Welcome on Henk's website

find all about fiNe-scale modelling
in a scale of 1 : 160


Deploying signals using signal shafts

Using 'Wattenscheider' signal shafts is a Fremo H0 idea to deploy signals on a modular layout. Using a standard form shaft signals can be mounted on prepared modules in the planning session of a non-permanent layout during a meeting. For N this idea lead to some designs but until now it was not put into active use. Picking up from old experiments from 2012 with operation of signals over RF allowed testing such a shaft.

The signal shaft

There exists a topic about this on the Fremo Forum from the coarse scale NRE group which centers about a shaft of 20x20 mm. One idea concerns employing a piece of thick walled aluminium tube, the second one a 3D printable design. I chose the latter as it fits better to my ideas. A public version of the design can be downloaded from Thingiverse. I printed 2 items on the Anycubic Photon for rebuilding 2 short signal modules using grey resin with a few percent Monocure flex to make them less brittle.
Until now these modules employed form signals from Viessmann, but these showed to be very vulnerable, particularly failing on their electric functioning. It concerns operation with an electric coil, but this coil seems very sensitve to a minimum of applied voltage and to vibrations from transport. From the 4 modules 50% failed within a handful of operating sessions.
Since 2022 NMBS light signals can be obtained from Mafen (Spain). Availability of these signals allows testing the use of such a shaft. Theoretically this allows a change between light and form signals a by inserting the particular holder with signal into this shaft.

The signal modules in question are minimum size in length and concern a 12 mm header, 42 mm standard white pine and another 12 mm header. One of the headers is only screwed and can be taken of for access. This allows easy maintenance and mounting. The advantage of this short length is its minimal interference in a flowing scenery layout of other modules. However this length comes with a drawback as they are unwieldy to mount with (long) wingbolts due to lack of space between headers, but using press-in nuts might be the answer to that.
A small experiment with some headers and sides convinced me that longer signal modules of say 20 cm are a bad choice with respect to landscaping and will form a much larger obstruction in the coherence of a group of modules. Thus its either as short as possible or a normal module size length with shafts. When not in use the shafts are then covered with a dedicated plug fitting to the landscape.

original print
The original print of the shaft

Step 1 in preparation was cutting out the 13mm hole from the formsignal to 20x20 mm using an electric jigsaw. Clearly the cross section of the shaft doesn't fit the cross section of a standard module. This shaft was adapted by cutting off some bits using a Proxxon following the scribed black line. Redrawing the top of the shaft is #1 on the to do list.

top view
Top view with new plug for insert

The original insert has an integrated closed top, but in order to mount a signal it is much easier if this insert comes with a seperate plug with a slot. This slot allows easy mounting of the signal such that you don't have to thread each connecting wire individually through this mounting hole. In the above view the black cross shows the eccenter positon of the signal and also a ~1 mm gap that needs closing in a follow-up redesign, thus todo #2. Of course mounting the shaft further away from center of track allows a fully flat top profile, but this would also lead to an even more eccentric positioned signal, particularly for form signals this could be problematic.

Components for the insert

The Mafen signals are rather primitive, a bunch of wires with resistors connecting various leds. The resistors for the yellow and white leds were replaced to smaller values in order to radiate more light on 3.3 V use. I used the Proxxon with diamond cutter to carve a piece of double sided pcb that fitted the shaft. It connects over a double row 4 pin header for connection to an Arduino board. This allows 5 leds + common with 2 spare connections for a speed indication and V sign for junctions. Ideally the processing power also sits on this pcb, but available components won't fit that. This means first testing with seperate units until a satisfactory set-up is reached.

side view
Cross section view

Above photo shows the cross section with insert and signal fitted into the shaft and the 8 pin connector on the lower end.

helicopter view
top view

The helicopter view shows that there is room for further optimisation of the shaft and plug.

electronics and showing sign
connected to electronics

It took only adapting the existing program for the inverted led connections of the Mafen signals. This photo shows a battery operated board with 868 Mhz Radio.(Seeeduino Stalker V2.1 + XRF Wireless Things radio, perfect but both are obsolete items, thus not recommended for new designs). Same is possible with newer Arduino boards with Wifi/Bluetooth and these come with a much smaller footprint. There are various newer boards that offer same LiPo battery operation and have on board radio.

This is step one, next is a copy/paste for the second module and camouflage the wood with scenic stuff.

first order approach with ballast and grass, both modules in same state

After a lot of searching into available of the shelf electronic parts having the same functionality as these Arduino boards from 2012, I am now of the opinion the final shaft design should get different dimensions. Most electronics such as the Arduino Nano range are 18 mm wide and the next wider range is 22 mm. Also for form signals the height of a linear servo is only 6 mm with a width of 20. Thus for on-board electronics it is much better to produce a shaft of at least 25 mm width by 15 mm height. This would also make the outer edge of the shaft in line with the normal edge of the railbed. Using a wall thickness of 1.2 mm this will then give an insert with internal dimensions of about 20 mm x 10 mm this should allow to fit a whole range of cheap commercial boards priced between 6 - 12 Euro, boards with ESP32, RP 2040, Arduino Nano range etc. The power could be supplied from an external liPo 3.7 V over 2 contacts in the sides of the insert using 2 copper foil contact areas. Thus further experiments with on board electronics can be awaited for.

wide but flatter design
Exploded view of a design that is wider and more flat.

Based on the above this leads to an adapted design that is wider and flatter, with a loose plug, insert 75 mm deep, outer shaft 27.5 x 15 mm and a loose ring that fits over it to help gluing it below baseboard. Internally this is 22 mm wide and should narrowly fit the Arduino MKR and ESP boards with 22 mm width, but has some extra for the Nano range with 18 mm. For formsignals it should fit 2 Agfrc C1.5CLS 9mm linear servos available over Ali but this may require a 100mm shaft to fit the electronics too.

copyright: Henk Oversloot
date: 16 Feb 2023