Switch between multiple command stations


Reasons for the command station switch

FREMO layouts with significantly more then 300m of modules are set-up at the larger meetings. With this size multiple command stations are needed, requiring a switch to let trains move from on command station to another. At Alsfeld with close to 1000m of modules six command stations were used.

DCC Data Rate

The main reason for this is the DCC data rate. With an increasing number of trains the command station cant send all information fast enough to the trains, without a noticeable delay between command at the throttle an the reaction of the engine. This not only makes switching more difficult, but also results in the operators to turn the knob more often to get a feeling for the delay. This happens unintentionally and automatically and results in even more data to be transmitted. From about 25 to 30 moving engines the delay becomes significant.

With automatic operation this problem will appear much later, as a computer will not change the speed that often as a manual operator. This results in less data to be transmitted. But with 120 engines the limit is reached in any case, as a LocoNet command station can't administer more active addresses. It is hard to tell, whether this limit was reached in Alsfeld. Who can tell how many of the 440 trains per session and the large number of switchers have been active at the same time. It is better, not having to case about this.

LocoNet Cable Length

Another reason is the maximum Cable length of the LocoNet. The wiring along all branches of the layout, connecting all LocoNet boxes, partially mounted on both sides of the modules, and to all boosters results in more cable length then module length. Additionally the split into several RailSync districts requires extra cables, as the separate feeders needed are often more then 25m per RailSync district. Also the coiled cables of the throttles results in extra load.

The resulting cable capacitance shortens the length of the high level Bits. With the 15 mA current source there is a simple tool. But this has its limits. At Alsfeld theses current sources were needed for at two command stations despite the sectioning of the layout.

Reasons for the LocoNet Gateway

If the track is switched automatically between the command stations, there is the problem of the engineer loosing control over his train and would therefore need to plug his throttle into the LocoNet of the command station at the same time. But how should he know when the track is switched? Therefore the initial idea was to switch the throttle from one LocoNet to the other. But tests have shown new problems due to this switching and exposed old problems as well.

Re-acquiring of the Address

First more and more times the throttle entered emergency stop. This is expected, when the command stations still knows the address with a different direction, i.e. the address has not been "purged". But this could not explain to have sometimes the same problem with addresses, which had never been used on the other command station before. This happens when a new FRED with software version ≥ 1.4 logs in, reserving the slot using a Null Move (MOVE_SLOTS) as it should be done, and the direction of travel is different. This is the case, when the slot is empty = "FREE", the direction in the slot is forward per default, and the engine travels backwards.

Therefore with a new FRED this happens always, if the engine travels backwards (with Diesels cab #2 first) and is not known at the new command station. But it happens as well, if the engine is known, the slot has been become "COMMON" or "IDLE" by purging and the direction has changed.

With the first automatic switch another phenomenon turned up, where the engine reverts for a short moment. This happens when an older FRED with software version < 1.4 logs in, reserving the slot using simply a WR_SL_DATA, and the slot status is "COMMON" with a different direction of travel. The FRED takes control over the engine without entering emergency stop as the slot was not "IN USE" and therefore neither ID nor direction is checked. But as the track is switched immediately to avoid shorts and the FREDs needs time to log in, for a short time the engine gets commands with the old speed and direction.

Status of Functions

Is the throttle just plugged or switched from one command station to another, it logs in with the stored engine address. The speed is given by the setting of the pot, the direction due to the setting of the mechanical switch. But the status of the functions is lost. Command station and throttle assume all functions to be off. Bus as the functions are send not or seldom, the status in the engine and the controlling system are different and changing function state results in unexpected behaviour.

Without the LocoNet Gateway throttles without a pot for the speed and a mechanical switch for the direction could not be used on layouts with multiple command stations.

Both types of problems are solved by the LocoNet Gateway. When a throttle is plugged into the inner net provided by the LocoNet Gateway, the Gateways takes the data from the command station, where the address has been used last, transfers this status to the other command stations.

Double Track Lines

If the LocoNet is switched together with the track, not only one track power switch is needed for each track but you get two LocoNets as well, as the two tracks are never switched at the same time. Therefore the engineers need to plug into the right LocoNet. The test in Cloppenburg showed that even with explaining this before each session and labelling of the LocoNet boxes errors are made. This results in engineers loosing control over their train.

With the LocoNet Gateway al this is not needed. It doesn't matter from which command station the train receives its commands and therefore on which track it is running. Therefore one LocoNet Gateway is sufficient and also one inner net even with double track lines.


The manual Solution

At the Millenniums meeting 2000 in Kassel we had for the first time two command stations on a single layout. For this set-up I built a switch as described in the article "Zwei Chiefs in Kassel" in Hp1 2/2000 (sorry, only in German). Chiefs as command stations as the other LocoNet based command station, the Intellibox from Uhlenbrock, does not take the speed step setting from the FRED and therefore the speed steps of each engine would have to be set at all command stations.

With the years this switch was regularly used. It was copied to allow the split between the command stations to be at double track lines. But the usage has shown that the train crews have to co-operate. With many people at the big meetings it is difficult to explain this technique sufficiently. Also the operation of the switch is forgotten due to the operating stress, resulting in shorts. The operation of the switches may be the duty of the station masters of the neighbouring towns, but with a lot of traffic this isn't safe as well. And a position only operating the switch is not very attractive and hard to men, if we are short of personnel. Situations like 2004 in Cloppenburg, where the switch can be combined with an absolute block section, are rare. The picture shows the four buttons for the switch.

Buttons of the manual switch (43K)
Figure 1: Buttons for the manual switch on a double track line.

The Automatic Solution

Base on this a new solution was needed for the anniversary meeting 2006 in Alsfeld was needed. Especially many groups participated in the big layout, which usually do not visit larger meetings and therefore have little experience with the use of multiple command stations. Also we needed more than two command stations, resulting in several places with transitions between command stations. The switches therefore needed to be automatic without assistance of the train crews or station masters.

Testing the automatic switches (70K)
Figure 2: Testing and debugging in Cloppenburg.
Photo: Tobias Meyer

Therefore in preparation for Alsfeld I build eight switches and tested them thoroughly 2006 at Cloppenburg. While the switching of the track power worked very well, the switching of the throttles resulted in the problems explained above. The analysis of these problems showed the need for LocoNet Gateways, which provides a special net – the inner net – for the throttles in the switched section and connects the command stations in a useful way.

Within just three month this LocoNet Gateway was developed and tested at the meeting in Hotteln. At Alsfeld six of these Gateways were used. The switches tested in Cloppenburg were used as track power switches only. Seven of these units were used. The different count results from the two track power switches at Delthin, covered by a single LocoNet Gateway.

Foto (55K)
Figure 3: Track power switches and LocoNet Gateway in Alsfeld between Spaxingen and Rehbrück.
Photo: Olaf Funke

After the anniversary meeting the systems were distributed and will be stored at different places to be used by different groups. Therefore the switches with all their accessories are packed into boxes and a packing list is provided, to avoid loosing parts or to replace parts if needed.

Valid HTML 4.0!