decoder address numbers are distinct from those of the locomotives.

Setting the points positions

Of course, the method depends very much on the technical solution chosen. I can only speak about the one I have adopted. I hope, however, that my experience will be useful to you.

The servo may have a rotation range of almost 180°, depending on the brand and the type. In general, this is far too much for our application. And if we install this servo with its transmission before doing the settings, we risk causing damage (a servo is strong!)

So, let’s continue on the table, just after programming the decoder address. I recommend first defining the extreme positions of the rudder bar very close to the half-stroke, to have a movement of very small amplitude.

For example, with the Switchpilot, the CVs defining the positions (called A and B) are adjustable between 0 and 63, these values ​​giving the maximum movement amplitude. I give them values ​​near the average, say 30 and 33, which will give a probably too little movement, but without a risk for the mechanics.

Then, when the servos are installed at their final location, adjust the position of the point blades so that they are pressed (not too strong) on the counter-point rail. This will preferably be done with the decoder local setting mode using push-buttons. Finally, the speed will be adjusted in the same way, taking inspiration from this video.

In my case, I’ll also have to check whether the frog is correctly switched.

The travel time, measured on the video file, is about 1.2 to 1.3 seconds. This time may be chosen, or, if the speed is preferred, and given that the distance between the point blade and the counter-point is approximately 1.6 times greater at the 1/87 scale, you can set a duration of 2 s.

Turnout movements

In conclusion

(Almost) no more breakdown, a very low operating noise, realistic movements, the whole for a moderate cost and in a moderate size. What more do we want?